This PDF file contains the front matter associated with SPIE Proceedings Volume 9992 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

We have used near IR pump – Mid IR probe techniques to compare the feasibility and potential of using free standing nano-porous and micro-porous silicon (ordered hole arrays) as optically controlled modulators operating in the Mid-Wave Infrared (MWIR) covering the range from 3.3-5 μm. We employed 800 nm pumping pulses with the duration of 60 fs to reduce 4 μm light transmission modulation to about 25% and 45% for both silicon structures, respectively, at excitation powers of 50mW (4 mJ=cm²). However, at 5 μm both structures shown similar contrast of about 60%. The time resolved measurements revealed a fast sub-picosecond rise time for both structures suggesting that the optically generated carriers are a dominant mechanism for the modulation. However, the measurements demonstrated a significant difference in the relaxation dynamics. The nanoporous silicon demonstrated recovery as fast as a few tens of picoseconds and a possibility to effectively work in the GHz regime, while hole arrays shown almost three orders of magnitude slower response making it suitable for the MHz regime.

CIRTEMO, SCD and Pixelteq have co-developed a miniature short-wave infrared (SWIR) hyperspectral snapshot imager utilizing Multivariate Optical Elements (MOEs). The resultant product may address many of the detection challenges facing multiple markets including commercial, medical, security and defense. This paper highlights the design process of developing MOEs for a targeted application, as well as the technological challenges faced and solutions developed for successful integration of a micro-patterned mosaic array to an InGaAs focal plane array.

The case for new, portable, real-time mid-infrared (MIR) molecular sensing and imaging is discussed. We set a record in demonstrating extreme broad-band supercontinuum (SC) generated light 1.4-13.3 μm in a specially engineered, step-index MIR optical fiber of high numerical aperture. This was the first experimental demonstration truly to reveal the potential of MIR fibers to emit across the MIR molecular ”fingerprint spectral region” and a key first step towards bright, portable, broadband MIR sources for chemical and biomedical, molecular sensing and imaging in real-time. Potential applications are in the healthcare, security, energy, environmental monitoring, chemical-processing, manufacturing and the agriculture sectors. MIR narrow-line fiber lasers are now required to pump the fiber MIR-SC for a compact all-fiber solution. Rare-earth-ion (RE-) doped MIR fiber lasers are not yet demonstrated ≥4 μm wavelength. We have fabricated small-core RE-fiber with photoluminescence across 3.5-6 μm, and long excited-state lifetimes. MIR-RE-fiber lasers are also applicable as discrete MIR fiber sensors in their own right, for applications including: ship-to-ship free-space communications, aircraft counter-measures, coherent MIR imaging, MIR-optical coherent tomography, laser-cutting/ patterning of soft materials and new wavelengths for fiber laser medical surgery.

We report on recent progress in developing an industrially relevant, robust technique to bond dissimilar materials through ultra-fast microwelding. This technique is based on the use of a 5.9ps, 400kHz Trumpf laser operating at 1030nm. Tight focusing of the laser radiation at, or around, the interface between two materials allows for simultaneous absorption in both. This absorption rapidly, and locally, heats the material forming plasma from both materials. With suitable surface preparation this plasma can be confined to the interface region where it mixes, cools and forms a weld between the two materials.

The use of ps pulses results in a short interaction time. This enables a bond to form whilst limiting the heat affected zone (HAZ) to a region of only a few hundred micrometres across. This small scale allows for the bonding of materials with highly dissimilar thermal properties, and in particular coefficients of thermal expansion e.g. glass-metal bonding.

We report on our results for a range of material combinations including, Al-Bk7, Al-SiO2 and Nd:YAG-AlSi. Emphasis will be laid on the technical requirements for bonding including the required surface preparation of the two materials and on the laser parameters required. The quality of the resultant bonds are characterized through shear force measurements (where strengths equal to and exceeding equivalent adhesives will be presented). The lifetime of the welds is also discussed, paying particular attention to the results of thermal cycling tests.

Hyperspectral imaging from unmanned aerial vehicles arouses a growing interest, as well for agriculture management as pollution monitoring or security purposes. Most of current instruments are in the visible or near infrared spectral range, but the midwave or longwave infrared may also be interesting. Among the available solutions for compact imaging spectrometers in this spectral range, static imaging Fourier transform spectrometers are well adapted, thanks to the absence of moving part, a 2D snapshot imaging, which can be useful for image registration, and a high flux collection efficiency. To reach a high compactness compliant with small UAVs, birefringent interferometers are good candidates. Indeed, they can be roughly seen as a plate which comes in front of the camera lens. We propose here firstly to expose the design rules of such instruments in the midwave or longwave infrared. The first point is about the material: highly birefringent uniaxial crystals materials are not so common in this spectral domain. For MWIR spectral imagers, TeO2 or YVO4 can be used. For LWIR instruments, current materials, like ZnGeP2 or AgGaS2 are available, but their birefringence is not so high. Calomel is a promising way, but not still available. The second point consists in defining the type of interferometer, like Savart interferometer, Wollaston interferometer, or other designs. To help this choice, we have developed a software tool to calculate the propagation of plane waves in a stack of birefringent plates. This allows us to choose the optimal assembly of the plates to reach the required spectral resolution. We will then present experimental results obtained with a MWIR prototype. This prototype, called SIBI,, works in the [3.7µm-4.8µm] spectral domain (or [2050cm 1-2700cm 1]), with a spectral resolution about 13cm 1. A first ground campaign was led in June 2015, on Mount Etna (Italy). This campaign was useful to emphasize the assets and drawbacks of this instrument. Among the assets, we can quote the easiness to deploy this instrument, especially thanks to its small size, its light weight and its sturdiness. Among the difficulties that we have to face with, we can quote the presence of ghost fringes, which debased the final quality of the spectra. However solutions are available to prevent this difficulty. Finally, we will present the adaptation of SIBI to airborne campaigns, aboard a small UAV. This campaign is expected for August, 2016.

Ultrafast electron spectroscopy – the use of sub-ns pulses of electrons to excite materials of interest – offers many opportunities in the study of novel ultra-violet emitters and detectors. Due to the variability of electron energy one may go from tens of electronvolts to tens of Kiloelectronvolts; from probing the dynamics of conduction-band states to penetrating bulk samples in the interest of interacting with unoccupied states and measuring lattice scattering, tasks that traditional photon-based ultrafast spectroscopy is simply unable to perform. Furthermore, the added capability of time-correlated measurement allows for these properties to be studied in an unprecedented way. Presented is a photo-excited electron gun system capable of sub-ns pulses used to probe phosphors for betaphotovoltaics and the carrier dynamics of Nitride heterostructures grown for the purpose of UV detection and emission. The electron gun, itself, is a Kimball-built system capable of electron acceleration up to, and including, 30keV. Frequency-doubled light from a 250-kHz Coherent Ti:sapphire laser system is focussed on a LaB6 cathode, capable of either thermionic emission or photoemission. The electron gun allows for the exchange of photocathodes to test novel emitters in the interests of further advancing and refining the electron gun system’s capabilities. Emitted electrons are then focussed and diverted using magnetic optics and onto the sample. Light emission from the sample is collected and directed out of the vacuum chambre and into a PMT-enabled monochromator. The use of a PMT allows for single-photon counting and accurate time-correlated measurement. The phosphors studied were LaPO4:Pr and ZnS, photon emitters to be paired with InGaN and InGaP, respectively, for the purposes of betaphotovoltaic power generation – a long-lived power source. The use of the 30keV-capable electron gun is ideal for these purposes as it is able to measure the phosphor’s beta response over a broad energy spectrum, covering the entire spectrum of tritium and most of that of 63Ni, our two candidates for beta sources. The combination of a UV source and detector bearing the same efficiency as the visible source would allow for betaphotovoltaic generators with greater tension for more varied applications. Research has also been performed on InGaN/GaN structures for solar-blind UV detection and emission. Moving into the UV region has introduced challenges for which electron sources are perfectly suited; from the difficulty of p-type growth at these energy levels to the need to study carrier dynamics in novel materials. None of this is to say that the generation of these bunches of electrons is a trivial matter: that electrons are charged introduces temporal and spatial broadening that is difficult to overcome, the collection of emitted signals introduces complications, and the measurement of pulses of electrons shorter than 1ns is difficult with the current state of detector technology, but these problems provide the opportunity for new solutions, as well.

The parameters of whispering gallery modes resonators can be significantly modified under the action of external factors, for instance, in the case of resonator movement. The effects, which take place in the moving resonators of whispering gallery modes, can be employed for measuring of the angular velocity. In this work we was compared the influence of centrifugal forces and the Sagnac effect on the eigenfrequencies (wavelengths) of whispering gallery modes resonators. Also work is devoted mutual relationships of the effects.

The XCAN project, which is a three years project and began in 2015, carried out by Thales and the Ecole Polytechnique aims at developing a laser system based on the coherent combination of laser beams produced through a network of amplifying optical fibers. This technique provides an attractive mean of reaching simultaneously the high peak and high average powers required for various industrial, scientific and defense applications. The architecture has to be compatible with very large number of fibers (1000-10000). The goal of XCAN is to overcome all the key scientific and technological barriers to the design and development of an experimental laser demonstrator. The coherent addition of multiple individual phased beams is aimed to provide tens of Gigawatt peak power at 50 kHz repetition rate. Coherent beam combining (CBC) of fiber amplifiers involves a master oscillator which is split into N fiber channels and then amplified through series of polarization maintaining fiber pre-amplifiers and amplifiers. In the so-called tiled aperture configuration, the N fibers are arranged in an array and collimated in the near field of the laser output. The N beamlets then interfere constructively in the far field, and give a bright central lobe. CBC techniques with active phase locking involve phase mismatch detection, calculation of the correction and phase compensation of each amplifier by means of phase modulators. Interferometric phase measurement has proven to be particularly well suited to phase-lock a very large number of fibers in continuous regime. A small fraction of the N beamlets is imaged onto a camera. The beamlets interfere separately with a reference beam. The phase mismatch of each beam is then calculated from the interferences’ position. In this presentation, we demonstrate the phase locking of 19 fibers in femtosecond pulse regime with this technique. In our first experiment, a master oscillator generates pulses of 300 fs (chirped at 200 ps). The beam is split into 19 passive channels. Prior to phase locking, the optical path differences are adjusted down to 10 μm with optical delay lines. Interferograms of the 19 fibers are recorded at 1 kHz with a camera. A dedicated algorithm is developed to measure both the phase and the delay between the fibers on a measurement path. The delay and phase shift are thus calculated collectively from a single image and piezo-electric fiber stretchers are controlled in order to ensure compensation of time-varying phase and delay variations. The residual phase shift error is below λ/60 rms. The coherent beam combining is obtained after propagation and compression. The combined pulse width is measured at 315fs. A second experiment was done to coherently combine two amplified channels of the XCAN demonstrator. A residual phase shift error of λ/30 rms was measured in this case.

Laser diodes fabricated from the AlGaInN material system is an emerging technology for defence, security and sensing applications. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the visible ~530nm, by tuning the indium content of the laser GaInN quantum well, giving rise to new and novel applications including displays and imaging systems, free-space and underwater telecommunications and the latest quantum technologies such as optical atomic clocks and atom interferometry.

Lasers developed for defence related applications typically encounter issues with reliability and meeting desired specification when taken from the lab to the product line. In particular the harsh environmental conditions a laser has to endure can lead to difficulties. This paper examines a specific class of laser, namely actively mode-locked fibre lasers (AMLFLs), and discusses the impact of environmental perturbations. Theoretical and experimental results have assisted in developing techniques to improve the stability of a mode-locked pulse train for continuous operation. Many of the lessons learned in this research are applicable to a much broader category of lasers.

The AMLFL consists of a fibre ring cavity containing a semiconductor optical amplifier (SOA), an isolator, an output coupler, a circulator, a bandpass filter and a modulator. The laser produces a train of 6-ps pulses at 800 nm with a repetition rate in the GHz regime and a low-noise profile. This performance is realisable in a laboratory environment. However, even small changes in temperature on the order of 0.1 °C can cause a collapse of mode-locked dynamics such that the required stability cannot be achieved without suitable feedback. Investigations into the root causes of this failure were performed by changing the temperature of components that constitute the laser resonator and observing their properties.

Several different feedback mechanisms have been investigated to improve laser stability in an environment with dynamic temperature changes. Active cavity length control will be discussed along with DC bias control of the Mach-Zehnder modulator (MZM).

Point-like sources of X-rays that are pulsed (sub nanosecond), high energy (up to several MeV) and bright are very promising for industrial and security applications where imaging through large and dense objects is required. Highly penetrating X-rays can be produced by electrons that have been accelerated by a high intensity laser pulse incident onto a thin solid target. We have used a pulse length of ~10ps to accelerate electrons to create a bright x-ray source. The bremsstrahlung temperature was measured for a laser intensity from 8.5-12×10¹⁸ W/cm². These x-rays have sequentially been used to image high density materials using image plate and a pixelated scintillator system.

We propose deterministic sampling strategies for compressive imaging based on Delsarte-Goethals frames. We show that these sampling strategies result in multi-scale measurements which can be related to the 2D Haar wavelet transform. We demonstrate the effectiveness of our proposed strategies through numerical experiments.

Novel types of spectral sensors using coded apertures may offer various advantages over conventional designs, especially the possibility of compressive measurements that could exceed the expected spatial, temporal or spectral resolution of the system. However, the nature of the measurement process imposes certain limitations, especially on the noise performance of the sensor. This paper considers a particular type of coded-aperture spectral imager and uses analytical and numerical modelling to compare its expected noise performance with conventional hyperspectral sensors. It is shown that conventional sensors may have an advantage in conditions where signal levels are high, such as bright light or slow scanning, but that coded-aperture sensors may be advantageous in low-signal conditions.

We introduce a system that exploits 3-D imaging technology as an enabler for the robust recognition of the human form. We combine this with pose and feature recognition capabilities from which we can recognise high-level human behaviours. We propose a hierarchical methodology for the recognition of complex human behaviours, based on the identification of a set of atomic behaviours, individual and sequential poses (e.g. standing, sitting, walking, drinking and eating) that provides a framework from which we adopt time-based machine learning techniques to recognise complex behaviour patterns.

We propose and demonstrate an coherent imaging technique by using defocus grating. For the imaging system, the defocus grating combined with lens with short focal length is used to realize multiplane imaging on the lens' focal plane, simultaneously. Based on these multiplane images, Gerchberg-Saxton (GS) algorithm is used to reconstruct the complex amplitude distribution of the input imaging beam. By using computational imaging and digital wavefront distortion correction with stochastic parallel gradient descent (SPGD) algorithm, this technology can be used for joint estimation of both pupil aberrations and an high resolution image of the object, successfully.

A new generation of quantum technology based systems, exploiting effects such as superposition and entanglement, will enable widespread, highly disruptive applications which are expected to be of great economic significance. However, the technology is only just emerging from the physics laboratory and generally remains at low TRLs. The question is: where, and when, will this impact be first manifest? The UK, with substantial Government backing, has embarked on an ambitious national program to accelerate the process of technology transfer with the objective of seizing a significant and sustainable share of the future economic benefit for the UK. Many challenges and uncertainties remain but the combined and co-ordinated efforts of Government, Industry and Academia are making great progress. The level of collaboration is unusually high and the goal of embedding a “QT Ecosystem” in the UK looks to be attainable. This paper describes the UK national programme, its key players, and their respective roles. It will illustrate some of the likely first commercial applications and provide a status update. Some of the challenges that might prevent realisation of the goal will be highlighted.

Recent advances in the field of quantum technology offer the exciting possibility of gravimeters and gravity gradiometers capable of performing rapid surveys with unprecedented precision and accuracy. Measurements with sub nano-g (a billionth of the acceleration due to gravity) precision should enable the resolution of underground structures on metre length scales. However, deducing the exact dimensions of the structure producing the measured gravity anomaly is known to be an ill-posed inversion problem. Furthermore, the measurement process will be affected by multiple sources of uncertainty that increase the range of plausible solutions that fit the measured data. Bayesian inference is the natural framework for accommodating these uncertainties and providing a fully probabilistic assessment of possible structures producing inhomogeneities in the gravitational field. Previous work introduced the probability of excavation map as a means to convert the high-dimensional space belonging to the posterior distribution to an easily interpretable map. We now report on the development of the inference model to account for spatial correlations in the gravitational field induced by variations in soil density.

The recent development of 2D arrays of single-photon avalanche diodes (SPAD) has driven the development of applications based on the ability to capture light in motion. Such arrays are composed typically of 32x32 SPAD detectors, each having the ability to detect single photons and measure their time of arrival with a resolution of about 100 ps. Thanks to the single-photon sensitivity and the high temporal resolution of these detectors, it is now possible to image light as it is travelling on a centimetre scale. This opens the door for the direct observation and study of dynamics evolving over picoseconds and nanoseconds timescales such as laser propagation in air, laser-induced plasma and laser propagation in optical fibres. Another interesting application enabled by the ability to image light in motion is the detection of objects hidden from view, based on the recording of scattered waves originating from objects hidden by an obstacle. Similarly to LIDAR systems, the temporal information acquired at every pixel of a SPAD array, combined with the spatial information it provides, allows to pinpoint the position of an object located outside the line-of-sight of the detector. A non-line-of-sight tracking can be a valuable asset in many scenarios, including for search and rescue mission and safer autonomous driving.

Single-photon avalanche diodes (SPADs) in the form of high-resolution imaging pixel arrays are used in 3D cameras, motion-tracking, biomedical and time-correlated single photon counting (TCSPC) applications. Rapid spatial and temporal zoom onto objects of interest is an attractive feature. We present here novel high-speed time-zoom functionality achieved with the digital readout mode of the TACImager, a 256 x 256 TCSPC image sensor array based on sample and hold Time to Amplitude Converter (TAC) pixels. A column-parallel flash Analogue to Digital Converter (ADC) is implemented in the TACImager to support fast digital readout, allowing per-pixel, 3-bin TCSPC histogramming at frame rates of 4 kfps. New results related to this high-speed mode of operation are presented. The TACImager utilises a global ramp voltage as a timing reference, allowing time-zoom to be achieved through dynamic adjustment of comparator voltages, ramp offset voltages and ramp waveforms. We demonstrate the influence of fixed pattern noise in the pixels and column parallel ADCs on the results.

Advances in LIDAR-based methods have enabled the detection and reconstruction of images of static objects hidden from the direct line-of-sight [1, 2]. One of the drawbacks to the technology used in these demonstrations is the requirement for long acquisition times. More recently, Gariepy et al. have shown that it is possible to detect and track a moving hidden object, albeit with no information of the object’s form [3]. Applications of this include, but are not limited to, search and rescue, and hazard detection. We present a real-time tracking system that enables the detection of moving objects that are outside the direct line-of-sight. Our active imaging system is a single-pixel variant of the technology reported by Gariepy et al. It replaces the single-photon avalanche diode (SPAD) camera of 1024 pixels with a number of SPAD detectors to detect light back-scattered from the hidden object. The flexibility of the single-pixel detectors provides an increased field of view, allowing us to detect and simultaneously track with better precision with respect to a SPAD array. The use of single-pixel detectors also has the advantage of a high detection efficiency. We perform two proof-of-concept experiments using three pixels and a single pulsed laser to interrogate a “room” for a hidden object. In the first experiment, we demonstrate that we can accurately locate the position of a hidden object. In the second experiment, we use the same system and demonstrate that we can accurately track the motion of a hidden object in real time. The “room” is a purpose-built box measuring 102×102×77 cm. Optical access is provided by a 28×12 cm window. The target object is a 15×15 cm textured viewing screen that we move along a designated ground track outside the line-of- sight of our system. In our experiments, we send a train of light pulses through the window to the back of the room. The pulses scatter off the wall as a spherical wavefront that propagates in all directions. Some of this light reaches our hidden object and is scattered back again towards the rear wall where we image our three SPAD pixels. The SPAD detectors are capable of picosecond temporal resolutions. Our time-correlated single-photon counting system measures the photon arrival times (64 ps resolution) for the signal returning to each detector. A histogram is built up in one second of acquisition time over 80 million pulses. We use this temporal information in our target position retrieval of the hidden object. We place the object at 11 positions in turn in a seven minute experiment, and localise its position. We then perform real-time tracking and move the object around the hidden scene for approximately one minute, processing the target position retrieval every 1.5 s.

This paper presents an optical depth imaging system optimized for highly scattering environments such as underwater. The system is based on the time-correlated single-photon counting (TCSPC) technique and the time-of-flight approach. Laboratory-based measurements demonstrate the potential of underwater depth imaging, with specific attention given to environments with a high level of scattering.

The optical system comprised a monostatic transceiver unit, a fiber-coupled supercontinuum laser source with a wavelength tunable acousto-optic filter (AOTF), and a fiber-coupled single-element silicon single-photon avalanche diode (SPAD) detector. In the optical system, the transmit and receive channels in the transceiver unit were overlapped in a coaxial optical configuration. The targets were placed in a 1.75 meter long tank, and raster scanned using two galvo-mirrors. Laboratory-based experiments demonstrate depth profiling performed with up to nine attenuation lengths between the transceiver and target. All of the measurements were taken with an average laser power of less than 1mW.

Initially, the data was processed using a straightforward pixel-wise cross-correlation of the return timing signal with the system instrumental timing response. More advanced algorithms were then used to process these cross-correlation results. These results illustrate the potential for the reconstruction of images in highly scattering environments, and to permit the investigation of much shorter acquisition time scans. These algorithms take advantage of the data sparseness under the Discrete Cosine Transform (DCT) and the correlation between adjacent pixels, to restore the depth and reflectivity images.

Influence of the centrifugal forces on angular velocity sensors that measure a spectral shift of whispering gallery modes is investigated. Spherical whispering gallery mode resonators of different materials are considered as sensing elements. The study is based on the results of the simulation in OOFELIEMultiphysics software.