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- Front Matter: Volume 7854
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Front Matter: Volume 7854
Front Matter: Volume 7854
Show abstract
This PDF file contains the front matter associated with SPIE
Proceedings Volume 7854, including the Title Page, Copyright
information, Table of Contents, and the
Conference Committee listing.
Session 1
Physics-based processing for terahertz reflection spectroscopy and imaging
Show abstract
The spectra obtained from Terahertz (THz) reflection imaging can be distorted by scattering from rough interfaces,
layers, and granular inclusions. Since the facets of the object being imaged are not generally aligned
normal to the THz beam, the received signal is produced from diffuse scattering, which can be appreciably lower
in signal strength than specular returns. These challenges can be addressed with advanced signal processing approaches
based upon the coherent and incoherent combination of returns from multiple sensors and frequencies.
This paper presents two examples of physics-based processing strategies applied to THz imaging spectroscopy.
The first method is based on synthetic aperture processing of a 2D sensor array to provide variable depth focused
images of buried inclusions (a ball bearing embedded in polyethylene sample). The second method uses correlation
processing to coherently combine multiple sensors and multiple frequencies to extract material signatures
from measurements of THz scattering from rough interfaces. Results for both methods show an increase in
performance relative to conventional imaging or spectroscopy approaches.
The study of THz wave propagation feature in atmosphere
Show abstract
Terahertz(THz) transmission can be divided into passive transmission and active transmission, passive transmission
refers to atmospheric propagation, active transmission means not only transmission but also completing a function, so
also can be said functional transmission.Knowledge of the transmission of terahertz wave is very important for terahertz
technology and its applications. We analysis detailed the atmospheric propagation model of terahertz wave, propagation
effects, propagation equation, then carry out atmospheric propagation measurement system based on THz-TDS.
THz-infra-UV transmission spectra of BGO:Ca/Pb crystals
Bihui Hou,
Na Li,
Wei Hao,
et al.
Show abstract
The THz-Infra-UV transmission spectra of Bi4Ge3O12 (BGO) and BGO:Ca, BGO:Pb crystals have been measured
at the room temperature. The forbidden gap Eg of electronic energy bands are about 3.66eV (339nm). The quantities of
adulteration Ca2+ and Pb2+ were very little (0.02 wt %), it did not influence Eg and the breadth of phonon absorption.
The high frequency edge of the phonon absorption of the crystals was at 1700cm-1 (or 51THz). The low frequency
edge of the phonon absorption was at 66 cm-1 (or 1.98THz). Below 2.00THz the transmission T(1/λ) largened, maybe
a nice transmission would be below 2.00THz in the three samples. The influence to the transmission from impurity
Ca2+ ion was smaller than 10%, and from impurity Pb2+ion was smaller than 5%. Below 2.00THz the transmission
T(1/λ) largened in the three samples.
Science, technology, and application of THz air photonics
Show abstract
The significant scientific and technological potential of terahertz (THz) wave sensing and imaging has been attracted
considerable attention within many fields of research. However, the development of remote, broadband THz wave
sensing technology is lagging behind the compelling needs that exist in the areas of astronomy, global environmental
monitoring, and homeland security. This is due to the challenge posed by high absorption of ambient moisture in the
THz range. Although various time-domain THz detection techniques have recently been demonstrated, the requirement
for an on-site bias or forward collection of the optical signal inevitably prohibits their applications for remote sensing.
The objective of this paper is to report updated THz air-plasma technology to meet this great challenge of remote
sensing. A focused optical pulse (mJ pulse energy and femtosecond pulse duration) in gas creates a plasma, which can
serve to generate intense, broadband, and directional THz waves in the far field.
Session 2
2D THz and GHz signature for identification of explosive on reflected THz signal
Show abstract
The method of THz spectrum dynamics analysis (SDA - Spectral dynamics analysis - method) is applied for the
detection and identification of substances by using the signal reflected from sample. It allows to obtain the spectrogram -
composite Fourier spectrum dynamics - of the signal and to analyze the dynamics of many spectral lines simultaneously,
even if the measurements are made on short time interval (less than 50 ps). The efficiency of the SDA method used for
longer time intervals (more than 100 ps) is discussed also. The Fourier-Gabor sliding window method is used for
obtaining the spectrogram.
We consider the examples of finding the pure RDX and harmless materials (L-Tartaric Acid, Sucrose, PTFE) or their
mixture in pellets by using a THz pulse reflected from them. A THz pulse with a few cycles falls on the sample and
reflects from it. The receiver makes the discrete measurements of electric field strength of signal reflected from the
sample. To restore the signal to the required accuracy the SVD - Single Value Decomposition - technique is used.
Our investigations show that the spectrograms and dynamics of several spectral lines of the THz pulse reflected differ
from the corresponding spectrograms and dynamics of spectral lines for the reference pulse under certain conditions and
hence it is possible to detect the presence of the material in the sample of interest. The comparison of the Fourier
spectrum of the substance with the corresponding spectrum calculated on the base of using an autocorrelation function
for obtaining the spectrum shows that the AC-spectrum gives us essential less information about substance.
From our consideration follows that in some cases the analysis of reflected signal on the short time interval (less than 50
ps) is insufficient for the reliable identification. It is necessary to analyze the response on the long time interval (about
300 - 400 ps). The analysis of spectrogram and spectral lines dynamics on the long time intervals gives the additional
information about registering sub-pulses, which are appeared due to multi-reflection of THz wave from the boundaries of
sample and from the reflecting elements of set-up, and relaxation times of excited energy levels of molecules. Hence, the
reliability of identification increases.
Terahertz spectroscopy properties of the selected engine oils
Show abstract
Engine oil, most of which is extracted from petroleum, consist of complex mixtures of hydrocarbons of molecular
weights in the range of 250-1000. Variable amounts of different additives are put into them to inhibit oxidation,
improve the viscosity index, decrease the fluidity point and avoid foaming or settling of solid particles among others.
Terahertz (THz) spectroscopy contains rich physical, chemical, and structural information of the materials. Most
low-frequency vibrational and rotational spectra of many petrochemicals lie in this frequency range. In recent years,
much attention has been paid to the THz spectroscopic studies of petroleum products. In this paper, the optical properties
and spectroscopy of selected kinds of engine oil consisting of shell HELIX 10W-40, Mobilube GX 80W-90, GEELY
ENGINE OIL SG 10W-30, SMA engine oil SG 5W-30, SMA engine oil SG 10W-30, SMA engine oil SG 75W-90 have
been studied by the terahertz time-domain spectroscopy (THz-TDS) in the spectral range of 0.6-2.5 THz. Engine oil with
different viscosities in the terahertz spectrum has certain regularity. In the THz-TDS, with the increase of viscosity, time
delay is greater and with the increase of viscosity, refractive indexes also grow and their rank is extremely regular. The
specific kinds of engine oil can be identified according to their different spectral features in the THz range. The
THz-TDS technology has potentially significant impact on the engine oil analysis.
Direct detection behavior of a superconducting hot electron bolometer measured by Fourier transform spectrometer
Show abstract
In this paper, the direct detection behaviors of a superconducting hot electron bolometer integrated with a log spiral
antenna are investigated by using Fourier Transform Spectrometer (FTS). We find the response of the bolometer to a
modulated signal can be detected by a lock-in amplifier not only from the DC bias current, but also from the output noise
power at the IF port of the HEB. We attribute the response in output noise power to Johnson noise and thermal
fluctuation noise. Both the current response and the output noise power response measured at different bias voltages can
be explained by one dimensional distributed hot spot model. In addition, the frequency response of the hot electron
bolometer measured from the response in DC bias current is in good agreement with that in IF output noise power.
Terahertz spectrum of Acesulfame-K
Show abstract
Terahertz time-domain spectroscopy (THz-TDS) is a new coherent spectral technique. The spectral
characteristics of Acesulfame-K in the range of 0.2-2.6THz had been measured with THz-TDS. We
obtained its transmission spectrum, refractive index spectrum and absorption spectrum at room
temperature in the nitrogen atmosphere. The results show that Acesulfame-K had the abnormal
dispersions at 0.40THz, 0.66THz, 0.94THz, 1.79THz and 2.30THz. The vibration absorption
spectrum of single molecule of Acesulfame-K is simulated based on the Density Functional Theory
(DFT). It is found that Acesulfame-K has the obvious absorbance in THz region. This result shows
that THz-TDS has a potential application in the field of food security.
Session 3
Terahertz photon production from cold atoms inside an optical cavity
Show abstract
The Dicke model was proposed by Dicke in 1954 to describe a single mode of photon coupled to an
assembly of N atoms with the same strength. It was found that there is a quantum phase transition from
a normal phase at weak coupling to a super-radiant phase at strong coupling at the thermodynamic limit
N =∞. Here, we solve the model at N ≥ 1 and also discuss its possible experimental implementations
inside a cavity. By studying the Dicke model by 1/N expansion, we identify an emergent quantum
phase diffusion mode inside the super-radiant phase and also work out many remarkable experimental
consequences of this mode such as its low frequency, photon number squeezing properties and photon
statistics. The energy of the phase diffusion modecan be continuously tuned into many frequency
ranges from Micro-wave to Terahertz (THz) to Infra-red. The photons from the super-radiant phase are
in a number squeezed state with much enhanced signal/noise ratio which may have wide applications in
quantum information processing. The photon statistics is strong sub-Poissonian. The effects of
dissipations due to leaking photons out of the cavity are also discussed. The connections with the recent
experiments of the strong coupling of a BEC of N ~ 105 87Rb atoms to the photons inside an
ultrahigh-finess optical cavity are carefully analyzed. Several experimental schemes to detect the phase
diffusion mode are proposed.
An efficient optically pumped terahertz laser without metal-mesh mirrors
Show abstract
The efficiency of a simply designed optically pumped terahertz laser is studied experimentally. The terahertz laser cavity
only consists of a quartz glass tube, an antireflection-coated Ge window and a SiO2 window. The Ge crystal acts as the
high-reflectivity mirror of terahertz radiation and the input coupler of pump laser instead of complicated metal-mesh
mirrors. The Ge crystal is near 3 mm thick, whose exact thickness is designed according to etalon effects to maximize
terahertz reflectivity. NH3 gas is filled in the cavity as the active medium and pumped by a TEA CO2 laser. As high as
25.9 mJ terahertz radiation at the wavelength of 151.5 μm is extracted from 1.76 J pump energy. The corresponding
photon conversion efficiency of this terahertz laser reaches 41.5%. A 4.7-mm-thick GaAs crystal and a 6-mm-thick ZnSe
crystal are also chosen to be the input coupler. The experimental results show that the efficiency of the Ge window is
54% and 66% higher than that of the GaAs and ZnSe windows, respectively. The reason of the higher efficiency of the
Ge window is demonstrated experimentally and theoretically in this paper.
Session 4
An analytical investigation of excitonic absorption in terahertz-driven quantum wells
Show abstract
An analytical solution of the optical susceptibility of quantum wells driven by a terahertz (THz) field is achieved
based on the density-matrix formalism. A simplified three-level model is adopted for the quantum well structures,
with the levels coupled by a near-infrared (NIR) and a THz field. The equation of motion for the polarization is
derived from Liouville's equation for the density matrix. Using Floquet's theorem, and under the rotating-wave
approximation with respect to the NIR probe field, analytical expression for the optical susceptibility of the
driven quantum wells is obtained. Different features rising induced by the driving THz field in the absorption
spectrum of the NIR probe are discussed for the THz field near resonance and out of resonance of the intraexcitonic
transition. This analytical investigation of the susceptibility of the THz-field-driven quantum wells is
much useful for clearly identifying the physical principles obscured in the full numerical calculations.
Superconducting integrated THz receivers: development and applications
Valery P. Koshelets,
Andrey B. Ermakov,
Lyudmila V. Filippenko,
et al.
Show abstract
A Superconducting Integrated Receiver (SIR) comprises on one chip all elements needed for heterodyne detection: a
low-noise SIS mixer with quasioptical antenna, a Flux-Flow Oscillator (FFO) acting as a Local Oscillator (LO) and a
second SIS harmonic mixer (HM) for the FFO phase locking. Light weight and low power consumption combined with
nearly quantum limited sensitivity and a wide tuning range of the FFO make SIR a perfect candidate for many practical
applications. In particular, the SIR developed for novel balloon borne instrument TELIS (TErahertz and submillimeter
LImb Sounder) covers frequency range 480 - 650 GHz. As a result of recent receiver's optimization the DSB noise
temperature was measured as low as 120 K for the SIR with intermediate frequency (IF) band 4 - 8 GHz. The capability of
the SIR for high resolution atmospheric spectroscopy has been successfully proven with scientific balloon flights from Kiruna, North
Sweden. Diurnal cycles of ClO and BrO has been observed with BrO line level of only about 0.5 K. Possibility to use the
SIRs for analysis of the breathed out air at medical survey has been demonstrated.
High transmittance and wide pass-band filter based on a three-layer structure of metal-dielectric-metal hole arrays
Show abstract
In this paper, square lattices of air holes were fabricated on a three-layer structure of metal-dielectric-metal using
micromachining technology. The metal-dielectric-metal structure is based on RT/duroid 5870 produced by Rogers
corporation. The square period is 400 μm and the radius of circular hole is 100 μm. The thickness of the structure is
about 863 μm with metal thickness of 39.2 μm and dielectric layer thickness of 785 μm. The loss and dispersion of the
dielectric layer with the dielectric constant of 2.33 are low at microwave frequencies. Terahertz transmission spectra
through the sample were measured by the state-of-the-art THz-TDS system. Experimental results show that there is a
transmittance centered at 1 THz with a wide pass-band exceeding 100 GHz. Transmission spectra calculated by FDTD
method were given for comparisons and showed good agreements with the experimental results. Through analysis, the
extraordinary transmission phenomena are caused by both the Febry-Parot effect and surface plasmon polaritons existing
on the metal arrays.
Session 5
New IR detectors with small pixel pitch and high operating temperature
Show abstract
More and more systems are requested to be more compact keeping constant system performances. One of the best
approach is to reduce the pixel pitch of the IR detector while new technology improvements are carried out to
improve the detector performance.
The last developments at SOFRADIR / France for cooled IR detectors are following these trends. As a matter of
fact, HgCdTe (Mercury Cadmium Telluride / MCT) staring arrays for infrared detection do show constant
improvements regarding their compactness, by reducing the pixel pitch, and regarding performances.
Among the new detectors, the family of 15 μm pixel pitch detectors is offering a mid-TV format (384 x 288), a
TV format (640 x 512) and a HD-TV format (1280 x 1024). The latest development concerning the mid-TV
format is performed according to very challenging specifications regarding compactness and low power
consumption. Thanks to recent improvements, the MCT technology allows to operate detectors at higher
temperature (HOT detectors), in order to save power consumption at system level. In parallel, the 15μm pitch
permits to reach challenging density and spatial resolution. This Focal Plane Arrays (FPA) is proposed in different
tactical dewars, corresponding to various systems solutions.
High frequency coaxial pulse tube cryocoolers for cooling infrared focal plane arrays
Show abstract
A survey is made about the development of high frequency coaxial PTCs. The coolers cover from 30 K
to 200 K and the cooling power levels from hundreds of milliwatts to 10's W. Tests suggest that they
have the potential to provide appropriate cooling for HgCdTe-based infrared focal plane arrays from
near visible down to very long wave infrared region. The paper also discusses the efforts to realize
space qualified cryocooler technologies.
The image denoising method for MEMS based uncooled infrared imaging system
Show abstract
The uncooled infrared imaging based on MEMS has more and more broad space for development in recent years. An
uncooled thermal detector array was designed and set up using bi-material micro-cantilever structures, which can bend
with the temperature change. The effective image points of objects' infrared images which are read out by an optical
method from this thermal detector array are discrete. For this reason, the output image should be filtered based on the
gray mean value of square window, firstly. Then, each point of image can be decided to assign zero or restore the initial
gray, according to the threshold of gray value summation of the filtered image's single direction template.
Comprehensive two directions' data that is in horizontal and vertical, the final result is achieved. The experimental
results demonstrate, this algorithm can remove noise well without losing the details of objects' effective image points.
Adaptive vibration control system of mechanical cryocooler
Show abstract
Vibration disturbances generated by mechanical cryocooler, representing in a series of harmonics, are critical issue
in practical application. A control system including electronic circuit and mechanical actuator has been developed
to attenuate the vibration. The control algorithm executes as a series of adaptive narrowband notch filters to reduce
corresponding harmonics. The algorithm does not require actuator transfer function, thus ensure it more adaptive.
Using this algorithm, all the vibration harmonics of Cryocooler were attenuated by a factor of more than 36 dB, i.e.,
the residual vibration force was reduced from 3.44Nrms to 0.05Nrms over the 300 Hz control bandwidth, the
converging time is only less than 20 seconds, and the power consumption of mechanical actuator is less than half a
watt. The control system has achieved the general vibration requirement of Infrared application.
Session 6
Sub short noise 3D laser radar based on second-order coherence
Show abstract
The area array three-dimensional (3D) active imaging laser radar is a kind of remote sensing system which benefits high
detection speed. This type of laser radars employ area optical modulation devices such as micro-channels plate (MCP)
image intensifiers to modulate the photons flying time into intensity which can be detected by a charge coupled device
(CCD). The distance measurement precision of this kind of laser radars is determined by the short noise of the photons
numbers. This property limits the performance of this kind of laser radar. In this paper, a method based on second-order
coherence is presented to compensate the short noise. The analysis result shows the photon bunching effect improves the
SNR of the distance measurement with the same photon numbers. The second-order coherence based method is
proposed to prove the 3D active imaging laser radar SNR. An experiment system is introduced which has results verified
the theory.
Elimination of reflection induced artifacts in flash thermography
Show abstract
Pulsed thermography is a technique in which pulsed flash energy is applied to the surface and the
temperature of the surface is recorded and analysed. Generally the temperature above the defect areas
is different from that of the surrounding area. However, when the surface of the specimen is highly
reflective, artifact of fixed pattern could be introduced which comes from the reflection of the heated
lamp tube. Several methods were used to eliminate the artifact, including spatial filtering, image
subtraction and frequency domain filtering. Results show that spatial filtering may be the best method
of the fixed pattern artifact elimination.
Research on generated mechanism of scattering characteristic of random rough dielectric surface
Show abstract
On the basis of electromagnetic theory, the scattering light intensity from a series of dielectric surfaces
with different roughness is calculated by using monte-carlo method and the boundary condition of
Kirchhoff approximation. The geometry profile of rough surfaces obeys Guass distribution and all of
the surfaces have the same corelation length. With the increasing of rms height, the width of diffuse
scattering intensity distribution, the attenuation of scattering peak value and its moving to the normal
direction are observed. After theoretical analysis, it is obtained that the statistical distribution of the
local slope varies with the rms height and reflecting index of these local slope are the main reasons for
these phenomenon.
Session 7
Large submillimeter and millimeter detector arrays for astronomy: development of NbSi superconducting bolometers
Show abstract
The achievement of the Planck and Herschel space missions in the submillimeter and millimeter range was made
possible by a continuous effort on detector developments. Now limited by the intrinsic fluctuations of the radiation
coming from the astronomical sources themselves, the sensitivity improvement requires the development of large arrays
of detectors filling the focal plane of the telescopes. We present here the development of a TES array using NbSi sensors
on SiN membranes. The readout electronics is based on SQUIDs and a cooled SiGe ASIC multiplexer. The detector is
coupled with the input radiation by means of antenna. The present goal performance is adapted for the realisation of a
ground based millimeter camera.
New design enhancements for microbolometer PIR security sensors
Show abstract
The design and development of microbolometer passive infrared (PIR) security sensors at Electro-optic Sensor Design
(EOSD) has previously been described at the present and other SPIE forums. The primary object of this patented
technology is to provide a higher performance option to current pyroelectric PIR sensors, including longer detection
range, detection of developing fire and machinery failure, and imaging capability. A number of other applications have
been identified.
The EOSD sensor technology employs a novel mosaic-pixel focal plane detector array (MP-FPA), together with
purpose-designed optics and electronic readout to achieve high detective performance in low product cost, short range
sensor applications. In previous papers emphasis was placed on FPA design for amorphous silicon (a-Si)
microbolometers, and other materials were briefly discussed as options. In this paper new MP-FPA designs will be
described for further performance enhancement and application to vanadium oxide (VOx) and other silicon alloys,
including amorphous Si:Ge. The designs are intended for high volume production in CMOS/MEMS foundries. The
performance of different FPA designs is compared for upgrade PIR security sensors and low cost thermal imagers.
Polarization modulation terahertz filter based on metallic fractal structures
Show abstract
In this paper, the terahertz transmission properties of metallic fractal structures are presented by
the terahertz time domain spectroscopy and the numerical analysis based on the finite differential time
domain simulation. Several metallic fractal structures including the H-shape fractal pattern and the
square-hole fractal pattern are studied. The terahertz transmission spectra of these metallic fractal
structures are shown at two polarization of terahertz field perpendicularly. The results show that the
asymmetric metallic fractal structures such as H-shape fractal structure have an obvious polarization
dependent and frequency selective transmission. The symmetric structures have no such polarization
dependence. Terahertz transmission through the H-shape metallic fractal structure can be switched
between the different pass bands by changing the polarization direction of terahertz field relative to the
first-level fractal line. Therefore, a potential application may be to realize a polarization tunable
terahertz filter based on this kind of H-shape metallic fractal structure.
Session 8
TAD[sup]2[/sup]: the first truly non-intrusive lie detection system deployed in real crime cases
Show abstract
Interrogation is an important step for seeking truth from the suspect. With the limit of the intrusive nature of the current
polygraph, we show here a highly-sought-after non-intrusive lie detection system with a user-friendly interface called
TAD2. The key idea behind our TAD2 is based on the analysis of far-infrared data obtained remotely from the periorbital
and nostril areas of the suspect during the interrogation. In this way, measured change in skin temperature around two
periorbital areas is converted to a relative blood flow velocity while a respiration pattern is simultaneously determined
from the measured change in temperature around the nostril region. In addition, TAD2 is embedded with our automatic
baseline assignment that is used for distinguishing the subject's response into normal or abnormal stage. In our TAD2,
the officer can choose to perform one of the three standard lie detection tests, namely, a modified zone comparison test, a
modified general question test, and an irrelevant & relevant test. Field test results from suspects in real crime cases are
discussed.
A design study on terahertz interferometry in Antarctica
Show abstract
Terahertz interferometry from high altitude site in Antarctica is proposed. Requirements for future terahertz astronomy
are followed by comparison of interferometer technologies. Heterodyne interferometer can use matured technology and
achieve high frequency resolution, whereas, direct detector interferometer can achieve observations in large bandwidth
and wide field of view using focal plane arrays. As an example of direct detector interferometry multi-Fourier transform
interferometer (MuFT) is introduced, which utilize Martin-Puplett type Fourier transform spectrometer, which is
essential to realize multiplying interferometry to avoid atmospheric background fluctuation. As another example, photon
counting interferometry is introduced. By implementing fast response FIR detectors to measure photon arrival time,
visibility can be measured by the correlation of the photon statistics.
Time-domain terahertz transmission absorption of (Ca[sub]0.5+x[/sub] Sr[sub]0.5-x[/sub])[(Al[sub]0.5[/sub]Nb[sub]0.5[/sub])[sub]0.5[/sub]Ti[sub]0.5[/sub]]O[sub]3[/sub] complex perovskite
Show abstract
The phase assemblage and dielectric properties of (Ca0.5+x Sr0.5-x)[(Al0.5Nb0.5)0.5Ti0.5]O3O3 ceramics (abbreviated as
CSANT hereafter) in Terahertz waveband were investigated. The CSANT complex perovskite was unstable at
Ca2+-rich composition, a secondary phase were easily segregated in x ≥-0.05 region. The main perovskite phase
CSANT crystallized in Fm3m cubic symmetry in the composition range of x≤-0.1, however, it transited to Pbnm
orthorhombic space group after x=-0.1 due to the antiphase tilting of oxygen octahedra. As x further increased to
x=0.2, or the tolerance factor decreased to 0.9785, A-site Ca2+/Sr 2+ cations antiparallel displacements also appeared.
The dielectric absorption property of CSANT ceramics in THz frequency range was investigated using
time-domain transmission spectrum technology and was correlated to their microstructures. The compositional
dependence of the power absorption property of CSANT ceramics exhibited a monotonous variation in 0.1~2.5THz
frequency. A lowest THz power absorption ceramic could be obtained in CSANT compounds at x=0.3 when
sintered at 1500°C for 4hrs.
Far-infrared in vivo signature of human skin by terahertz time-domain spectroscopy using waveform rebuilding technology
Xiangjun Li,
Jianjun Liu,
Zhi Hong
Show abstract
We present terahertz time-domain spectroscopy characterization of human thumb skin in reflection measurement mode
with waveform rebuilding technology. The thumb skin contacts one side of a high resistive silicon wafer with 3 mm
thick, and here is an orthogonal incidence of the THz pulse putting on the other side of the wafer. We rebuild the time
domain signal from silicon-skin interface as a sample signal by the signal from the air-silicon interface as a reference and
a Fresnel transform function between them. Material parameters were calculated by minimizing the difference between
the measured sample waveform and a rebuilt one in time domain. The double Debye model parameters for the thumb
skin were fitted. The method has potential to research complex layer-structures in skin if a precise model is built.
Study on detection and identification model of passive teraherz imaging system for extended target
Show abstract
Detection and identification performance prediction is an important part in designing the passive
terahertz imaging system. This paper presents a novel detection and identification model of passive
terahertz imaging system for concealed extended target. In the modeling process we take into account
main factors such as radiation principle of target and background, the characteristics of atmospheric
transmission, and imaging detecting system. Firstly we research interaction principle of terahertz
radiation for object based radiation principle of low temperatures terahertz blackbody. We calculate
target and background terahertz radiation power. So target-to-background contrast is described in
different fields and ranges. Secondly, we research the effect of terahertz beam attenuation in
atmospheric environment, and choose the best terahertz atmospheric absorption frequency. So we can
account target radiation power in the surface of detector. Lastly we research passive terahertz imaging
detecting method for improving THz radiometric resolution. Due to testing target is extended, the two
dimensional real-time scanning method is adopted. So we account identification probability of passive
terahertz imaging system in different distance. The paper shows results in different distances and is
useful to design and evaluate the passive terahertz imaging system for concealed object detection and
identification.
Image fusion based on millimeter-wave for concealed weapon detection
Show abstract
This paper describes a novel multi sensors image fusion technology which is presented for concealed weapon detection
(CWD). It is known to all, because of the good transparency of the clothes at millimeter wave band, a millimeter wave
radiometer can be used to image and distinguish concealed contraband beneath clothes, for example guns, knives,
detonator and so on. As a result, we adopt the passive millimeter wave (PMMW) imaging technology for airport
security. However, in consideration of the wavelength of millimeter wave and the single channel mechanical scanning,
the millimeter wave image has law optical resolution, which can't meet the need of practical application. Therefore,
visible image (VI), which has higher resolution, is proposed for the image fusion with the millimeter wave image to
enhance the readability. Before the image fusion, a novel image pre-processing which specifics to the fusion of
millimeter wave imaging and visible image is adopted. And in the process of image fusion, multi resolution analysis
(MRA) based on Wavelet Transform (WT) is adopted. In this way, the experiment result shows that this method has
advantages in concealed weapon detection and has practical significance.
Poster Session
Analysis of bit error ratio introduced by ellipse gauss beam drift and power calculate in space optical communication
Show abstract
The bit error ratio (BER) and power are very hard to calculate in space optical communications, having lots of effect
factors, so need compromise to consider the complex factors. Analysis the influence to the BER such as beam drift, beam
divergence angle, communication distance, link loss, detector sensitivity etc. Propose the view of ellipse gauss beam can
inhibit beam drift by the random shock and relative motion of the optical platform and reduce the BER, and further
propose the method of calculate the transmit power using the BER. Experiments showed that it is security to use the
calculation methods of BER and power.
Optical properties of CuS nanoparticles at terahertz frequencies
Show abstract
The low-frequency optical properties of CuS nanoparticles in the composite samples were
measured by the terahertz time-domain spectroscopy. Then, the power absorption, refractive index,
complex dielectric function and conductivity of pure CuS nanoparticles are extracted by applying
Bruggeman effective medium theory. The measured dielectric function and conductivity are consistent with
the Lorentz theory of dielectric response as well as the Drude-smith model of conductivity in the frequency
range from 0.2 to 1.5 THz, respectively. In addition, the extrapolation of the measured data indicates that
the absorption is dominated by the lattice vibration localized at 4.7 ± 0.2 THz and the time constant for the
carrier scattering is only 64.3 fs due to increased electron interaction with interfaces and grain boundaries.
The THz time domain spectra of SrB[sub]4[/sub]O[sub]7[/sub] crystal
Yali Wang,
Bihui Hou,
Haiyan Wang,
et al.
Show abstract
SrB4O7 (SBO) is a promising nonlinear optical crystal. It has the orthorhombic structure with group classified as
Pnm2. The sample for the experiment was cut along the (001) plane and twin polishing with 1.632mm thickness. It
exhibits a wider transparency range from UV to far-IR. And its absorption edge lies at 160nm. The forbidden band gap is
about 7.76eV. The THz spectra of SBO crystal had been studied from 0.1 to 2.5THz. The THz time domain spectrum of
SBO shows the strong resonance characters. In THz experiment, the vertical incident electromagnetic waves radiate the
polished side twice along (001) orientation. The crystal turned 90 degrees relative to the first in the vertical direction.
There are different optical properties in two directions. We gained the curves of the refractive index and absorption
coefficient dependence of frequency in the region of 0.1-2.5THz. The absorption curves shows opposite parabola
character. One is upward opening and the largest absorption coefficient is 10cm-1. The other is down opening and the less
absorption coefficient is 1cm-1. The refractive index n is stable linear with frequency and it is 3 from 0.4THz to 2.5THz.
But the refractive index of two directions shows the opposite tendency from 0.1 to 0.4THz. The reason of the difference
is that polarized beam radiates the orthorhombic crystal. The properties of the sample show that it is possible to apply it
to laser field.
The optical and electrical properties of W-doping VOx thin film
He-qin Li,
Xiao-xiong He,
Lin-fei Shao
Show abstract
The thin films of W-doped VOx, were synthesized onto glass substrates using reactive DC magnetic co-sputtering
deposition technique. The optimum synthetic process was obtained when the gas pressure was 2.0Pa , the ratio of O2/Ar
was 1.0:15, the sputtering powers were 120W for vanadium target and 45W for tungsten target during 30minutes, and all
W-doped VOx films were annealed in nitrogen atmosphere at 450°C for 2 hours. The structures of films were
characterized by X-ray diffraction. The effects of W dopant on the semiconductor to metal phase transition of bare VOx
were investigated with measuring the dependence of electrical resistance on temperature and the infrared transmittance
spectra. Remarkably strong effects of W doping were observed on VOx films both the optical and electrical properties.
The IR transmittance was decreased from 67.46% to 44.86%, while the transition temperature from monoclinic
semiconductor to tetragonal metal was decreased from 68°C to 48°C through W-doped. In addition to, the temperature
coefficient of resistance was changed from -1.48 %/ °C into -1.71 %/ °C for W-doped VOx film at corresponding
transition temperature.
Propagation of THz wave in random coal aggregates
Show abstract
Propagation of a continue THz wave in random coal aggregates are studied using generalized multisphere Mie theory
and Monte Carlo(MC) simulation. Coal aggregates are obtained by the DLA model. Scattering characteristics of
monomers and aggregates in coal clouds are analyzed by generalized multisphere Mie theory. For a single coal monomer
and a coal aggregate, scattering intensities versus scattering angles are given. The effects of the radii of monomers on the
scattering efficiency factors, extinction efficiency factors and absorption efficiency factors are computed and discussed.
With the MC method, the transmission of a THz wave in a coal clouds layers is simulated.
Optical properties study on some nematic liquid crystals in the terahertz range
Show abstract
Because of its unique nature, terahertz radiation has wide application prospects in physics, chemistry,
biomedicine, communications, radar and security checks, etc. Liquid crystal, which is a kind of
macromolecule soft material with special properties in physical and chemical, has been widely used in
planar displays. Recently, much attention has been paid to non-display studies of liquid crystals,
covering the fields of biology, chemistry, physics, material and engineering. In this paper, the
transmission spectra of several nematic liquid crystals such as 5CB, TEB300, RDP-92975 are
measured by THz time-domain spectroscopy technique and free-space electro-optic sampling method.
The absorption coefficients of liquid crystals in the THz range are calculated. Furthermore, the optical
parameters are compared and analyzed, expecting to fill the spectrum gap of liquid crystals in the THz
range and provide the experimental and theoretical foundation for the application of liquid crystals.
Characterization of terahertz emission from a laser-induced air plasma with a dc biased field
Kaijun Mu,
Fei Yu,
Liangliang Zhang,
et al.
Show abstract
The generation of terahertz (THz) wave from a single-color femtosecond (fs) laser-induced air plasma with a dc biased
field is studied. A systemic investigations of the THz wave polarization by changing the direction of dc biased field in
parallel or perpendicular to pump pulse polarization. The results demonstrate that the THz wave generation is the sum of
ponderomotive force and the dc biased field, and the external dc biased field can amplify and modulate the total THz
waveform.
Polarization-controlled THz spectroscopic imaging for nondestructive inspection
LiangLiang Zhang,
Fei Yu,
Hua Zhong,
et al.
Show abstract
We present a polarization-controlled terahertz (THz) wave spectroscopic imaging modality to
investigate the anisotropy of the detected materials. The polarization of the emitted THz wave is
controlled to be horizontal and vertical by changing the relative phase of the fundamental and
second-harmonic waves in the two-color laser-induced air plasma THz generation configuration. The
anisotropy of the industrial sprayed-on-foam-insulation (SOFI) is characterized by measuring its
azimuthal angle dependent THz polarization response. This work demonstrated that THz wave
polarization-controlled imaging technique can be used for highly sensitive industrial inspection and
biological related characterization.
Reflective mode terahertz time domain spectroscopy for sealed liquid detection
Zhen-Wei Zhang,
Kai-Jun Mu,
Liang-Liang Zhang,
et al.
Show abstract
We built a reflective mode terahertz time domain spectroscopy system for
sealed liquid detection. We used air plasma THz emitter for obtaining a high THz power
of 5mW and used ZnTe electro-optic (EO) sampling for getting high sensitivity difference
detection. Experiment demonstrates this system can detect the liquid in the sealed
container. We measured the reflection data on the second interface between the sealed
container and the inside liquid. The signals from the top interface show a relation with the
refraction coefficients of the liquid in the THz region by using Fresnel's equations. The
liquid can be indentified by comparing the curves of reflection and a database of known
liquid refraction coefficients. In this paper, water, ethanol and ethylene glycol were
detected and indentified. In additional, the data processing and analysis for getting the
reflection data on the second interface are discussed.
Investigation of honeycomb structure using pulse infrared thermography method
Huijuan Li
Show abstract
To reduce weight and improve strength in the aerospace industry, composite structure has gained popularity as a
replacement for conventional materials and structures, such as adhesive bonding and honeycomb structure. Honeycomb
structures composed by a honeycomb core between two facesheets are very common on aerospace parts. However, the
adhesive bonding process is more susceptible to quality variations during manufacturing than traditional joining
methods. With the large increase in the use of composite materials and honeycomb structures, the need for high speed,
large area inspection for fracture critical, sub-surface defects in aircraft, missiles and marine composites led to broad
acceptance of infrared based NDT methods. Infrared thermography is one of several non-destructive testing techniques
which can be used for defect detection in aircraft materials. Infrared thermography can be potentially useful, as it is
quick, real time, non-contact and can examine over a relatively large area in one inspection procedure. In this paper, two
kinds of defects which are of various size, shape and location below the test surface are planted in the honeycomb
structure, they are all tested by pulsed thermography, analyze the thermal sequence and intensity graph got by this
methods, it shows that pulsed thermography is an effective nondestructive technique for inspecting disbonding defect,
can distinguish the location and the dimension of the defect exactly.
A detection technology of THz based on surface plasmon resonance
Show abstract
This paper describes a new detection technology related to the bolometric micromechanical sensor for detecting THz
radiation. The micromechanical sensor comprises thermo-sensitive bi-material micro-cantilever, micro-prism and optical
readout system based on surface plasmon resonance for detecting the bending of the micro-cantilever. In static mode,
incident radiation absorption raises the temperature of cantilever and, as a result, it bends proportionally. The cantilever
bending changes the thicknesses of the gap between the lower surface of the cantilever and the metallic thin film. It will
result in a shift of the SPR angle. Consequently, the surface plasmon excitation efficiency and therewith the measured at
a fixed incident angle reflectance of a metallic film will be changed almost proportionally to the cantilever bending.
Therefore the incident radiation power can be determined via the metallic film reflectivity change. The paper introduces
the bi-material for fabricating the micro-cantilever and the optimal thickness of the gold film which is obtained through
computer simulation. The material of silicon is used to fabricate the micro-prism, and the technique procedure for
manufacturing the micro-prism and the micro-cantilever is described in detail. Because of its uncooled performance of
the detection technology, the micromechanical sensor will have a low cost and be easy for fabrication of large
bi-dimensional arrays.
Synthesis arrangement and parity correction of linear array infrared detector
Show abstract
According to the configuration and technical specification of the detector, which has multiple channels, channels mixing,
high speed outputs and separate columns between odd and even, a real time digital processing unit based on the CPLD,
FPGA and DSP has been developed to achieve the data synthesis and arrangement function and the parity correction
algorithm. A special interface circuit with 4 CPLDs is designed to complete the first synthesis step where the 16 channels
of data are combined into 4 channels. The second step is finished in FPGA and ROM address encoder where the 4
channels of data are combined into 1 channel. For output data synchronization, FIFO is adopted to achieve the delay of
even channels in the parity correction. Data of odd channels enters the columns synthesis unit without any processing
and even channels shall be processed in the columns synthesis unit after entering the FIFO unit first and experiencing the
delay process. Thereby the pre-processing before image processing of the linear array thermal imager is accomplished.
Research of the solar photovoltaic cells output characteristics influenced by infrared wave in the solar spectrum
Bo Su,
Guoteng Duan
Show abstract
The energy of solar radiation on the earth mainly concentrates in 0.29~3μm wavelength range, where infrared wave
accounts for 53 percent, visible light accounts for 44% and ultraviolet accounts for 3%. For the photovoltaic cells,
different light coming from solar radiation has different energy and different penetration depth. For the short waves, the
photovoltaic cells have large absorption coefficient and have small absorption coefficient for the long waves. As for the
sunlight, if the photon energy is greater than the semiconductor forbidden bandwidth, it will inspire electron-hole pairs,
and vice versa. When the range of wavelength is 0.5~1.2μm, silicon photovoltaic cells can transform the light energy
into electrical energy and heat energy, and only heat energy to the light which wavelength is greater than 1.2μm. So, the
photovoltaic cells will make most of the sunlight change into heat energy, which will influence the characteristics of the
photovoltaic cells unless the heat was dissipated in time. In the paper, the thermal battery pasted on the back of the
photovoltaic cells is adopted to absorb the heat, so the photovoltaic cells can keep a good state long time. The strategy of
energy management is presented in the paper in detail.
Design of infrared images high speed transmission technology based on fiber
Show abstract
Due to the development of IR FPAs resolution and the transmission speed of the images, the requirement for the
high speed IR images transmission becomes a significant part in the whole IR imaging system. The fiber based
transmission method is proved to be a promising technique which can replace the traditional methods based on the
electrical signals. This paper introduces the design of digital IR images transmission technique based on fiber,
according to the characteristics of IR imaging data. This long wire transmission is accomplished utilizing the FPGA
which is designed to control the data cushion synthesis process, receive the high speed imaging data and send out
the real time VGA images. FPGA provides the reference clock signals to help the encoder convert the 16 bits
parallel imaging data into the serial LVDS signals. Then the MAX9376 chip is introduced to convert the LVDS
signals into the LVPECL signals, for only the LVPECL signals can be received by the laser diode. The receiving
process is just opposite, where the LVPECL signals are finally converted into the parallel data. To verify this design,
the VGA controller function is achieved by Verilog HDL programming in FPGA, so that the parallel IR imaging
data can be converted into the high resolution images. The experiment images show that the effective resolution of
the image in 64Mhz is 1024×800, and the transmission rate reaches 1.125Gb/s which is much higher than the
traditional methods and fully satisfies the requirement for the long distance IR imaging data transmission.
Holographic illumination to compensate the FPA fabrication errors for FPA IR image system
Show abstract
The FPA Infrared imaging technology is widely used in military and civilian fields, and the optical readout FPA Infrared
imaging technology is one of the most important branch. How to get a higher sensitivity IR image is very important since
there are many factories that can degrade image quality. In this paper we introduce a method to improve system image
quality, which is called the holographic compensate illumination based on the holographic technology. Firstly, we
analyze the key influencing factors of the image quality of an optical readout FPA IR imaging system, and the two kinds
of manufacturing errors of the FPA are given. Then we point out the principle of the method to compensate the FPA
fabrication errors and design the experimental scheme. The result of the experiment shows that we can get a more
uniform and higher sensitivity IR image by the method of holographic compensate illumination.
The algorithm analysis on non-uniformity correction based on LMS adaptive filtering
Dongjun Zhan,
Qun Wang,
Chensheng Wang,
et al.
Show abstract
The traditional least mean square (LMS) algorithm has the performance of good adaptivity to noise, but there
are several disadvantages in the traditional LMS algorithm, such as the defect in desired value of pending
pixels, undetermined original coefficients, which result in slow convergence speed and long convergence
period. Method to solve the desired value of pending pixel has improved based on these problems, also, the
correction gain and offset coefficients worked out by the method of two-point temperature non-uniformity
correction (NUC) as the original coefficients, which has improved the convergence speed. The simulation
with real infrared images has proved that the new LMS algorithm has the advantages of better correction
effect. Finally, the algorithm is implemented on the hardware structure of FPGA+DSP.
Experiment tests of atmospheric turbulence effects on the infrared thermal imagers performance
Show abstract
This research indicated the experiment method to analyze and predict the effect of turbulence on the performance of IR
thermal imagers. First, the values of structure constant of refractive index, Cn 2, were measured. The Cn 2 model used in
engineering applications is also introduced. And the calculated values were compared to the experiment data, so that the
model can be modified. Meanwhile, two IR thermal imagers in MWIR and LWIR bands were installed to provide the
data on the range performance. After that, the range values as a function of varying turbulence were calculated utilizing
the simulation tool. Finally, this paper analyzed the range values in different groups.
Terahertz wave opto-mechanical scanner for security application
Show abstract
This paper describes a new opto-mechanical scanner that is hopeful for terahertz imaging in security
applications. The target of using this scanner is portal screening of personnel for high-resolution
imaging of concealed threat objects. It is not only applied to active terahertz imaging but also applied to
passive Terahertz imaging. Terahertz wave can penetrate many materials that are opaque to visible and
infrared light, such as plastics, cardboard, textiles and so on. So the terahertz imaging technology has a
potential to be applicable in security inspection at airports, stations and other public place. Now, the
most terahertz imaging system works at point to point mechanical scan pattern. The speed of this raster
scan is too slow to apply in practical field. 2-D terahertz array detector can be applied to real time
imaging. But at present their cost is prohibitively high. Fortunately low cost, high performance,
opto-mechanically scanner is able to meet the current requirements. An opto-mechanical scanner
should be able to rapidly scan a 2-D image of the scene. It also should have high optical efficiency so
that an image system can achieve the required thermal sensitivity with the minimum number of
receivers. These ensure that it can easily operate at any wavelength, and be active or passive. The
opto-mechanically scanning can meets these requirements and is being developed into a high
performance, low-cost prototype system that will meet the future needs for terahertz security.
The birefringence property of magnesium fluoride crystal in THz frequency region
Fei Yu,
LiangLiang Zhang,
Hua Zhong,
et al.
Show abstract
The azimuthal angle dependent transmittance in 0.2-2.2 THz frequency region for magnesium fluoride
(MgF2) crystal is measured by using a polarization sensitive detection method. The birefringence,
absorption coefficient and refractive index have been studied. Based on the theory of crystal optics, the
possibility of using magnesium fluoride (MgF2) crystal as a THz wave plate is investigated. The
coincidence of experimental data and theoretical curve demonstrates that these optical properties are
sufficient for being used as wave plate operating in 0.2-2.2 THz frequency region.
Identification of ores and gems using THz polarization information
Show abstract
The polarization information of various ores and gems in the terahertz (THz) frequency region has been investigated.
The images of the samples for different polarization are captured by a balanced polarization imaging system. The system
employs a balanced electro-optic (EO) detection method for two-dimensional THz real-time imaging, which
systemically integrates the THz balanced EO sampling technique and the dynamic subtraction technique. The proposed
method can effectively improve the signal to noise ratio and the spectrum measurement accuracy of the imaging system.
The imaging speed is dramatically reduced by using two high speed CCDs which are used to detect two orthogonal
polarization components of probe beam. The subtraction of two corresponding images presents the balanced image of the
sample. By rotating the polarization of the probe beam by 45 degree, another polarization component which is
orthogonal to the present one can be measured. The experiment results demonstrate the advantage of the method. The
spectra of the samples on each point can be extracted from a series of images, thus the refractive indices, absorption
coefficients, and polarization rotation coefficient can be drawn. The information can be used to identify samples.
Fast calculation of object infrared spectral scattering based on CUDA
Show abstract
Computational unified device architecture (CUDA) is used for paralleling the spectral scattering calculation from
non-Lambertian object of sky and earth background irradiation. The bidirectional reflectance distribution function
(BRDF) of five parameter model is utilized in object surface element scattering calculation. The calculation process is
partitioned into many threads running in GPU kernel and each thread computes a visible surface element infrared
spectral scattering intensity in a specific incident direction, all visible surface elements' intensity are weighted and
averaged to obtain the object surface scattering intensity. The comparison of results of the CPU calculation and CUDA
parallel calculation of a cylinder shows that the CUDA parallel calculation speed improves more than two hundred times
in meeting the accuracy, with a high engineering value.
Properties study of vanadium oxide thin films annealed in N[sub]2[/sub]/H[sub]2[/sub] ambience
Show abstract
Vanadium oxide thin films fabricated by reactive magnetron sputtering were annealed in N2/H2 ambience for 1, 3, 5 and
7 hours at 450°C. Changes in electrical & structural properties and chemical composition were studied. From R-T
measurement and calculation, it was found that both square resistance(R) and temperature coefficient of resistance(TCR)
of the films increased after annealing. Atomic force microscopy(AFM) analysis revealed that both grain size and surface
roughness were aggrandized greatly after annealing. X-ray diffraction(XRD) analysis showed that new phases V2O5(0 0
1) and VO2(0 1 1) appeared in the annealed films and the grain size varied between 10~40nm. X-ray photo-electronic
spectrum(XPS) analysis demonstrated variations in depth of the atomic ratios of O:V and the vanadium valence states
distribution for different time annealed films. Following the above analysis, correlation between macroscopic and
microscopic characteristics of the films is elaborated.
The cryogenic readout system with GaAs JFETs for multi-pixel cameras
Show abstract
Our purpose is to realize a multi-pixel sub-millimeter/terahertz camera with the superconductor - insulator -
superconductor photon detectors. These detectors must be cooled below 1 K. Since these detectors have high impedance,
signal amplifiers of each pixel must be setting aside of them for precise signal readout. Therefore, it is desirable that the
readout system work well even in cryogenic temperature.
We selected the n-type GaAs JFETs as cryogenic circuit elements. From our previous studies, the n-type GaAs JFETs
have good cryogenic properties even when those power dissipations are low. We have designed several kinds of
integration circuits (ICs) and demonstrated their performance at cryogenic temperature. Contents of ICs are following;
AC coupled trans-impedance amplifiers, voltage distributors for suppressing input offset voltage of AC coupled CTIAs,
multiplexers with sample-and holds, and shift-registers for controlling multiplex timing. The power dissipation of each
circuit is 0.5 to 3 micro watts per channel.
We also have designed and manufactured 32-channel multi-chip-modules with these ICs. These modules can make 32-
channel input photo current signals into one or two serial output voltage signal(s). Size of these is 40mm x 30mm x 2mm
and estimated total power dissipation is around 400 micro watts.
Optimum design of THZ spectrum diffractive gratings
Show abstract
Rigorous coupled-wave analysis is used to calculate the diffraction efficiency of THZ spectrum gratings. The ratios of
grating periods and wavelengths and the ratios of grating depths and wavelengths of different type gratings are analyzed
in this paper. Calculated results show that if the ratios of grating periods and wavelengths approximately equal to 1 and
the grating depths greater than1.5, high diffractive efficiency of TE and TM polarization of symmetrical shape gratings
will be got.
Infrared scanning imaging system based on IR fiber bundle
Show abstract
In infrared scanning imaging system, long linear-array detector is needed for large field of view. Instead of using long
linear-array detector, we couple a non-conventional Infrared (IR) fiber bundle to a small scale Infrared Focal Plane Array
(IRFPA) whose format is 320×256 in system to implement 1024×4 format linear array imaging. The input of fiber bundle
is long linear array while output is plane-array. Fibers in IR fiber bundle are one to one mapping. Input end of fiber
bundle is set at the focal plane of telescopic objective in system, and output end is coupled to IRFPA by coupling lens.
By calibrating the position of each fiber in IRFPA, together with the mapping relationship between input and output of
fiber bundle, a look up table is established. With the table, we can reconstruct the line object image. According to the
scanning period of system, we can get the infrared scanning image.
A novel design of a high performance passive millimeter-wave imager for security
Show abstract
This paper describes a high performance of opto-mechanically scanned millimeter-wave imager for airport security.
It employs a crank-rocker mechanism to generate a high speed line scanning, which produces a horizontal FOV
(field of view) of 30°. Accompanied by a frame scanning mirror of ±18° in the vertical direction, it brings about a
two-dimensional scan of the scene of 146cm×75cm which is 1 meter away from the system. By this scanning
mechanism, we use a single channel of a 94GHz receiver to collect the radiation from a convex lens which acts as
the focusing element. Then the output of the receiver is passed to an A/D converter and is displayed on a
conventional PC. The new scanning arrangement meets these requirements and has been being developed into a high
performance, low-cost, and compact prototype system which hopefully will meet the present and future needs for
millimeter-wave and terahertz imaging.
Wavelet denoising of pulsed laser radar signals
Show abstract
Signal processing is pivotal to laser radar system. Information like range, target's signature, etc. can be obtained from the
processed laser signals. The received laser pulses for pulse laser radar are modeled. A wavelet filter is designed to
denoise the contaminated laser signals. For the given laser signals, the filter based on the combination of correlation and
thresholding is proposed. The gain of the filter is compared with the traditional thresholding method. It is shown that the
combination of the correlation and thresholding denoising method is more effective for the weak laser radar signal
processing compared with the traditional thresholding method.
Computational reconstruction of thermal infrared integral image based on modeling sensor physical effects
Show abstract
A thermal infrared(MWIR or LWIR) integral imaging(II) system is proposed for acquiring and displaying 3D surface
infrared emission radiance information of a real target. To intuitively analyze infrared integral image quality, we perform
the numerical simulation and reconstruction of thermal integral image based on the modeling of sensor physical effects.
Specifically, the 3D object with thermal infrared radiance texture is first focused into infrared elemental images by
combining the virtual model of infrared microlens array and the response characteristics of detector array. Further, the
displayed thermal elemental images are obtained by simulating main degradation factors including the spatial filtering
blur, sampling effects, and spatial-temporal noise involved in practical infrared sensor. Finally, the thermal infrared 3D
integral image is reconstructed by plane-plane reconstruction technique (PPRT) method based on the degraded elemental
images. Their simulation results are demonstrated and analyzed. To the best of our knowledge, this is the first time to
study thermal infrared II system and implement computational II reconstruction by considering thermal sensor physical
effects.
Infrared image enhancement based on the edge detection and mathematical morphology
Show abstract
The development of the un-cooled infrared imaging technology from military necessity. At present, It is widely
applied in industrial, medicine, scientific and technological research and so on. The infrared radiation temperature
distribution of the measured object's surface can be observed visually. The collection of infrared images from our
laboratory has following characteristics: Strong spatial correlation, Low contrast , Poor visual effect; Without color
or shadows because of gray image , and has low resolution; Low definition compare to the visible light image;
Many kinds of noise are brought by the random disturbances of the external environment. Digital image processing
are widely applied in many areas, it can now be studied up close and in detail in many research field. It has become
one kind of important means of the human visual continuation. Traditional methods for image enhancement cannot
capture the geometric information of images and tend to amplify noise. In order to remove noise and improve
visual effect. Meanwhile, To overcome the above enhancement issues. The mathematical model of FPA unit was
constructed based on matrix transformation theory. According to characteristics of FPA, Image enhancement
algorithm which combined with mathematical morphology and edge detection are established. First of all, Image
profile is obtained by using the edge detection combine with mathematical morphological operators. And then,
through filling the template profile by original image to get the ideal background image, The image noise can be
removed on the base of the above method. The experiments show that utilizing the proposed algorithm can enhance
image detail and the signal to noise ratio.
A novel scheme for simultaneous transmission of 10-Gb/s baseband and 20-GHz microwave signals in radio-over-fiber system
Show abstract
To simultaneously modulate and transmit 10-Gb/s baseband and 20-GHz microwave signals on a single wavelength
using single-sideband (SSB) modulation technique, a novel ROF scheme is proposed and verified by simulation. Based
on a Dual-Parallel Mach-Zehnder Modulator (DPMZM) the scheme can carry the microwave signal on the upper
sideband(USB) and the baseband signal on the lower sideband(LSB). It is to be seen from the simulated results that the
crosstalk between the signals with dual services is very small. By means of subcarrier-multiplexing (SCM) technique, the
optical 20-GHz microwave wave carrier is generated to carry 155-Mb/s baseband signal and 10-Gb/s baseband signal is
imposed on the original optical carrier via SSB modulation. The simulated results of BER and the eye diagram are
achieved separately. The signals with dual services are successfully transmitted over 50-km single-mode fiber.
Study on peak-seeking algorithm for wavelength in Fourier transform infrared spectrometer
Show abstract
In the progress of wavenumber traceability using polystyrene films, different peak-seeking algorithms are discussed in
this paper. Conclusion shows that in commonly used methods, spline method, center of gravity method and the second
derivative method, spline method is better than the others with simple algorithm and good agreement. It is strongly
recommended to use in practical for calibrating FTIR spectrometer.
High quality continuous-wave THz imaging at 2.53 THz
Show abstract
Low-resolution of terahertz (THz) imaging troubled its applications in the field of medical diagnosis
and security inspection. The continuous wave (CW) THz imaging system utilizing a pyroelectric
detector has been realized. The two crucial factors were analyzed in theory and verified in experiment;
a high-quality THz image with the resolution of 0.4mm was obtained by choosing suitable imaging
parameters. In our experiment the THz wave frequency of 2.53 THz, the spot size of 1.8 mm and the
step length of 250 μm were selected to achieve high quality THz image. We also image several samples
with different materials utilizing this system, and the results were very good.
Contamination effects on radiant cooler
Show abstract
The radiant cooler is used to cool optics and detectors to reduce signal noise in infrared (IR) telescopes. In-orbit
radiant cooler could be contaminated by excessive molecular, particulate and outgassing. The contamination can
change the emittance, solar absorptance and scattering of the surface of optical reflector and earth shield. The paper
calculates the effection of contamination on the thermal properties of radiant cooler. The working performance
degrades a lot when the optical screens are contaminated. Anti-contamination is emphasized for the radiant cooler
through design, manufacture, tests and flight procedure for quantitative applications of remote sensing data. Low
outgassing materials, reasonable outgassing channels and outgassing heaters are applied to the radiant cooler to
reduce the potential contaminants. The flight performance of the cooler meets with the design requirements.
THz spectroscopy and polarization of jade
Show abstract
A terahertz time-domain spectrometer is employed to study various properties of jade, including the
kind identification and polarization analysis. The characteristic absorption spectra and refractive index
of jade are obtained in the range of 0.2 to 2.6 THz. Studying the absorption spectra and the
transmission temporal THz waveform with two peaks, which were confirmed to be coming from
ordinary and extraordinary beams, respectively, and result in fake absorption features. A practical ways
are suggested to remove the fake absorption features and therefore the real absorption spectra of jade
which accurately indicate the information of the samples can be obtained.
Carrier relaxations in trap states of GaInNAs and HgCdTe thin films
Show abstract
Degenerate pump-probe experiments have been performed with HgCdTe and GaInNAs thin films. The differential
transmission versus probe delay time shows a negative value for both films, indicating photoinduced absorption from the
trap states. After the negative minimum the differential transmission resumes to zero with long time constants. A rate
equation formalism has been employed to model the carrier dynamics. The calculations fit the experimental differential
transmission very well. The extracted time constants show that the carriers in the trap states of GaInNAs decay to the
equilibrium state with a single time constant of 1.2 ns, while those in HgCdTe shows two time constants of 0.9 ns and 13
ps, respectively. This implies that there exist two types of deep level traps, fast and slow, in HgCdTe thin films.
Study of atmospheric pollution using terahertz wave
Show abstract
Terahertz time-domain spectroscopy (THz-TDS) is a new coherent spectral technique. In this
paper the spectral characteristics of air pollution gas, sulfur dioxide and hydrogen sulfide, had
been measured with THz-TDS in the range of 0.2-2.6THz. The result shows that both the gases
have equi-spaced absorption peaks and different gases have different intervals. We also
investigated the influence of pressure on absorption spectrum by changing the pressure of the
gases in a chamber. The experimental results indicate that the absorption peaks become
sharper with increasing the pressure. Our experiments prove that terahertz Time-Domain
Spectroscopy technique should be a powerful candidate for detecting atmospheric pollutants.
Terahertz imaging technique and application in large scale integrated circuit failure inspection
Show abstract
Terahertz ray, as a new style optic source, usually means the electromagnetic whose frequencies lies
in between 0.1THz~10THz, the waveband region of the electromagnetic spectrum lies in the gap between microwaves and
infrared ray. With the development of laser techniques, quantum trap techniques and compound semiconductor techniques,
many new terahertz techniques have been pioneered, motivated in part by the vast range of possible applications for
terahertz imaging, sensing, and spectroscopy. THz imaging technique was introduced, and THz imaging can give us not
only the density picture but also the phase information within frequency domain. Consequently, images of suspicious
objects such as concealed metallic or metal weapons are much sharper and more readily identified when imaged with
THz imaging scanners. On the base of these, the application of THz imaging in nondestructive examination, more
concretely in large scale circuit failure inspection was illuminated, and the important techniques of this application were
introduced, also future prospects were discussed. With the development of correlative technology of THz, we can draw a
conclusion that THz imaging technology will have nice application foreground.
A Thz modulator use the photo-carrier surface plasma effect
Show abstract
A design of light modulator for THz amplitude and phase modulations has been presented in this paper.
Simplest versus of the Drude model is adopted, in which the collision damping is independent of the carrier
energy. In our experiment, we use THz-TDS as THz source and detector. A laser whose wavelength is
808nm was used to irradiate the intrinsic Si(high-resistance), so as to let it generate the Photo-carriers ,and
to influence the conductance . The Photo-carriers will change the absorption coefficient of the THz wave
and also influence the dielectric of the sample, hence to control the characteristics of the THz wave in the
silicon . By changing the light intensity , due to the different photon-generated carrier concentration ,the
single transmission of the THz wave in the silicon wafer sample is changing remarkable . Theoretically,
the modulation depth can be more than 80%. we present our design of light modulator for THz, and show
the Digital simulation of our design. Also, according to this design theory, Optical/electronic integrated
modulation of THz can be realized, that will be our future work.
Excitonic optical absorption in quantum wells under intense terahertz waves polarized along the grown direction
Show abstract
Excitonic optical absorption in quantum wells (QWs) under intense terahertz (THz) waves polarized along the
grown-direction is investigated. The characteristics induced by the strong THz field in the optical absorption
spectrum in the QWs near the band gap edge is analyzed by coherent wave approach. The calculated results
with and without the presence of THz field are presented. It shows that the excitonic absorption peaks may split
or broaden when an intense THz field is applied. The presence of an intense THz field results in the formation
of replicas in the absorption spectrum. The replicas are not symmetric and presence on both sides of the main
excitonic peaks due to the Coulomb interaction between electrons and holes.
Experimental study on the electro-optic effect of crystals in the terahertz range
Show abstract
In this paper, the electro-optic effect of the crystals was observed and discussed in the terahertz range, and
theoretic analysis was implemented on the experiment's feasibility. Three crystals, ZnTe, GaAs and Si were chosen as the
experimental group in the research, and the way to use terahertz TDS system properly to measure the spectrum changes
of refractive indexes of crystals under voltage 0-200 V with 10 cm distance in terahertz range is demonstrated. According
to the measurements, the refractive index of GaAs had obvious changes around 0.0932 in the frequency from 800 GHz to
2 THz, the refractive index of ZnTe has comparatively small changes around 0.015, and the refractive index of Si hardly
changes. The results have validated that the refractive indexes of electro-optic crystals ZnTe and GaAs have changed as
the intensity of the external electric fields varied appropriately. And that may have potential applications in photoelectric
devices in the terahertz range. Both theoretic analysis and experimental results demonstrate the experimental study is
reasonable and successful.
Thermodynamic character of fiber array visible to infrared image transducer
Show abstract
A technique of fiber array structure of visible to infrared image transducer for infrared imaging control and guide was
discussed. Be different from the normal fiber array, the structure here is micro-fabricated on quartz glass covered with
visible absorb member in front of the fiber. The fiber array structure works in vacuum and cooling chamber. The 3D
model of fiber array structure for finite element analysis based on the secondary radiation was established. The material
parameter, including density, specific heat and thermal conductivity, and the structure size including section size, length
of fiber array transducer for temperature and time character were studied. The simulation results show that the thermal
conductivity and length of fiber array are key parameters for transducer's property, and the optimized parameters for
fiber array structure transducer were given. The fiber array structure of visible to infrared image transducer has the
advantage of higher spatial and temperature resolution, and less manufacture cost. The optimized parameter for fiber
array visible to infrared image transducer can reach the frequency of 100Hz and higher temperature of 250°C in case of
increasing impulse power which can be used as infrared scene projector in hardware-in-the-loop simulation experiment.
Sideband separating mixer for 600-720 GHz
Show abstract
The ALMA Band 9 receiver cartridge (600-720 GHz) based on Dual Sideband (DSB) superconductor-insulatorsuperconductor
(SIS) mixer is currently in full production. In the case of spectral line observations, the integration time
to reach a certain signal-to-noise level can be reduced by about a factor of two by rejecting an unused sideband. The goal
is to upgrade the current ALMA band 9 cartridge to a full dual-polarization sideband separating (2SB) capability, with
minimal-cost upgrade path. A new compact and modular sideband separating mixer was designed, and a prototype
manufactured. The individual SIS mixer devices in the 2SB block are implemented as conventional Band 9 DSB mixers,
so that existing devices can be reused and tested individually. Any ALMA DSB developments contribute to the 2SB
upgrade. The first experimental results demonstrate noise temperature from 300K to 500K over 80% of the band, which
will be improved to fit the ALMA requirements. Nevertheless, the frequency response for 2SB is the same as for DSB,
showing that the RF design is still valid, even with different SIS mixer devices. The quality of the RF and IF design is
confirmed by a sideband rejection ratio of about 15 dB, which is within the ALMA spec (>10dB ).
Abnormal enhancement of terahertz signal by using a hole
Show abstract
Huygens-Fresnel principle and half-wave method are usually used to explain the diffraction effect as the
light passing through a hole. We present a new simple method to enhance the terahertz signal intensity by
using a small hole. We found that in the terahertz time-domain spectroscopy, the terahertz signal
enhances by 13.87% as a hole with certain size is put in a certain position of the terahertz beam path.
This effect can be fully explained by using Huygens Fresnel principle. Therefore, in the condition of
terahertz emitter and detector are unchanged, by using this method to enhance the terahertz signals is of
great significance.
Air-core terahertz fiber with high birefringence
Show abstract
In this paper, we propose an efficient air-core Terahertz (THz) fiber with high birefringence and low modal absorption
loss. The photonic crystal fiber has a triangular-lattice with circular subwavelength air-holes in the microstructured
cladding and elliptical subwavelength air-holes in the core. In this structure, the effective index of the core is above that
of the cladding, which leads to a better confinement of the field and ensures the low loss characteristic for THz guiding.
With elliptical air-holes in the core, the proposed THz fiber exhibits high birefringence. The background medium is the
polymer material with low absorption in THz region. The proposed design has been simulated based on the finite
element method with anisotropic perfectly matched layers (PML) absorbing boundary condition. Numerical simulations
show that with a moderate ellipticity of the elliptical air-holes in the core region, the proposed THz fiber can exhibit high
birefringence on a level of 10-2 in a 0.2THz to 2.0THz frequency range. And the THz fiber's guiding loss caused by
material absorption can be reduced effectively by the addition of more air holes in the core region.
Easy robot programming for beginners and kids using augmented reality environments
Show abstract
The authors have developed the mobile robot which can be programmed by command and instruction cards.
All you have to do is to arrange cards on a table and to shot the programming stage by a camera. Our card
programming system recognizes instruction cards and translates icon commands into the motor driver
program. This card programming environment also provides low-level structure programming.
Iterative restoration algorithms for improving the range accuracy in imaging laser radar
Show abstract
Scannerless imaging laser radar has been a focus of research in these years for its fast imaging speed and high resolution.
We introduced a three-dimensional imaging laser radar using intensified CCD as the receiver with constant gain and line
modulated gain. The distance map of a scene is obtained from two intensity images. According to the transmission
characteristics of the imaging system, a model of degeneration of the gray images is established and the range accuracy
of imaging laser radar based on this model is analyzed. The results show that the range accuracy is related with the
reflectivity, the actual distance and some other factors on the fast-distance-varying region, while it is mainly concerned
with shot noise for the flat area. On the basis of the cause of measurement error and the distribution characteristics of
noise, a method which uses iterative restoration algorithms on obtained intensity images is presented, Simulation is
carried out and the results show that root mean square error of distance map obtained with this method is decreased by
50%, compared with the distance map obtained by measurement. Finally the restoration results of radar images are
demonstrated to verify the effectiveness of this method.
Large focal depth of THz imaging system based on quasi-Bessel beams
Jianjun Liu,
Lifeng Wang,
Jing Li,
et al.
Show abstract
THz imaging technology will be potentially used in structure's defects detection, package inspection, on line product
quality control, security screening or other nondestructive testing fields. But due to its long wavelength, it is difficult to
obtain high spatial resolution and large focal depth simultaneously for conventional imaging systems. In this paper,
diffraction free quasi-Bessel beams are used in THz imaging system to enhance the focal depth with high spatial
resolution. PE conical lenses were designed and fabricated to generate quasi Bessel beams. Numeric simulations
demonstrated that with suitable parameters of the conical lens, the diffraction free propagation distance and effective
focal depth of the imaging system are easily reached up to 165mm, 100mm, respectively. A THz imaging system based
on quasi-Bessel beams was established, and results were in good agreement with simulations. Furthermore, the inner
defects built-in artificially in phenolic foam samples with diameter of 0.4mm were figured out successfully.
Carrier dynamics of doped silicon measured by femtosecond pump-terahertz probe spectroscopy
Show abstract
The carrier dynamics and terahertz photoconductivity in the n-type silicon (n-Si) as well as in the p-type Silicon (p-
Si) have been investigated by using femtosecond pump-terahertz probe technique. The measurements show that the
relative change of terahertz transmission of p-Si at low pump power is slightly lower than that of n-Si, due to the lower
carrier density induced by the recombination of original holes in the p-type material and the photogenerated electrons. At
high pump power, the bigger change of terahertz transmission of p-Si originates from the greater mobility of the carriers
compared to n-Si. The transient photoconductivities are calculated and fit well with the Drude-Smith model, showing
that the mobility of the photogenerated carriers decreases with the increasing pump power. The obtained results indicate
that femtosecond pump-terahertz probe technique is a promising method to investigate the carrier dynamics of
semiconductors.
Analysis of scattering and polarization characteristics of chiral sphere with a large-size parameter
Show abstract
Based on the spherical vector wave functions, we research the scattering of a homogeneous chiral sphere to a plane wave.
The expansion coefficients of scattered fields and internal fields are obtained through the boundary condition at the
sphere interface. The logarithmic derivatives of Ricatti-Bessel functions are introduced in order to avoid the numerical
overflow of high-order terms or larger argument spherical Bessel function and the problem of the accumulative error in
the matrix calculation. Thus, the scattering characteristics of a chiral sphere with larger size parameter can be studied
numerically. Moreover, the influence of chiral parameter on the polarization properties is also numerically analyzed.
A total variation denoising algorithm for hyperspectral data
Show abstract
Since noise can undermine the effectiveness of information extracted from hyperspectral imagery, noise reduction is a
prerequisite for many classification-based applications of hyperspectral imagery. In this paper, an effective three
dimensional total variation denoising algorithm for hyperspectral imagery is introduced. First, a three dimensional
objective function of total variation denoising model is derived from the classical two dimensional TV algorithms. For
the consideration of the fact that the noise of hyperspectral imagery shows different characteristics in spatial and spectral
domain, the objective function is further improved by utilizing two terms (spatial term and spectral term) and separate
regularization parameters respectively which can adjust the trade-off between the two terms. Then, the improved
objective function is discretized by approximating gradients with local differences, optimized by a quadratic convex
function and finally solved by a majorization-minimization based iteration algorithm. The performance of the new
algorithm is experimented on a set of Hyperion imageries acquired in a desert-dominated area in 2007. Experimental
results show that, properly choosing the values of parameters, the new approach removes the indention and restores the
spectral absorption peaks more effectively while having a similar improvement of signal-to-noise-ratio as minimum
noise fraction (MNF) method.
THz/sub-THz narrow-gap semiconductor detector
Show abstract
Direct detection mm/sub-mm wave warm-carrier bipolar narrow-gap Hg1-xCdxTe semiconductor bolometers
that can be used as picture elements in THz sensitive arrays, are considered. The response of Hg1-xCdxTe warm-electron
bolometers was measured in v=0.037-1.54 THz frequency range at T=68-300 K. Bipolar semiconductor warm-electron
bolometer theoretical model was developed. In the detector considered the electromagnetic wave propagates in
semiconductor waveguide, heats electrons and holes, creates their excess concentrations, as well as, the electromotive
forces. These effects cause the bolometer response voltage. Experimental results confirm the model main conclusions.
Because of response time defined by carrier recombination time in HgCdTe layers (τ~10-8-10-6 s) and the noise
equivalent power that can reach NEP300 K~4×10-10 W/Hz1/2 in mm-wave region, the arrays on the base of HgCdTe
bolometers can make them promising for active relatively fast frame rate sensitive applications. At liquid nitrogen
temperature NEP can lowering up to NEP77 K~10-11 W/Hz1/2. Embeded p-n-junctions in HgCdTe can increase the
detectors responsivity by an order.
Application of millimeter-wave photonics technology in passive millimeter-wave imaging
Yuedong Zhang,
Yuesong Jiang,
Jingping Guo,
et al.
Show abstract
Passive millimeter-wave imaging is attractive due to the ability to obtain images in low-visibility conditions. In this
paper, a passive millimeter-wave imaging method using photonic processing is presented. The principle of the
millimeter-wave photonic signal processing method is described. The relationship between the signal conversion gain
and the component parameters is discussed. The noise characteristic of this detection method is analyzed. A millimeterwave
radiometer using photonic processing is presented in this paper. A passive millimeter-wave scanning imaging
system using this processing method was implemented. The imaging experiment results show that this imaging method
is effective.
Temperature measurement of contact resistance based on infrared detection
Show abstract
For science and technology, the level of science and technology is determined by the measurement accuracy and
efficiency to some extent. Contact resistance can not be ignored in precise measurement. Because the measured object is
not directly contacted with infrared measurement device, there is no friction. Infrared measurement has the advantage of
high sensitivity, fast response and so on. In this paper, the reasons for the temperature rising of the contact resistance and
its harm and the importance of measuring the temperature of the contact resistance in precise measurement are analyzed
firstly; then some theories of the infrared detection technology are introduced; finally, an infrared temperature
measurement system based on SCM is designed.
The observation of terahertz spectra of all-trans beta-carotene molecule
Jian Zuo,
Liangliang Zhang,
Fei Yu,
et al.
Show abstract
The carotenoid molecules associated with the proteins perform the important physiological functions of harvesting,
transferring and dissipating light energy in the light-harvesting process. Especially, these functions originate from
changes in the electronic and molecular configurations of the carotenoid molecules under the influence of intermolecular
or intramolecular interactions with the apo-protein. Terahertz spectroscopy is a power tool for the prediction of the
configuration or conformation of the carotenoid and non-covalent interactions. All-trans beta-carotene molecule has
eleven conjugated double bonds in the polyene chain with all-trans configuration. In this paper, the low-frequency
vibrations of all-trans beta carotene molecule were firstly observed. One hand, the vibrational modes of 0-3 THz were
obtained by terahertz time-domain spectroscopy (THz-TDS) and Fourier transform far-infrared (FT-FIR) spectrometer,
respectively. The absorption spectrum of all-trans beta-carotene molecules were also presented in this frequency region.
On the other hand, the other vibrational modes in the range of 3-20 THz were only obtained through FT-FIR
spectrometer. There exhibit a lot of rich and distinct vibrational peaks. The terahertz spectra of all-trans beta-carotene
molecules represent unique fingerprints of the molecular geometries structures of both beta-ionone and long conjugated
double bonds. And the environment of the molecule leads us to the conclusion that THz technique can be used for the
recognition of the organic molecules and their conformations.
Continuous wave terahertz phase imaging
Show abstract
Continues wave terahertz imaging has been used widely in the field of security inspection and nondestructive
examination because of its simplicity and stability. In this presentation, we proposed an image method with continues
wave terahertz interferometry to obtain the sample's phase information. In the experiment, a reference terahertz beam
was added into the exiting continues wave terahertz imaging system to be a Michelson interferometer. With three maps
obtained at three fixed phase-shift positions, a phase image is obtained by using a phase shift algorithm. Afterwards, this
phase image is unwrapped to get its accurate phase profile. By this method, a bulk of foam with two height steps
structure is imaged. The result shows that the inner structures of samples can be identified clearly and the relative optical
depth profiles of samples can be obtained.
Transient surface photoconductivity of GaAs emitter studied by terahertz pump-emission spectroscopy
Show abstract
The ultrafast carrier dynamics and surface photoconductivity of unbiased semi-insulating GaAs have been investigated in
detail by using terahertz pump-emission technique. Through theoretical modeling based on Hertz vector potential, it is
found that transient photoconductivity plays a very important role in the temporal waveform of terahertz radiation pulse.
Anomalous enhancement in both terahertz radiation and transient photoconductivity is observed subsequent to the
excitation of pump pulse, and our modeling gives successful analyses for the dynamics of photogenerated carriers in the
GaAs. We attribute these phenomena to carrier capture in the EL2 centers. Moreover, the pump power- and temperaturedependent
measurements are also performed to verify this model.
Slow light in the dielectric-loaded metallic waveguide for terahertz wave
Show abstract
The modes in a metallic waveguide loaded with a high permittivity dielectric rod may possess similar dispersion
relations to the modes in the left-handed metamaterial (LHM) waveguide. Therefore, such dielectric-loaded metallic
waveguide may also support slow light propagation. The slow light in such waveguide is numerically studied. The
properties and the existence conditions of slow light modes in such waveguide are also numerically studied. The results
show that the wavelength of slow light varies with the parameters of the waveguide and that high-contrast between the
dielectric rod and the air is necessary of existence of slow light modes. The linearly tapered waveguide are proposed
accordingly to realize the "trapped rainbow" phenomena. The practical tapered lossy waveguide is also investigated. It is
shown that the slow light with low loss can be achieved in a realistic waveguide. Moreover, a novel notch filter based on
such slow light waveguide is proposed.
Terahertz difference frequency generation in GaSe from a doubly-resonant walk-off compensated KTP OPO
Show abstract
We have achieved a Terahertz (THz) DFG system based on a walk-off compensated intracavity pumped dualwavelength
KTP OPO employing two identical KTP crystals. The KTP OPO is doubly resonant and works near the
degenerate point at 2.128μm, which doubles the quantum efficiency compared with DFG using pump pulses around 1μm.
This THz source is simple and compact, about 10×10×40cm2 in size. Besides lower threshold and better stability, the
walk-off compensated KTP OPO greatly improves the pump beam quality and enhances the DFG conversion efficiency.
With an 8-mm-long GaSe crystal, the generated THz tuning range is from 0.186THz to 3.7THz with the maximum
output voltage of 489V on the bolometer at 1.68THz. An average enhancement of 76.7% for the THz energies is realized
using the walk-off compensated KTP OPO than a common one. The conversion efficiency can be improved with a
longer and better GaSe crystal.
Theoretical study on the generation of THz sub-comb via surface-emitted optical rectification of ultra-short pulse in periodically poled lithium niobate
Show abstract
In this paper, we proposed a method for THz sub-comb generation based on optical rectification. The result of our
calculation indicated that THz pulse train, generated by surface-emitted optical rectification (OR) of femtosecond (fs)
laser pulse in a periodically poled lithium niobate (PPLN), has a comb-like spectrum. The theoretical analysis was based
on radiating antenna model. The characteristic of this THz sub-comb was analyzed both in frequency and time domain.
The mechanism of this phenomenon was explained both by spectral interference between early and late pulses and by
high-order quasi phase matching. THz sub-comb generated by this method can cover a large bandwidth and have a wide
free spectral range.
Low-loss and birefringent terahertz polymer elliptical-tube waveguides
Show abstract
In this work, modal birefringence and loss characteristic for the fundamental mode in terahertz (THz) polymer
elliptical-tube waveguides are investigated by using a full vector finite element method (FEM). Numerical results show
that this kind of waveguide has high birefringence (~10-2) and better loss property as a large part of mode power is
trapped in the air-core inside the polymer elliptical-tube. Dependence study of the birefringence on several parameters is
also provided and numerical results show the birefringence increases as refractive index and thickness of polymer tube
increased.
The guidance mechanism and numerical simulation of THz polymer hollow-core photonic crystal fiber
Show abstract
With the development of terahertz (THz) technology, an efficient propagation waveguide is essential for the construction
of compact THz devices. Hollow core photonic crystal fiber with a large air core at the center and a cladding formed by a
periodic arrangement of polymer tubes has been demonstrated in this paper. The guidance mechanism is based on
anti-resonant reflection from struts of solid material in the cladding. Since most electromagnetic field is dominated in the
air core, hollow core fibers have obvious advantages in lower absorption. The propagation characteristics of the fiber,
such as the mode field distribution and the loss coefficient are numerically investigated through the finite element
method. The result shows that an effective way to reduce the absorption is to enlarge the central air core and reduce the
overlap between the field and material.
Study on the generation of high-power terahertz wave from surface-emitted THz-wave parametric oscillator with MgO:LiNbO3 crystal
Show abstract
High-power nanosecond pulsed THz-wave radiation was achieved via a surface-emitted THz-wave parametric oscillator
(TPO). The effective parametric gain length under the condition of noncollinear phase matching was calculated to
optimize the parameters of the TPO. Only one MgO:LiNbO3 crystal with large volume was used as gain medium.
THz-wave radiation from 0.8 to 2.9 THz was obtained. The maximum THz-wave output was 289.9 nJ/pulse at 1.94 THz
when pump power density was 211 MW/cm2, corresponding to the energy conversion efficiency of 3.43×10-6 and the
photon conversion efficiency of about 0.05%. The far-field divergence angle of THz-wave radiation was 0.0204 rad at
vertical direction and 0.0068 rad at horizontal direction.
Research on thermal characteristics of electronic devices using thermal microscopes
Show abstract
Electronic devices are widely used in various industries, their temperature distribution cannot be obtained by traditional
test methods. In recent years, simulation softwares are used to simulate the thermal characteristics of electronic devices
and play a positive role on the reliability improvement, on the contrast, their validity cannot be verified. In this paper, the
chip temperature rise process is simulated by ICEPEAK software. Some factors that change thermal characteristics are
analyzed. The actual working temperature obtained by the thermal microscope is compared with the simulation
temperature. The validity of simulation temperature is tested and the relation is built between the actual temperature and
simulation temperature. Finally, it is pointed that thermal microscopes are the development direction on the electronic
devices design and reliability testing.
The separation for simultaneous transmission of baseband and microwave signals in a radio-over-fiber system
Show abstract
Simultaneous generation and transmission of 10-Gb/s baseband signal and 20-GHz microwave signal with 155-Mb/s
on-off-keying (OOK) data on a single wavelength over 50-km-long fiber link based on a dual-parallel Mach-Zehnder
modulator (DPMZM) are investigated. After simultaneous modulation of the baseband signal and microwave signal at
central office (CO), the hybrid signals are separated by interleaver(IL) or fiber Bragg grating (FBG) at base station (BS).
The center wavelength spacing and bandwidth of IL, also the reflection ratio, center wavelength and bandwidth of FBG
are to be considered carefully as the baseband and microwave signal are only tens of GHz spacing and hard to be
separated with each other. Through theoretical analyses and simulation, for the demonstrated hybrid transmission system,
the relations of Q factor with the reflection ratio and bandwidth of FBG are analyzed separately in different fiber links
(SMF and DSF).
Analysis of quantitative differences in large-aperture size for free-space optical communication systems with circle polarization shift keying and on-off keying in atmospheric turbulence channels
Show abstract
A theoretical model is proposed to study quantitative differences in the size of large-aperture between circle polarization
shift keying (CPolSK) and on-off keying (OOK). The quantitative differences can be analyzed with the impact from
atmospheric condition, link length, and communication wavelength. Numerical results show that FSO CPolSK systems
with longer communication wavelength can reduce the size even smaller than the systems using OOK, while it can be
not obvious with increasing link length. Meanwhile, increasing average signal-to-noise ratio (SNR) leads to a reduction
of the difference in aperture size. These results can be helpful for FSO systems design.
Modeling and measurement of IF gain bandwidth and intrinsic noise temperature for NbTiN hot electron bolometer mixers at Terahertz frequencies
Jiang Ling,
Fei Liu Yun,
Satoshi Yamamoto
Show abstract
In this paper, we present the modeling and measurement results of niobium titanium nitride hot electron bolometer
mixers with different sizes at terahertz frequencies. A distributed hot spot model which is based on solving a heat
balance equation is employed to characterize current-voltage curve, electron and phonon temperature distribution along
superconducting microbridge, intermediate frequency gain bandwidth and intrinsic noise temperature of the mixers. The
simulated intermediate frequency gain bandwidth decreases with the increase of microbridge length, which is in good
agreement with measured results. A difference of factor of several tens exists between the calculated and measured mixer
noise temperature, which is probably due to the disfigurement of waveguide structure and unknown noise from the mixer.
Positive and negative metamaterials as frequency selective surface
Show abstract
We study theoretically that a resonant response with a high quality factor could be achieved in a planar positive or
negative metamaterials by weakly breaking the geometrical symmetry of its unit cells. The trapped mode resulting from
broken structures is investigated using the finite element method and the dependence of the quality factor on structural
parameters is also discussed.
A Radio-over-fiber system with 64-QAM photonically generated orthogonal frequency divsion multiplexing signals
Show abstract
We have proposed and investigated a radio-over-fiber (ROF) system transmitting 100Gb/s orthogonal frequency division
multiplexing (OFDM) signals by simulation. The ROF system can transmit vector modulation formats, such as OFDM
signal. The simulation results show that carrier suppression technique can be used to achieve two 50Gb/s OFDM signals
over 20km SMF successfully.
Quantitative analysis of Ni, Zr and Ba in soil by combing neuro-genetic approach and laser induced breakdown spectroscopy
Show abstract
With the combination of neuro-genetic approach and laser-induced breakdown spectroscopy (LIBS), an improved
method is proposed to predict the concentrations of Ni, Zr and Ba in soil samples. In this method, an artificial neural
network (ANN) based on gradient descent with momentum and adaptive learning rate back propagation (GDMABP)
algorithm is used. Simultaneously, an optimization strategy based on genetic algorithm (GA) is employed for selecting
number of neurons in hidden layer and momentum coefficient in GDMABP ANN and to obtain an optimized network.
Subsequently, the network is used to predict concentration of Ni, Zr and Ba from the tested LIBS data. The approach of
neuro-genetic for LIBS analysis is described in detail. The predicted results are compared with those obtained from
conventional calibration curve method. Overall, the method of combining neuro-genetic approach with LIBS is capable
of predicting elemental concentration.
Noncontact ultrasonic excitation thermography inspection technique
Show abstract
Conventional ultrasonic thermography (thermosonic or sonic infrared imaging) is a technique in which acoustic energy is
coupled to the structure by means of an acoustic transducer in contact with the sample, the captured temperature at the
defect areas by an infrared camera is relatively higher than that of the surrounding area. The primary problem of this
technique is that the acoustic horn must be mechanically in contact against the tested sample with an applied force.
Therefore, the potential for damaging the structure especially for the filmy, brittle and fragile structure can't be ignored.
In this paper, a new NDE technique based on a non-contact ultrasonic excitation thermography has been presented. The
technique utilizes a redesigned ultrasonic horn to excite the sample in a non-contact fashion, and an infrared camera to
monitor the variation of the surface temperature. The presented experimental results show that the non-contact ultrasonic
excitation thermography has some potential in NDE application.
Study on the symmetric line-laser rut measurement
Hongxun Song,
Cui Fang
Show abstract
The rut results based on the line-laser rut measurement are often subjected to the vehicle bumps, vehicle pitch changes
in practical applications. The principle of line-laser rut measurement is described and the factors are analyzed from the
perspective of optical imaging. A new method of symmetrical line-laser rut measurement is proposed. This method uses
symmetric line-laser imaging system and can effectively reduce the rut test errors caused by the vehicle bumps, vehicle
pitch changes. Experimental results show that the symmetric line-laser rut measurement can be used to detect road
surface rut.
Study on the symmetrical laser displacement sensor for the road surface measurement
Hongxun Song,
Ronggui Ma,
Yi Zhang,
et al.
Show abstract
The asymmetry imaging spot caused by the CCD saturation and the scattering of uneven road surface usually leads to
lower accuracy in the road surface detection. A new method of the symmetric displacement sensor for the road
measurement is given. The sensor consists of two symmetrical image systems and two line scan CCDs which are
arranged reversely. The centroidal algorithm is adept to calculate the coordinates of the image point of each CCD. The
finial displacement is given by the average of the coordinates of the image point of two CCDs. The experimental results
indicate that the symmetrical laser displacement sensor can reduce the asymmetry imaging test error and improve the
precision of measurement effectively. It is very suitable for the pavement evenness, rut and texture detection.
Preliminary study on quality evaluation of pecans with terahertz time-domain spectroscopy
Show abstract
This paper reports a preliminary work on a feasibility study of applying terahertz (THz) technology for pecan quality
evaluation. A set of native pecan nuts collected in 2009 were used during the experiment. Each pecan nutmeat was
manually sliced at a thickness of about 1mm, 2mm, and 3mm and a size of about 2cm (length) ×1cm (width). Pecan
shell and inner separator were also cut into the same size. The absorption spectra for the nutmeat slices, shell, and inner
separator were collected using a THz time-domain spectroscopy (THz-TDS) developed by a group of researchers at
Oklahoma State University. The test results show that nutmeat, shell, and inner separator had different absorption
characteristics within the bandwidth of 0.2-2.0 THz. To study the capability of insect damage detection of the THz
spectroscopy, the absorption spectra of insects (living manduca sexta and dry pecan weevil) were also collected. Due to
high water contents in the insects, very obvious spectral characteristics were found. The results from the preliminary
study show a potential of THz technology applied for quality detection of bio-products. However, since bio-products
mostly have high water content and are handled under an environment with certain levels of water content, practical
issues needs to be further investigated to make the THz technology a feasible tool for quality evaluation.
Advanced one-dimensional triple wavelet analysis in row for infrared images from un-cooled infrared MEMS system
Show abstract
For the limitation of detecting materials, the images from the novel un-cooled infrared system based on visible light
readout are blurry and have low contrast. The images also have more noise and larger holes. Especially after
pseudo-color processing, the noise and holes will become much clearer. For the characteristics of images in the
un-cooled IR system, the traditional image processing methods for IR images are not suitable for the image in our
research. Therefore, an advanced one-dimensional triple wavelet analysis in row for infrared images is presented based
on the characteristics of un-cooled infrared system. In this method, the triple wavelet decomposition is made in each row
of image, and detail coefficients and approximation coefficients of each row can be obtained. The detail coefficients in
the first time of wavelet decomposition express the whole details of image containing noise and the edge of object. So
after low-pass filter, the noise in the image can be suppressed. By the wave reconstruction made between the
approximation coefficients in triple wavelet decomposition and the detail coefficients after low-pass filter, each row in
images without noise and holes can be gained. In wavelet reconstruction, a weight being proportional with the filtering
window is multiplied with detail coefficients. The weight can make sure the gray value of whole picture and the contrast
cannot be lower after low-pass filter. The images from un-cooled infrared system are processed in the computer with the
software of MATLAB. The results support that compared with traditional methods the novel method can be more
effective to eliminate the noise and fill holes, and better response to the temperature details of objects.