Show all abstracts
View Session
- Front Matter: Volume 9102
- THz Imaging
- THz Sources I
- THz Detection
- THz Sources II
- Novel Concepts and Applications I
- Keynote Session
- Novel Concepts and Applications II
- Poster Session
Front Matter: Volume 9102
Front Matter: Volume 9102
Show abstract
This PDF file contains the front matter associated with SPIE Proceedings Volume 9102, including the Title Page, Copyright information, Table of Contents, Invited Panel Discussion, and Conference Committee listing.
THz Imaging
Image reconstruction method for non-synchronous THz signals
Show abstract
Image reconstruction method for non-synchronous THz signals was developed for a combination of THz Free Electron
Laser (THz-FEL) developed by Osaka University with THz imager. The method employs a slight time-difference
between repetition period of THz macro-pulse from THz-FEL and a plurality of frames for THz imager, so that image
can be reconstructed out of a predetermined number of time-sequential frames. This method was applied to THz-FEL
and other pulsed THz source, and found very effective. Thermal time constants of pixels in 320x240 microbolometer
array were also evaluated with this method, using quantum cascade laser as a THz source.
Peculiarities of the detection and identification of substance at long distance
Show abstract
Nowadays, the detection and identification of dangerous substances at long distance (several meters, for example) by
using of THz pulse reflected from the object is an important problem. In this report we demonstrate possibility of THz
signal measuring reflected from investigated object that is placed before a flat metallic mirror. A distance between the
flat mirror and the parabolic mirror this mirror is equal to 3.5 meters. Therefore, at present time our measurements
contain features of both transmission and reflection modes. The reflecting mirror is used because of weak average
power of used femtosecond laser. Measurements were provided at room temperature and humidity about 60%. The aim
of investigation was the detection of a substance in real condition. Chocolate and Cookies were used as samples for
identification.
We also discuss modified correlation criteria for the detection and identification of various substances using pulsed THz
signal in the transmission and reflection mode at short distances of about 30-40 cm. These criteria are integral criteria in
time and they are based on the SDA method. Proposed algorithms show both high probability of the substance
identification and a reliability of realization in practice.
We compare P-spectrum and SDA- methods in the paper and show that P-spectrum method is a partial case of SDAmethod.
Initial results of a real-time, quad-frequency, polarization-sensitive THz line camera
Show abstract
We have developed a cost-effective, quad-frequency band THz imager for real-time THz imaging applications operating
at 220GHz, 320GHz, 420GHz, and 520GHz frequency bands. The new sensor is based on antimonide-based
heterostructure backward diodes impedance matched and monolithically integrated with high-gain, narrowband planar
antennas. The antennas are dual-linearly polarized to allow direct measurement of beam polarization. This paper details
the fabricated THz detector array and the high-speed, low-noise readout electronic chain. Experimental results on the
performance of the readout chain and simulations of the expected THz detector performance are presented.
3D THz range finder of concealed objects
Show abstract
Numerous applications require fast and accurate range measurement of concealed objects. As THz waves penetrate
almost all materials except metals, they are a candidate to perform this task. In this paper a system consisting of an
illumination THz source and a THz detector array is presented.
A solid state 300GHz THz source signal is frequency modulated and guided to a detector array using a beam splitter. The
detector array consists of ultra-sensitive bolometers with 1000V/W sensitivity and NEP of 5pW/√Hz. Their square law
sensitivity characteristic allows mixing of the reflected wave with the illumination wave, resulting in a mixed product
with a difference frequency of few kHz proportional to the target distance, the frequency modulation span, and its rate.
Parallel signal processing of all 16 signals results in fast range detection of the target. All 16 detectors provide four
readings per second for all X and Y positions of the image. A compact and portable system with 40GHz frequency
modulated source provides Δf/Δt = 160GHz/sec. This corresponds to a 1kHz difference frequency per one meter distance
of the target. A resolution accuracy in the micrometer range has been achieved using advanced signal processing.
In the paper the processing algorithms and the obtained results are presented and discussed. The complete hardware
structure of the system is described together with the required signal processing procedures. The advantage of the
presented system is that it operates at room temperature and is therefore cost effective and very robust.
Approaching real-time terahertz imaging using photo-induced reconfigurable aperture arrays
Show abstract
We report a technique using photo-induced coded-aperture arrays for potential real-time THz imaging at roomtemperature.
The coded apertures (based on Hadamard coding) were implemented using programmable illumination on
semi-insulating Silicon wafer by a commercial digital-light processing (DLP) projector. Initial imaging experiments
were performed in the 500-750 GHz band using a WR-1.5 vector network analyzer (VNA) as the source and receiver.
Over the entire band, each array pixel can be optically turned on and off with an average modulation depth of ~20 dB
and ~35 dB, for ~4 cm2 and ~0.5 cm2 imaging areas respectively. The modulation speed is ~1.3 kHz using the current
DLP system and data acquisition software. Prototype imaging demonstrations have shown that a 256-pixel image can be
obtained in the order of 10 seconds using compressed sensing (CS), and this speed can be improved greatly for potential
real-time or video-rate THz imaging. This photo-induced coded-aperture imaging (PI-CAI) technique has been
successfully applied to characterize THz beams in quasi-optical systems and THz horn antennas.
THz Sources I
Microdisk resonators for difference frequency generation in THz range
Show abstract
We theoretically investigated and designed a tunable, compact THz source in 1-10 THz range based on a nonlinear
optical microdisk resonator. The lack of tunable THz source operating at room temperature is still one of the major
impediments for the applications of THz radiation. The proposed device on an insulated borosilicate glass substrate
consists of a nonlinear optical disk resonator on top of another disk capable of sustaining THz modes. A pair of Si
optical waveguides is coupled to the nonlinear microdisk in order to carry the two input optical waves. Another pair of Si
THz waveguides is placed beneath the input optical waveguides to couple out the generated THz radiation from the disk
to receiver antenna. Both optical and THz disks are engineered optimally with necessary effective mode indices in order
to satisfy the phase matching condition. We present the simulation results of our proposed device using a commercial
finite element simulation tool. A distinguished THz peak coincident exactly with the theoretical calculations involving
DFG is observed in frequency spectrum of electric field in the microdisk resonator. Our device has the potential to
enable tunable, compact THz emitters and on-chip integrated spectrometers.
Dynamic lithography of v-shaped antennas for beam steering applications
Show abstract
A method to generate an optical metasurface is developed. In our experimental setup, we use a pump-probe technique,
where the pump beam is used to project patterns of v-shaped antennas on the surface of a silicon substrate. In the areas
illuminated with the images of v-shaped antennas electron-hole pairs are created. Therefore, the antenna structures on
silicon will have metallic-like properties, we classify this structure as a metasurface. The THz beam probes refraction
and reflection on the metasurface generated on the silicon substrate. The dynamic change of these patterns of
metasurface causes the beam steering effects of THz radiation.
THz Detection
Comparison of terahertz technologies for detection and identification of explosives
Show abstract
We present results on the comparison of different THz technologies for the detection and identification of a variety of
explosives from our laboratory tests that were carried out in the framework of NATO SET-193 “THz technology for
stand-off detection of explosives: from laboratory spectroscopy to detection in the field” under the same controlled
conditions. Several laser-pumped pulsed broadband THz time-domain spectroscopy (TDS) systems as well as one
electronic frequency-modulated continuous wave (FMCW) device recorded THz spectra in transmission and/or
reflection.
High-resolution terahertz atmospheric water vapor continuum measurements
Show abstract
The terahertz frequency regime is often used as the ‘chemical fingerprint’ region of the electromagnetic spectrum due to
the large number of rotational and vibrational transitions of many molecules of interest. This region of the spectrum has
particular utility for applications such as pollution monitoring and the detection of energetic chemicals using remote
sensing over long path lengths through the atmosphere. Although there has been much attention to atmospheric effects
over narrow frequency windows, accurate measurements across a wide spectrum are lacking. The water vapor continuum
absorption is an excess absorption that is unaccounted for in resonant line spectrum simulations. Currently a semiempirical
model is employed to account for this absorption, however more measurements are necessary to properly
describe the continuum absorption in this region. Fourier Transform Spectroscopy measurements from previous work are
enhanced with high-resolution broadband measurements in the atmospheric transmission window at 1.5THz. The
transmission of broadband terahertz radiation through pure water vapor as well as air with varying relative humidity
levels was recorded for multiple path lengths. The pure water vapor measurements provide accurate determination of the
line broadening parameters and experimental measurements of the transition strengths of the lines in the frequency
region. Also these measurements coupled with the atmospheric air measurements allow the water vapor continuum
absorption to be independently identified at 1.5THz. Simulations from an atmospheric absorption model using
parameters from the HITRAN database are compared with the current and previous experimental results.
THz Sources II
Characterization of graphene-based devices for THz systems
Show abstract
The H-field finite element method (FEM) based full-vector formulation is used in the present work to study the vectorial
modal field properties and the complex propagation characteristics of Surface Plasmon modes of a hollow-core dielectric
coated rectangular waveguide structures, and graphene based structures. Additionally, the finite difference time domain
(FDTD) method is used to estimate the dispersion parameters and the propagation loss of such waveguides and devices.
Multiband terahertz quasi-optical balanced hot-electron mixers based on dual-polarization sinuous antennas
Show abstract
Receivers based on superconducting Hot-Electron Bolometers (HEBs) are widely used for terahertz (THz) sensing
owing to their advantages of high sensitivity, low noise, and low LO power requirement. Balanced HEB mixers are
superior to single-element ones since the thermal noise and AM noise from the LO injection can be effectively
suppressed. Although a 1.3 THz balanced waveguide HEB mixer has been reported, waveguide mixer configurations
offer relatively narrow RF bandwidths. We report on the development, fabrication and characterization of a THz quasioptical
balanced superconducting HEB mixer utilizing a dual-polarization sinuous antenna that can potentially achieve
both multiband operation and ultra-high sensitivity. In the balanced mixer configuration, a lens-coupled four-arm
sinuous antenna was designed for operation from 0.2-1.0 THz with a nearly frequency-independent embedding
impedance of ~106 Ω. Two identical superconducting niobium HEB devices have been integrated at the antenna
feedpoints, connecting each opposing pair of antenna arms to form a balanced mixer configuration. An air-bridge was
also fabricated to separate the two mixer branches. The HEB devices were fabricated from 10 nm thick niobium film
sputtered on semi-insulating silicon substrates. Each HEB device has dimensions of 80 nm × 240 nm (3 squares) for
approaching a resistance of 105 Ω for impedance matching. Mixer properties including antenna radiation patterns,
broadband operation and polarization isolation have been characterized. Finally, in order to achieve multiband mixer
operation, electronically reconfigurable THz quasi-optical mesh filters are needed. Frequency-tunable antenna elements
using Schottky varactor diodes suitable for the above applications have been designed, simulated and demonstrated at Gband
(140-220 GHz) showing 50 GHz tuning range.
Wideband 220 GHz solid state power amplifier MMIC within minimal die size
Jerome Cheron,
Erich N. Grossman
Show abstract
A wideband and compact solid state power amplifier MMIC is simulated around 220 GHz. It utilizes 6 μm emitter length
common base HBTs from a 250 nm InP HBT technology. Specific power cells and power combiners are simulated in
order to minimize the width of the die, which must not exceed 300 μm to avoid multimode propagation in the substrate.
Four stages are implemented over a total area of the (275x1840) μm2. Simulations of this power amplifier indicate a
minimum output power of 14 dBm associated with 16 dB of power gain from 213 GHz to 240 GHz.
Novel Concepts and Applications I
Giant terahertz gain by excitation of surface plasmon polarities in optically pumped graphene
Show abstract
Interband photoexcitation in monolayer graphene can produce a weak gain in the terahertz range by only up to 2.3%, but
exciting the surface plasmon polaritons mediates the light-matter interaction, resulting in a giant terahertz gain.
Nonlinear carrier relaxation/recombination dynamics and resultant stimulated terahertz (THz) photon emission with
excitation of surface plasmon polaritons (SPPs) in photoexcited monolayer graphene has been experimentally studied
using optical-pump/THz-probe and optical-probe measurement. We observed the spatial distribution of the THz probe
pulse intensities under linear polarization of optical pump and THz probe pulses. It was clearly observed that intense
THz probe pulse was detected only at the area where the incoming THz probe pulse takes a TM mode being capable of
exciting the SPPs. The observed gain factor is in fair agreement with theoretical calculations.
Exploiting plasmonics for THz and infrared sensing
Show abstract
Bridging the gap in scale between the THz wavelength and the biomolecule sample sizes to be sensed is a challenging
task. We tackle this mismatch by developing sensing platforms based on the concepts of designer surface plasmon
polaritons and localized plasmons. We show that corrugated metallic surfaces, complementary split ring resonators and
arrays of micro-dipoles provides enhanced THz-matter interaction times and strong interrogating evanescent fields. We
will also demonstrate how transformation optics can be used to design broadband plasmonic semiconductor and metallic
gap micro-antennas for terahertz-to-visible applications.
Dispersion studies in THz plasmonic devices with cavities
Show abstract
Analytical and numerical studies of the dispersion properties of grating gated THz plasmonic structures show that
the plasmonic crystal dispersion relation can be represented in terms of effective index of the dielectric medium
around the 2DEG for the plasmons. Forbidden energy band gaps are observed at Brillion zone boundaries of the
plasmonic crystal. FDTD calculations predict the existence of the plasmonic modes with symmetrical, antisymmetrical
and asymmetrical charge distributions. Breaking the translational symmetry of the crystal lattice by
changing the electron concentration of the two dimensional electron gas (2DEG) under a single gate line in every 9th gate induces a cavity state. The induced cavity state supports a weekly-coupled cavity mode.
Coherent phenomena in terahertz 2D plasmonic structures: strong coupling, plasmonic crystals, and induced transparency by coupling of localized modes
Show abstract
The device applications of plasmonic systems such as graphene and two dimensional electron gases (2DEGs) in III-V
heterostructures include terahertz detectors, mixers, oscillators and modulators. These two dimensional (2D) plasmonic
systems are not only well-suited for device integration, but also enable the broad tunability of underdamped plasma
excitations via an applied electric field. We present demonstrations of the coherent coupling of multiple voltage tuned
GaAs/AlGaAs 2D plasmonic resonators under terahertz irradiation. By utilizing a plasmonic homodyne mixing
mechanism to downconvert the near field of plasma waves to a DC signal, we directly detect the spectrum of coupled
plasmonic micro-resonator structures at cryogenic temperatures. The 2DEG in the studied devices can be interpreted as
a plasmonic waveguide where multiple gate terminals control the 2DEG kinetic inductance. When the gate tuning of the
2DEG is spatially periodic, a one-dimensional finite plasmonic crystal forms. This results in a subwavelength structure,
much like a metamaterial element, that nonetheless Bragg scatters plasma waves from a repeated crystal unit cell. A
50% in situ tuning of the plasmonic crystal band edges is observed. By introducing gate-controlled defects or simply
terminating the lattice, localized states arise in the plasmonic crystal. Inherent asymmetries at the finite crystal
boundaries produce an induced transparency-like phenomenon due to the coupling of defect modes and crystal surface
states known as Tamm states. The demonstrated active control of coupled plasmonic resonators opens previously
unexplored avenues for sensitive direct and heterodyne THz detection, planar metamaterials, and slow-light devices.
Keynote Session
Three-dimensional invisibility cloaks functioning at terahertz frequencies
Show abstract
Quasi-three-dimensional invisibility cloaks, comprised of either homogeneous or inhomogeneous media, are
experimentally demonstrated in the terahertz regime. The inhomogeneous cloak was lithographically fabricated using
a scalable Projection Microstereolithography process. The triangular cloaking structure has a total thickness of 4.4 mm,
comprised of 220 layers of 20 μm thickness. The cloak operates at a broad frequency range between 0.3 and 0.6 THz,
and is placed over an α-lactose monohydrate absorber with rectangular shape. Characterized using angular-resolved
reflection terahertz time-domain spectroscopy, the results indicate that the terahertz invisibility cloak has successfully
concealed both the geometrical and spectroscopic signatures of the absorber, making it undetectable to the observer.
The homogeneous cloaking device made from birefringent crystalline sapphire features a large concealed volume, low
loss, and broad bandwidth. It is capable of hiding objects with a dimension nearly an order of magnitude larger than
that of its lithographic counterpart, but without involving complex and time-consuming cleanroom processing. The
cloak device was made from two 20-mm-thick high-purity sapphire prisms. The cloaking region has a maximum
height 1.75 mm with a volume of approximately 5% of the whole sample. The reflected TM beam from the cloak
shows nearly the same profile as that reflected by a flat mirror.
Novel Concepts and Applications II
T-ray detection in 0.35-um CMOS technology
Show abstract
Interest in array based imaging of terahertz energy (T-Rays) has gained traction lately, specifically using a CMOS process due to its ease of manufacturability and the use of MOSFETs as a detection mechanism. Incident terahertz radiation on to the gate channel region of a MOSFET can be related to plasmonic response waves which change the electron density and potential across the channel. The 0.35 μm silicon CMOS MOSFETs tested in this work contain varying structures, providing a range of detectors to analyze. Included are individual test transistors for which various operating parameters and modes are studied and results presented. A focus on single transistor-antenna testing provides a path for discovering the most efficient combination for coupling 0.2 THz band energy. An evaluation of fabricated terahertz band test detection MOSFETs is conducted. Sensitivity analysis and responsivity are described, in parallel with theoretical expectations of the plasmonic response in room temperature conditions. A maximum responsivity of 40 000 V/W and corresponding NEP of 10 pW/Hz1/2 (±10% uncertainty) is achieved.
THz imaging Si MOSFET system design at 215 GHz
Show abstract
Exelis Geospatial Systems and its CEIS partners at the University of Rochester and Rochester Institute of Technology
are developing an active THz imaging focal plane for use in standoff detection, molecular spectroscopy and penetration
imaging. This activity is focused on the detection of radiation centered on the atmospheric window at 215.5 GHz. The
pixel consists of a direct coupled bowtie antenna utilizing a 0.35 μm CMOS technology MOSFET, where the plasmonic
effect is the principle method of detection. With an active THz illumination source such as a Gunn diode, a design of
catadioptric optical system is presented to achieve a resolution of 3.0 mm at a standoff distance of 1.0 m. The primary
value of the initial system development is to predict the optical performance of a THz focal plane for active imaging and
to study the interaction of THz radiation with various materials.
Radar cross section measurements of frequency selective terahertz retroreflectors
Show abstract
The radar cross section of spherical retroreflectors operating at terahertz frequencies is investigated. Several spherical
retroreflectors with diameters ranging from 2 mm to 8 mm were fabricated and their radar cross section was measured at
100 GHz, 160 GHz, and 350 GHz. A frequency selective surface was applied to the retroreflectors to demonstrate proof
of concept of narrow-band terahertz retroreflection.
Poster Session
Multispectral concealed weapon detection in visible, infrared, and terahertz
Show abstract
Detection of concealed dangerous objects is a very demanding problem of public safety. So far, the problem of detecting
objects hidden under clothing was considered only in the case of airports but it is becoming more and more important for
public places like metro stations, and government buildings.
The development of imaging devices and exploration of new spectral bands is a chance to introduce new equipment for
assuring public safety. It has been proved that objects hidden under clothing can be detected and visualized using
terahertz (THz) cameras. However, passive THz cameras still offer too low image resolution for objects recognition. On
the other hand new infrared cameras offer sufficient parameters to detect objects covered with fabrics in some
conditions, as well as high image quality and big pixel resolutions.
The purpose of the studies is to investigate the possibilities of using various cameras operating in different spectral
ranges for detection of concealed objects. In the article, we present the measurement setup consisting of medium
wavelength infrared (MWIR), long wavelength infrared (LWIR), THz and visible cameras and the initial results of
measurements with various types of clothing and test objects.
Advanced designs for non-imaging submillimeter-wave Winston cone concentrators
Show abstract
We describe the design and simulation of several non-imaging concentrators designed to couple submillimeter
wavelength radiation from free space into highly overmoded, rectangular, WR-10 waveguide. Previous designs are
altered to improve the uniformity of efficiency rather than the efficiency itself. The concentrators are intended for use as
adapters between instruments using overmoded WR-10 waveguide as input or output and sources propagating through
free space. Previous simulation and measurement have shown that the angular response is primarily determined by the
Winston cone and is well predicted by geometric optics theory while the efficiencies are primarily determined by the
transition section. Additionally, previous work has shown insensitivity to polarization, orientation and beam size.
Several separate concentrator designs are studied, all of which use a Winston cone (also known as a compound parabolic
concentrator) with an input diameter ranging from 4 mm to 16 mm, and “throat” diameters of less than 0.5 mm to 4 mm
as the initial interface. The use of various length adiabatic circular-to-rectangular transition sections is investigated,
along with the effect of an additional, 25 mm waveguide section designed to model the internal waveguide of the power
meter. Adapters without a transition section and a rectangular Winston cone throat aperture and double cone
configurations are also studied. Adapters are analyzed in simulation for consistent efficiency across the opening aperture.