This PDF file contains the front matter associated with SPIE Proceedings Volume 10656, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

The main goal of this study was to investigate the potential of hyperspectral imaging as a non-destructive rapid quality control method for grading cured tobacco bales. Cultivated tobacco plants are harvested and cured before using in the manufacture of tobacco products. Cured tobacco leaf bales are then graded by humans based on visual, physical and sensory characteristics. Hyperspectral imaging can be used as a tool to streamline the tobacco grading process and assist the human graders. Hyperspectral images of cured tobacco bales were acquired using a visible near-infrared (VNIR) hyperspectral pushbroom imaging system (400-1000 nm). Multivariate calibration models were built using end-member extraction and linear discriminant analysis (LDA). The LDA model using Mahalanobis distance metric showed clear discrimination between the different tobacco grades. The relative classification accuracy of this method for Flue Cured and Burley tobacco grades were 93%. This study demonstrates that hyperspectral imaging can be used as a reliable, rapid, non-destructive quality control method for grading cured tobacco bales.

Industrial Relevance: This hyperspectral grading system has been developed for tobacco, but can be potentially practiced with other agricultural products such as tea, coffee, grapes etc.

Strobed LED spectral imaging systems share some principles with illumination filter wheel systems. The major advantages of strobed LED systems are: 1) speed, 2) no mechanical movement, 3) no dependency on unstable broadspectrum incandescent light source, 4) potential for high dynamic range imaging through the illumination, and 5) combined spectral reflectance imaging and spectral fluorescence imaging. All of the above advantages are exploited in the proposed system where the spectral illumination source is combined with an integrating sphere and a calibration model that provides traceability, high reproducibility, spatial homogeneity, and focus on chemical properties of a heterogenous sample. Application areas of such systems are quite broad and high performance systems are seen within fields like agriculture, food, pharmaceuticals, medical devices, cosmetics, forensics, cultural heritage, and general manufacturing. We will present the elements of our strobed LED imaging systems and highlight how such systems can be advantageous to other spectral imaging techniques like pushbroom imaging. The powerful multivariate analysis technique, normalized canonical discriminant analysis (nCDA) is used to optimize the application performance as well as to get information about the data/noise structure and importance of specific spectral ranges. The performance is illustrated on a number of real applications from industries within the above mentioned fields. Applications on agricultural seed analysis, coating analysis, food contamination, and counterfeit detection will be shown.

Hyperspectral and multispectral imagers have been developed and deployed on satellite and manned aerial platforms for decades and have been used to produce spectrally resolved reflectance and other radiometric products. Similarly, light detection and ranging, or LIDAR, systems are regularly deployed from manned aerial platforms to produce a variety of products, including digital elevation models. While both types of systems have demonstrated impressive capabilities from these conventional platforms, for some applications it is desirable to have higher spatial resolution and more deployment flexibility than satellite or manned aerial platforms can offer. Commercially available unmanned aerial systems, or UAS, have recently emerged as an alternative platform for deploying optical imaging and detection systems, including spectral imagers and high resolution cameras. By enabling deployments in rugged terrain, collections at low altitudes, and flight durations of several hours, UAS offer the opportunity to obtain high spatial resolution products over multiple square kilometers in remote locations. Taking advantage of this emerging capability, our team recently deployed a commercial UAS to collect hyperspectral imagery, RGB imagery, and photogrammetry products at a legacy underground nuclear explosion test site and its surrounds. Ground based point spectrometer data collected over the same area serves as ground truth for the airborne results. The collected data is being used to map the site and evaluate the utility of optical remote sensing techniques for measuring signatures of interest, such as the mineralogy, anthropogenic objects, and vegetative health. This work will overview our test campaign, our results to date, and our plans for future work.

The use of machine learning algorithms is used extensively when analyzing and labeling image data. However, these techniques also offer additional post-processing advantages when they are used to calibrate sensor data. In this paper, a new calibration strategy for a Snapshot Hyperspectral Imaging Fourier Transform (SHIFT) spectrometer is discussed. The method, which is based on use of artificial neural networks, offers greater accuracy in both space and frequency when compared to conventional post-processing techniques. A theoretical model for the calibration procedure is presented, the laboratory data collection protocol is provided, and validation is conducted by measuring NIST-traceable spectral reflectance standards.

Itch is the primary symptom of inflammatory skin diseases such as atopic eczema and psoriasis, chronic renal failure, and chronic hepatic failure. Itch, like pain, is a subjective symptom. Characterizing itchy skin and skin prone to itch will lead to better understanding of these symptoms and ultimately better diagnosis and treatment of the underlining disease. The goal of our study is to determine whether the itchy skin region can be detected by hyperspectral imaging. We used an imaging system equipped with liquid crystal tunable filter for collecting hyperspectral images. A halogen lamp was used to illuminate the region of interest. Images were taken from 650 nm to 1100 nm wavelength with 10 nm interval. The hyperspectral images were collected from the forearms of two male and two female subjects. An approximate 50 mm × 50 mm region of interest was marked on the forearms before imaging. The itch was mechanically induced. Imaging was performed for three conditions with a 99% Spectralon white diffuse reflectance target on the side: before inducing itch (normal region), after inducing itch (test region), and after removing itch (control region). Two methods were used to detect the itchy and nonitchy regions from the normalized hyperspectral data. The first method used a spectral distribution exploration method. The second method used a supervised classification method, more specifically, a support vector machine (SVM) algorithm. The spectral distribution exploration method did not detect any different spectral signature for itchy region. On the other hand, the SVM classifier detected the itchy region with the surrounding non-itchy region. These results demonstrated the feasibility of using hyperspectral imaging combined with classification algorithms for detecting itchy skin region.

The mid- and far infrared are tantalizing regions of the electromagnetic spectrum, containing great information about thermal and chemical properties of objects and materials; however, semiconductor materials that interact with light in this range are often extremely difficult to use, especially at room temperature. Thermal detectors in the form of microbolometers have had great commercial success in the uncooled camera market, but they have significant limitations when speed or spectral selectivity is needed. This presentation reviews the basic properties and performance of microbolometers and other uncooled thermal detectors. The basic physical limits of thermal detector performance are discussed; these include noise sources, temperature stability, ultimate speeds, ultimate sensitivities, quantum noise effects at far-IR and THz wavelengths, and thermomechanical limits on spectral resolution. With this background, we will explore how the radiation noise limit differs between traditional microbolometers with wide absorption and detectors with narrower spectral pass bands. This can allow improved performance because narrowband microbolometers and thermal detectors can theoretically operate near the performance of cooled detectors. The presentation will discuss some preliminary work at Minnesota showing the highest D* uncooled detectors reported to date as a milestone in our attempt to approach the background limit. The presentation will conclude with some speculations on how research on uncooled detectors will progress in the next 10 years. These speculations will include aspects of pixel design, new materials for optical performance and electrical readout, design for high temperature operation, and other detector characteristics.

We explored the effect of Cr dopant on the transport behaviors of polycrystalline VO2 thin films in order to suppress the sharp metal-insulator transition, and tune the temperature coefficient of resistivity (TCR) value. A reactive bias target ion beam deposition was used for combinational sputtering to Cr doped VO2 thin films (~100 nm). The addition of Cr led a structural change in the semiconducting phase of VO2. With the Cr content >7 at. %, the sharp metal-semiconductor transition and the hysteresis loop was suppressed in thin film VO2. A further increase of Cr content reduced the TCR. Separately the effect of the oxygen flow rate was investigated to modulate the TCR and the resistivity value of Cr doped VO2. We demonstrated the resistivity of Cr doped VO2 was modulated by 2 orders of magnitude with a very small change in the oxygen flow rate. We obtained TCR of ~ 4.5 %/K in Cr doped VO2 grown on single crystal sapphire substrate near room temperature.

This paper highlights our recent work on wavelength-selective air-bridge infrared bolometers for the 8-12 and 3-5 micron wavelength bands. Gold-black coatings specially protected to enable patterned deposition on bolometer arrays have provided enhanced dual band sensitivity. Subwavelength metal-insulator-metal (MIM) resonant structures were patterned on individual air-bridge bolometers to provide design-tunable enhancement of absorption, which can be engineered to span the 8-12 micron band, or to select narrowly within each considered band for infrared spectral sensing. The choice of MIM dielectric depends critically on refractive-index dispersion at the wavelengths of interest. Integrating the bolometric material within the MIM absorber, and minimizing layer thicknesses, can optimize detector speeds. Deposition of nanocrystalline VO_x and TiO₂ by aqueous-spray heterogeneous chemical reaction is investigated as a means of producing bolometric thin films and MIM dielectrics, respectively.

Electrical conduction in materials used in microbolometer technology, such as vanadium oxide (VOx) and amorphous silicon (a-Si), is via carrier hopping between localized states. The hopping conduction parameters determine the temperature coefficient of resistance (TCR), its temperature dependence, and its relationship to resistivity. The electrical noise has a 1/f component that is also associated to the hopping parameters and thus correlated to TCR. Current research on conduction in cross linked metal nanoparticles organized in an insulating matrix shows that TCR and noise can be controlled independently, potentially allowing for precise tailoring of the detector response for differing applications.

A set of experiments were conducted looking at how characteristics of loop elements in an array affect their detected induced current and subsequent Joule heating when located in a radio frequency magnetic field. These experiments included evaluations of the observed steady state temperature rise versus the radius of the loop, the location of the loop with respect to the RF source, and the effect on steady state temperature rise when other loops were brought into close proximity. Loop elements were then combined into a radially-symmetric, five-element array which was used to create a coarse magnetic image of a simple piece of aluminum sheet. After normalization, the temperature rise versus loop size results showed a direct linear relationship which enabled prediction of the lower element size threshold based on the properties of existing thermosensing layer materials used in other bolometer applications and the typical performance of analog measurement equipment. Offset sample test results show how the RF field varied linearly across a given plane perpendicular to the RF source transmission axis, increasing as the distance between the sample and one side of the Helmholtz coil is reduced. Separation distance test results also reveal the RF magnetic field cancellation effects due to mutual coupling as the separation between closed-loop elements are brought into close proximity. Lastly, the excellent agreement achieved between the captured image and the actual object show promise in creating an imaging system with significant resolution and contrast differentiation.

We have investigated microwave power detection based from carbon nanotube (CNT) thin films and chemical vapor deposition (CVD) grown graphene. Our experiments indicate that power detection from the CNT devices is primarily due to bolometric mechanisms. While, power detection from the graphene devices is primarily due to signal rectification. Both enabling materials are relatively inexpensive and easily blanketed on a variety of substrates{enabling low-cost/disposable, surface-conformal power sensors for wideband spectrum sensing applications. However, it is significantly less challenging to pattern and integrate CNT thin films than it is to do the same with graphene. CNT thin film and graphene power detectors were realized by fabricating metallic Corbino disc test structures over these enabling materials. Such test structures are convenient for on-wafer characterization with ground-signal probes. The CNT devices were also evaluated with transient current-versus- voltage traces and microwave reflection spectroscopy to respectively measure thermal time constants and values of complex conductivity. The bolometer performance of these devices was gauged in terms of power detection sensitivity, noise equivalent power, and dynamic range. The measurements were performed with 915 MHz test signals and yielded sensitivities as high as 0.36 mV/mW at room temperature and 2.3 mV/mW when cooled with liquid nitrogen. Similarly, graphene Corbino disc test structures were characterized with 433.92 MHz test signals and yielded power detection sensitivities of 3.25 mV/mW (at room temperature) and 5.43 mV/mW (at 80 K). These devices feature gate control over the channel conductance, which contributed a frequency-limiting parasitic capacitance. Our investigations revealed that rectification, due to characteristic nonlinear current versus voltage behavior, was more prevalent in the graphene than bolometric detection, due to Joule heating.

This paper reviews recent developments in customized packaged bolometers at INO with an emphasis on their applications. The evolution of INOs bolometer packages is also presented. Fully packaged focal plane arrays of broadband microbolometers with expanded absorbing range are shown, for applications in spectroscopic and THz imaging. This paper also reports on the development of customized packaged bolometer focal plane arrays (FPAs) for space applications such as a multispectral imaging radiometer for fire diagnosis, a far infrared radiometer for in-situ measurements of ice clouds and a net flux radiometer for Mars exploration.

Avalanche photodiodes (APDs) can provide higher sensitivity than p-i-n photodiodes owing to their internal gain. However, the gain, which originates from impact ionization is also a source of noise. Recently, using Al_xIn_1-xAs_ySb_1-y grown as a digital alloy we have demonstrated APDs with noise as low as Si at telecommunication wavelengths (1300 nm to 1550 nm). In this paper, we report on additional AlInGaAsSb digital alloys and demonstrate noise suppression relative to random alloys. This is related to the fundamental issue of transport in ordered materials and provides the potential for “designer APDs” covering a broad range of spectral bands.

Xenics developed a family of stitched 12.5 μm pitch SWIR line-arrays achieving line rates up to 400 KHz, based on a modular ROIC design with modules of 512 pixels, stitched during fabrication into 512, 1024 and 2048 pixel arrays, enabling longer arrays to run at a high line rate irrespective of the array length. The front-end circuit is based on a CTIA ensuring stable detector bias, good linearity and signal integrity, input auto-zero allowing low detector bias, and CDS reducing noise and offsets. The FPA has a pixel pitch of 12.5μm and has two pixel flavors: square (12.5x12.5 μm) and rectangular (12.5x250 μm). The ROIC is flip-chipped with InGaAs detector arrays, ensuring low parasitic capacitance and consequently low noise. Five gain modes have been implemented with input referred noise of 35e_rms in the highest gain mode. The FPA operates in Integrate While Read mode and, at a master clock rate of 60 MHz and a minimum integration time of 1.4 μs, achieves the highest line rate of 400 KHz.

In this paper, design details and measurements results are presented in order to demonstrate the array performance.

In this paper, we present the test results of a flight-grade 13μm pixel pitch 6000-element 1.7μm InGaAs linear array in a hermetic package, designed and developed for space remote sensing and imaging applications. The array consists of a single 13μm pixel pitch 6000-element InGaAs linear array and a custom single digital 2.0 Mecapacitance trans-impedance amplifier (CTIA) readout integrated circuit (ROIC) with four gains. We have achieved greater than 80% peak quantum efficiency and higher than 1100 signal-to-noise ratio (SNR) at 90% well fill. The focal plane array is in a vacuum hermatically sealed package with an anti-reflective (AR)-coated Sapphire window and 29 pins, including four for low voltage differential signaling (LVDS) outputs.

SWIR (Short Wave Infrared) imaging can be of great use in precision agriculture, food processing and recycling industry, among other fields. However, hyperspectral SWIR cameras are costly and bulky, preventing their widespread deployment on the field. To answer the market need for compact and cost-efficient hyperspectral cameras covering the SWIR range, imec and SCD have joined efforts to develop a novel integration approach combining imec know-how in pixel level patterned thin film spectral filter technology, with SCD’s InGaAs technology. The here presented line-scan SWIR hyperspectral camera covers the 1.1-1.65 μm range with 100+ bands and a spectral resolution better than 10 nm. This imager uses a set of patterned Fabry-Pérot interferometers processed using semiconductor grade thin-film technology. The optical filters are then integrated directly on top of the sensing side of the InGaAs detector with high accuracy and with a minimum gap between filters and Focal Plane Array to limit cross-talk. The resulting line-scan camera, measuring only 70x62x60 mm and with a weight below 0.5kg, is the lightest and most compact SWIR hyperspectral camera on the market. Full sensor readout can be performed at up to 350 fps. An imecpatented SnapScan system with internal scanning was also developed, capable of acquiring data cubes of 640x512x128 pixels in a second. Maximum cube size is 1200x640x128. By selecting a subset of contiguous spectral bands and a reduced spatial resolution the sensor could be operated @ +1000 fps, for example enabling cube acquisitions of 320x512x64 in less than 300 ms.

HgCdTe films are grown by molecular beam epitaxy (MBE) on large area CdZnTe substrates to achieve low dark current, high quantum efficiency infrared image sensors with 1.7um and 2.5um cut-off respectively. We present the structural and optical characterization of our HgCdTe films with emphasis on spatial uniformity across 7x7.5cm2 wafer size. Science grade detectors are fabricated on these films and subsequently hybridized to our H4RG-15 4K x 4K readout integrated circuit (ROIC). Test results from these image sensors show low dark current (<0.01e-/pixel/sec), high quantum efficiency across the target spectral range (70-90%), <20e single CDS noise, high operability (>99%), less than 1.0% cross talk and a well capacity larger than 70,000e-. the operation temperature is between 80-110K. These image sensors are also responsive in the visible-IR region due removal of the CdZnTe substrate after hybridization. This feature enables spectrographs to use a single image sensor for both visible and IR regions. These image sensors are developed for extremely large telescopes and used in various telescopes around the world.

A novel broadband photodetector and its array having spectral response ranging from visible to shortwave infrared (VIS-SWIR) is developed for focal plane array (FPA) for military, security, industrial imaging applications, and optical communications. The photodetector is based on InGaAs and fabricated on InP substrate, exhibiting high sensitivity, high quantum efficiency, and yet cost-effective. In order to realize a small weight, power, and cost effectiveness (SWAP-C) camera and receiver, the photodetector requires having low dark current at high operating temperatures, which saves power for cooling. This paper explains the photodetector structure, design-simulation for optimizing the structural parameters, and performance of the photodetector. An analytical closed form model is derived for design and simulation of the broadband photodetector. Both theoretical and experimental results of electrical and optical characteristics of the photodetectors are also presented in this paper.

Computational imaging relies on the joint design of optics and digital processing for producing the final digital image our output. Because the intermediate optical image need preserve the relevant visual information yet not necessarily "look good," a wider range of optical designs can be employed, including designs that eschew traditional optical elements such as lenses and curved mirrors. There are three primary approaches to such lensless imaging, based on 1) diffraction by special optical gratings, 2) in-line digital holography and computational phase recovery, and 3) compressive sensing using sets of pseudo-random masks. Each technique has relative strengths and weaknesses in computational burden, image accuracy, and are appropriate for different target applications.

Lower-dimensional photopolymerization based additive manufacturing techniques have several drawbacks that currently limit the applicability and scope of 3D printing, including: topological constraints, the requirement for numerous complex support structures that later need to be removed, long print times for complex geometries, relative motion between the liquid resin and printed part, as well as debilitating mechanical weakness and anisotropy resulting from the inherently layered structure of the parts. We propose and demonstrate a novel volumetric 3D printing technique based on one of the most ubiquitous computational imaging methods in the field: computed axial tomography. Computed axial lithography (CAL) is a vat photopolymerization technique that exposes the entire resin volume by projecting images from a multiplicity of angles. The technique is a physical implementation of the filtered back projection algorithm for tomographic reconstruction. We use constrained non-convex optimization in order to generate images that are projected into the resin in order to sculpt a 3-dimensional energy dose that cures the desired arbitrary geometry. This eliminates the requirement for supports and enables complex and nested structures that were previously challenging or impossible to print. Further, the process is layer-less and does not involve any relative motion between the resin and the printed part, which has positive implications for mechanically isotropic part strength. We demonstrate support-less printing of complex geometries containing 10^8-10^9 voxels in 2-4 minutes, orders of magnitude faster than comparable techniques.

Computational imaging is a new frontier of imaging technology that overcomes fundamental limitations of conventional systems by jointly designing optics, devices, signal processing, and algorithms. In this talk, I will first present recent advancements in high-throughput computational microscopy based on coded illumination and nonlinear phase retrieval, which enables wide field-of-view and high-resolution Gigapixel and 3D phase microscopy capability. Next, I will present a new neural network inspired framework for solving inverse scattering problems using recursive models to enable recovery of multiple scattering information in large-scale complex media. Such computational imaging approach creates significant new capabilities by integrating hardware and computation at the system level. It promises wide applications, such as biomedicine, metrology, and remote sensing.

Synchrotrons like the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory (LBNL) are an extremely bright source of X-rays. In recent years, this brightness has been coupled to large increases in detector speeds (including CMOS and sCMOS detectors) to enable microCT 3D imaging at unprecedented speeds and resolutions. The micro-CT Beamline at the ALS has been used by geologists simulating volcanic eruptions, engineers developing hierarchical materials that are tough at high temperature, and biologists studying water transport in plants experiencing drought stress. In each case, 3D processes occurring over seconds to minutes are studied with micrometer resolution-and in each case, advanced algorithms and data management have been critical in completing successful experiments. This article will describe the collaboration of the ALS with the National Energy Research Scientific Computing Center (NERSC) supercomputer to develop a super-facility, combining powerful X-rays with enormous computing power and describe the collaboration of the ALS with the Center for Applied Mathematics for Energy Research Applications (CAMERA) at LBNL to develop algorithms that can not only handle the enormous data sizes now being collected, but do so fast enough to give scientists feedback during their experiments in real-time. A major focus of CAMERA has been to apply new machine learning approaches to tomography, to improve image reconstruction, automate feature detection, and allow image search.

In mathematics and physics, a phase space of a dynamical system is a space in which all possible states of a system are represented, with each possible state corresponding to one unique point in the phase space. In partially coherent optical systems, the phase space is known as the Wigner distribution, representing simultaneously the values of the optical field in spatial and spatial frequency domains. Related to the notion of "etendue", the value of the optical field in phase-space is conserved and represents optical information. The world studied by mathematical projections is a process of linearization. At some level of approximation, the structure of details collapses into an average behavior, that is the linear relationship between two variables in a system. Hence cause-effect laws that are so common in the physical sciences are also seen in optics as theories of diffraction. A common approximation in denoting phase objects, is replacing them with purely imaginary value, according to the first term of the Taylor series approximation therein. This is of relevance in theories of phase contrast (eg. Zernike phase contrast), where the object is assumed to be purely imaginary, in scattering theories such as for photomasks in lithography, where scattering from thick mask edges is assumed to be imaginary valued, or in theories of weak speckle, where the speckle is used to image the contrast transfer function of the system. This approximation is akin to the weak object approximation, of Max Born and Rytov. A phase space description of linear assumptions in scattering is demonstrated, which is sensitive to both the coherence of light and the structure of the scatterer. The method can be extended to volumetric scattering, where light propagation is simply a shear in phase space, hence all optical processes are reduced to topological transforms of the underlying Wigner distribution. Using a weak phase object, interactions of symmetries of the imaging system corresponding to the symmetries of the scattered speckle shown by theory are also seen in experiments at optical and EUV wavelengths.

Significant advances in lithography and chip manufacturing in recent years have resulted in new challenges in metrology of electronic microdevices. Manufacturing process for the 10 nm node is already available and in combination with complex three-dimensional structured interconnections, there is a lack of methods for verification that the final products correspond to the original specifications. X-ray ptycho-tomography is a locally nondestructive imaging method that could potentially help to fill the gap between electron microscopy and conventional X-ray tomography. Quantitativeness of ptycho-tomography provides detailed device geometries and corresponding sensitivity to elemental composition through the complex-valued refractive index. In order to tackle the experimental challenges and improve the imaging quality, new computational methods need to be developed for both ptychography and tomography that can account for a wide range of imperfections such as sample drifts, illumination changes or sample changes during the scan. Here, we will mention the most important of them and possible ways how to deal with them.

Conventionally, the contrast of X-ray images is due to the attenuation of intensity of X-ray beams after penetrating materials, which is proportional to the imaginary part of the complex refractive index. Subtle density variations within soft tissue or other low-Z materials yield poor attenuation contrast. One method to improve the contrast of X-ray images is to utilize phase information since phase depends depend on the real part of the refractive index, which is typically 1000 times larger than the imaginary part. However, phase imaging relies critically on the spatial coherence of the X-ray beam which traditionally requires synchrotron sources, small-spot, low power laboratory sources, or precisely aligned gratings and multiple exposures. We will discuss two methods to achieve phase imaging with large-spot sources practical for clinical or security screening. The first method relies on using polycapillary optics to focus the beam and achieve the necessary coherence for traditional propagation-based phase imaging methods based on the transport of intensity equation. The second method relies on a coarse wire mesh which structures the illumination to enhance phase signatures and relax the coherence requirement. We will present recent results from both methods, including computational algorithms for phase contrast, phase retrieval and resolution enhancement.

Fourier ptychography is a computational imaging techniques that combines various full-field coherent images acquired under varied illumination angles and combined to yield a angular spectrum with a large synthetic numerical aperture and non-interferometric phase information. We present here the implementation of this technique in a full-field soft x-ray microscope designed to emulate modern EUV lithography tools imaging conditions, and we show that this technique can be used for the study of EUV photomasks. The technique allows us to quantitatively characterize phase defects (predominant in EUV lithography), to study new mask designs made of phase structures, to study sub-resolution assist features and extend the resolution of the microscope down to 26-nm, correspond to the N1 technology node.

Recently, the photon counting X-ray imaging / CT systems have been researched and investigated as a next generation imaging system. CdTe has high attenuation coefficient at hard X-ray (100keV<) for medical imaging system, and photon counting signal processing has very high sensitivity in theoretic. We have demonstrated the photon counting X-ray imaging / CT system by CdTe detectors. The high-contrasted CT images of acryl phantom were taken by this system. In this case, very low power X-ray source (150kV, 1.8uA) was used. CT images could not be reconstructed at low exposure condition less than 9.0uAs in this protocol using traditional CdTe detector, but we could obtain good images by using photon counting CdTe detector even if the very low exposure of 1.8uAs. Photon-counting CT is very powerful technique for low exposure X-ray imaging / CT system.

In this work we show how we can build a technology platform for cognitive imaging sensors using recent advances in recurrent neural network architectures and training methods inspired from biology. We demonstrate learning and processing tasks specific to imaging sensors, including enhancement of sensitivity and signal-to-noise ratio (SNR) purely through neural filtering beyond the fundamental limits sensor materials, and inferencing and spatio-temporal pattern recognition capabilities of these networks with applications in object detection, motion tracking and prediction. We then show designs of unit hardware cells built using complementary metal-oxide semiconductor (CMOS) and emerging materials technologies for ultra-compact and energy-efficient embedded neural processors for smart cameras.

A fundamental problem in imaging remote sensing systems is that of scale and resolution. The ability to resolve an object at a distance requires a high resolution sensor, with pixels subtending a small portion of the total field-of-view (FOV) of the imaging system. Traditional approaches to addressing this challenge are fundamentally data limited. To this end, we implemented foveating data reduction models inspired by the bi-foveated vision of birds of prey. The development of such systems for multiple target detection and tracking for air-to-ground target acquisition is important for several defense applications. The relative merits and disadvantages of various optical imaging technologies as well as several image transformations, sampling schemes, and object tracking algorithms were explored. Variable focal lens controlled by pressure, external voltage, or microfluidics demonstrate potential for devices requiring high resolution within a specified range. The distortion, coma, and spherical aberrations that occur can be corrected through the use of adaptive optics and custom 3D printed lenses. In conjunction with the hardware aspects, algorithmic approaches were also considered. The use of dynamically generated, moving foveal regions was investigated for use in motion tracking and object detection algorithms. Through the use of imaging systems with exceptionally large fields of view and localized areas of high resolution, machine vision systems can be implemented with less computational and data overhead. The implementation of our system is suited to use in either unmanned aerial vehicle or autonomous vehicle applications.

Recent research efforts on detector arrays in the near-infrared (NIR) and the short-wave infrared (SWIR) wavelength range have led to compact and robust 3D flash lidar architectures [1]. This technique can provide real-time 3D mapping of an area in various weather conditions for surveillance, but also for detection of moving objects in guidance of unmanned vehicles. Today main size limitation for compact, portable systems is the pulsed laser source. An alternative to solid-state or fiber lasers could be laser diodes since they have a better efficiency and their beam profile is compatible with active imaging by flash illumination. This paper will present recent advances in mJ class pulsed laser diodes made by Quantel Laser, France. Experimental results will be described both in NIR and in SWIR bands.

The DARPA Wafer-scale Infrared Detectors (WIRED) program requires the development of low cost detector technologies with high quantum efficiency and low dark current based on colloidal quantum dots (CQDs) of compound semiconductors. The program targets the SWIR (900 – 1700 nm) spectral range. This paper focuses on the design of 3 μm pitch, low noise ROICs for interfacing with SWIR CQD detectors. So far, the team has developed and demonstrated PV detector technology based on thin film CQDs IR-absorbing materials. The CQD films are deposited by spin-coating from solution directly on ROIC and fanout wafers at room temperature. The photodiode fabrication is fully compatible with CMOS fabrication at the wafer-level, allowing for large format FPAs limited only by the ROIC size. This paper outlines the preliminary design of a 3 μm pitch 1920 x 1080 modular ROIC, easily scalable to larger formats by mask stitching.

DRS has designed a full HD (1920x1080) readout integrated circuit (ROIC) specifically for cost-effective waferscale infrared (WIRED) detectors on 3 μm pitch, for best theoretical image quality optical system performance. The sensor’s pixels use a capacitive trans-impedance amplifier (CTIA) and a metal-insulator-metal (MIM) integration capacitor, to achieve 22 Ke- well capacity, 0.7 V output swing and 37 e- or 18 e- equivalent readout noise, operating at 60 Hz ripple readout mode or 30 Hz correlated double sampling (CDS) mode, respectively. The fully digital ROIC consumes approximately 0.5 W of power, allowing it to be fielded in battery-powered applications.

All material surfaces are covered with strong infrared/terahertz (IR/THz) evanescent waves since all materials contain positive and negative charges and the charge movement generates local electromagnetic waves at finite temperature. Previous theoretical analyses suggest that the thermal evanescent waves on metals and dielectrics are strongly localized within 100 nm from the surface, the energy density is more than 10000 times higher than the one of Planck’s radiation and their spectra lie in THz regions (wavelength: 8～20 μm). Probing such spontaneous evanescent waves with nanoscale spatial resolution can visualize the local dynamics of thermal equilibrium and non-equilibrium phenomena. Recently we have developed a passive scanning near-field optical microscope (SNOM), which probes surface evanescent waves without any external illumination. The microscope consists of a confocal infrared microscope, and an ultra-highly sensitive detector, named the charge-sensitive infrared phototransistor (CSIP, wavelength range is 14.5 ± 0.7 μm). In this presentation, we first describe the development of the passive SNOM. Then we show the results obtained with the SNOM; thermal evanescent waves on metals and dielectrics, and nanoscale distribution of evanescent waves derived from non-equilibrium phenomena in two dimensional electron gas. Our SNOM should open up a new way of investigating material surfaces in general and provide a novel technique of probing local temperature/electro-magnetic field distribution.

In this work we experimentally demonstrate high-performance narrowband terahertz (THz) bandpass filters through cascading multiple bilayer metasurface antireflection structures. Each bilayer metasurface, consisting of a square array of silicon pillars with a self-aligned top gold resonator-array and a complementary bottom gold slot-array, enables near-zero reflection and simultaneously close-to-unity single-band transmission at designed operation frequencies in the THz spectral region. The THz bandpass filters based on stacked bilayer metasurfaces allow a fairly narrow, high-transmission passband, and a fast roll-off to an extremely clean background outside the passband, thereby providing superior bandpass performance. The demonstrated scheme of narrowband THz bandpass filtering is of great importance for a variety of applications where spectrally clean, high THz transmission over a narrow bandwidth is desired, such as THz spectroscopy and imaging, molecular detection and monitoring, security screening, and THz wireless communications.

Silicon complementary metal oxide semiconductor (CMOS) technologies are arguably the most important asset in the world of electronics. Focal plane arrays (FPAs) are one of the driving forces in the revolution of low-cost, mass produced, compact, and high-resolution imaging devices. The importance of these imaging systems in the visible spectrum has highlighted the need of their implementation into other significant electromagnetic regions such as infrared (IR) and Terahertz (THz). The unique characteristics of THz waves make them ideal for a variety of important applications ranging from security and medical imaging, explosive and drug detection, and non-destructive quality control testing. These applications are possible due to the non-ionizing nature of THz radiation, its transparency to many non-conductive materials, and distinctive spectroscopic fingerprints of a vast number of substances.

Current THz imaging systems are usually restricted to laboratory use due the lack of compact, portable and roomtemperature operated sources and detectors. Therefore, the implementation of CMOS based THz detectors is key to promote the exploitation of low-cost, room-temperature, high-resolution, highly sensitive, and portable THz imaging systems. Here we present the monolithic integration of two types of THz FPAs fabricated in a standard 180 nm CMOS process. The imagers are composed of THz metamaterials (MM) absorbers coupled to a microbolometer, either vanadium oxide (VOx) or silicon pn diode, integrated with readout electronics to form 64 x 64 CMOS FPAs. The suitability of THz imagers for stand-off imaging of concealed objects was demonstrated in transmission mode by capturing images of metallic objects hidden in a manila envelope.

A wide range of chemical and biological agents - such as explosives, drugs, and tissues - have unique spectral signatures at THz frequencies, which can be unambiguously identified using THz imaging. Existing T-ray imaging technologies can be mainly categorized as pulsed THz time-domain imaging and CW THz imaging. For so many years, researchers have been striving to develop new technologies that could inherit the merits of both methods and offer a fast response to desired frequency bands for multispectral THz imaging, preferably in real time. While decent progress has been made in the THz sources (especially, QCLs), THz imaging technologies somehow lag behind mainly due to the fact that natural materials do not show much response in the THz frequency range. Metamaterials (MMs) - artificial structures in which the electromagnetic responses can be engineered by design to access a frequency range - can show strong responses in the THz regime, offering a flexible and relatively cheap route to image in THz using designer sensor imaging arrays based on MMs. The multicolor T-ray imaging setup using a THz hyperspectral MM-FPA and a set of QCL sources. The MM-FPAs, which absorb THz radiation at multiple bands (2.5 THz, 3.4 THz, and 4.3 THz here), can then be paired with the tunable QCL sources in accordance with different applications such as frequency selective material identification of concealed chemical substances and cancerous tissue diagnosis.

We analyze the information content of metasurface apertures in the context of a millimeter-wave computational imaging system. Each of the apertures consists of a waveguide- or cavity-backed metasurface layer, which produces a series of quasi-random field patterns as a function of the excitation frequency. The metasurface layer is a conducting surface patterned with subwavelength, metamaterial slots, each of which couples energy from the guided wave to the scene. A single measurement of a scene consists of illuminating the scene with a transmit aperture and detecting the back-scattered field at a receive aperture. Repeating this process over all combinations of transmit and receive apertures and over all frequencies produces a set of measurements that can be used to estimate the scene reflectivity using computational imaging methods. While the maximum number of independent measurement modes for a composite aperture is set by bandwidth and diffraction limits, the actual number of modes available from an aperture can be substantially smaller due to spatial correlation of the field patterns from one mode to another. To minimize this correlation, a variety of design steps can be taken, including optimizing the quality-factor of an aperture and optimizing the Fourier space coverage as determined by the specific number and arrangement of metasurface elements. These design considerations are quite general, and apply to a wide range of metasurface designs. We present several metasurface designs and show how their specific architecture relates to the overall imaging performance of the system.

Tunable THz metamaterials has shown great potential to solve the material challenge due to the so called “THz gap”. However, the tunable mechanism of current designs relies on using semiconductors insertions, which inevitably results in high ohmic loss, and thereby significantly degrades the performance of metamaterials. In this work, we demonstrate a novel tunable mechanism based on polymetric microactuators. Our metamaterials are fabricated on the surface of patterned pillar array of flexible polymers embedded with magnetic nanoparticles. The transmission spectrum of the metamaterial can be tuned as the pillars are mechanically deformed though applied magnetic field. Compared to previous semiconductor based tunable mechanism, our structure has shown much lower loss.

In the last ten years terahertz techniques have become increasingly common laboratory and industrial tools. This progress has been made possible by over thirty years of concentrated effort. In this talk we discuss our recent work combining time-domain terahertz imaging with advanced signal-processing to obtain unprecedented depth information in a nondestructive fashion about subsurface damage in both glass and carbon fiber composites and in coatings on metals. In addition, we present an example characterizing the stratigraphy of an art painting to illustrate the technique to measure thicknesses in a multilayer coating. Other optically opaque materials, including polymers, glass, textiles, paper, and ceramics, are transparent to terahertz radiation, and thus terahertz imaging may access information in these materials below the surface. Signal processing techniques are needed to unleash the power of terahertz imaging to measure thin layers of thickness on the order of 10 microns. These approaches permit us to gain information about thin layers that are obscured in the raw signals. That is, when the time duration of the terahertz pulses is longer than the optical delay to traverse a given layer, the terahertz echoes associated with reflections off the various interfaces may temporally overlap. Specifically, we have successfully employed frequency-wavelet domain deconvolution, sparse deconvolution, and autoregressive deconvolution for a range of problems.

The Office of Naval Research (ONR) Code 30 Explosive Hazard Defeat (EHD) program seeks to enhance the future combat capability of Naval Forces. Explosive hazards, mines and improvised explosive devices (IED) remain major obstacles that limit the freedom of maneuver and operational tempo in expeditionary operations both ashore and at sea. The desired capability is an explosive hazard defeat system capable of standoff detection and neutralization, combined with proofing, marking and reporting capabilities from the Very Shallow Water (VSW) through the Surf Zone (SZ), Beach Zone (BZ) and on to the inland objectives.

These environments provide many challenges to current sensors and sensing systems. Most optical sensors suffer degradation of performance due to low visibility in turbid water and the surf zone area. They also lack ability to find buried or hidden objects. Various RF based sensor systems demonstrate the ability to detect and image hidden and buried objects, but attenuation in water makes them almost impossible to operate through the water. Active magnetic detection operates both ashore and underwater, but the range is limited. Biological sensors and synthetic biology also show potential as solutions. The solution resides in multiple sensors that address disparate environmental and target challenges as a system. Recent development in autonomy and proliferation of small unmanned platforms allow new distributed and autonomous operational concepts that utilize unmanned platforms to gain safe standoff distance. This paper plans to present the future operational environment challenges and research and development opportunities.

When an intense ultrafast laser pulse is focused into a free-flowing water film, broadband terahertz (THz) radiation is emitted through the interaction between strong laser fields and liquid water molecules. Experimental results show that THz waves generated from liquid water have very different characteristics in comparison to those from other THz sources such as solids and gases. The mechanism for the THz wave generation process is currently attributed to the plasma formation in the bulk water. This demonstration may find potential applications in biological imaging and provide new tools in the field of nonlinear laser-liquid interactions.

Numerical computation using HFSS finite element analysis was conducted in order to determine the dispersion relation (complex index) of the surface plasmon polariton (SPP) mode. SPP result from the interaction or coupling between electromagnetic fields in the form of light and delocalised electrons on a metal interface. SPPs has the effect of confining electromagnetic radiation on the order that is smaller than the wavelength. In this work, the correspondence by H.P Hsu (IEEE Trans. Microw. Theory Techn., 11(4), (1963).) was used in the study of SPP modes comparing both analytical calculations and numerical calculation from ANSYS HFSS to ascertain the veracity of the correspondence for SPP surface waves, and calculating the attenuation coefficient using quality factor, Q, obtained from HFSS eigenmode calculations. Silicon dioxide and silver with the use of measured complex permittivity for silver is used to conduct this study. Numerically-obtained results for propagation length and SPP effective index are compared to analytical calculations from the well-known SPP dispersion relationship.

Curved image sensors offer a new degree of freedom in optical system design that promise low-cost, small-volume solutions for wide field-of-view imaging. Stretchable polymer backplanes can provide the high-density of interconnects and tolerate the large deformations needed to transform planar, wafer-based image sensors into shapes with large nonzero Gaussian curvature. Here we demonstrate a thermoformable backplane based on glycolated polyethylene terephthalate (PETg) that can be deformed to a 98° spherical cap with 0.5” radius. We introduce a process to integrate such backplanes with a CMOS image sensor and release the circuit from the wafer to form a monolithically integrated image sensor that can be thermoformed to the desired shape.

The Group for Quality Assurance and Industrial Image Processing has built a new experimental setup to characterize cameras and image sensors according to EMVA1288 standard. Next to the investigation of SLN (Sensitivity-Linearity- Noise) and spatial non-uniformities, the new test bench also provides an examination of the temperature dependence of sensors. The temperature dependent dark current produces an undesirable signal which affects the image quality negative and thus has to be known. It is caused by thermally induced electrons and increases linearly with exposure time as well as exponentially with temperature. To measure the dark current, it is necessary to vary and determine the temperature of the sensor. This was made possible by a climate chamber with a Peltier element, which enables a heating and cooling of the camera. An infrared sensor allows a contact-free detection of the actual camera temperature. Furthermore, the light source was improved for the new test bench. With the installed custom light source and integration sphere a homogeneous irradiation up to 97% is ensured. This way better results in tests were achieved. The light source with variable filter housing enables the use of monochromatically light in a wavelength range of 350 – 1700nm. A live monitoring of the irradiation during the image capturing is possible. A MATLAB script assists in the configuration of the camera, the measurement and the data storage. The user is guided step by step through the program. At the end of the measurements an automated evaluation follows, which illustrates graphs and parameters in a streamlined and print-ready format.

Reflection spectroscopy is a promising measuring principle to get measurement data of surface signatures from objects and materials. A large field of applications, in inline or outline testing tasks, can be handled with it. The investigation deals with investigations regarding development of a broadband UV radiation source and the integration in a hyperspectral push broom imaging system using standard spectral radiation sources. Comprehensive market research has shown that there is no disposability of a UV radiation source, which emits a nearly continuous radiation in the spectral range of 220 up to 400 nanometers. Therefore, a second idea is to combine various gas discharging lamps to receive a nearly continuous spectrum in that area of the UV radiation. A very important and interesting circumstance of using standard spectral lamps as a radiation source for push-broom-imaging is the fact, that the active zone of the plasma discharge has a line-like contour, which can assumed as an axially expanding point light source. Therefore, it is only necessary to project this for getting the needed radiation field in the framework of reflection spectroscopy. The aim is to determine which different gases of a standard range of spectral light sources are suitable. Another approach is the investigation of the effect that modifiable parameters – such as pressure or a time modulated energy source - might have to the spectral behavior of the differing radiation sources and the reflected light from the test object as well. Physical models of high intensity discharging light sources are well proved, but the concept of light addition, to get a special required spectral distribution, may cause some specific problems that must be solved. It is also a goal to evaluate, in which conditions classic models work and how far the can be used.

This contribution presents the design and simulation of finite size narrow band transmission filters for applications in realtime and remote short wave infrared (SWIR) spectroscopy and imaging. The results can ultimately be extended to hyperspectral imaging that has gained interest in many fields ranging from agriculture to surveillance. As chemical compounds possess unique set of sharp spectral signatures, they can be differentiated using wideband spectral scanning. However, such standard approaches require bulky instruments and long acquisition times together with post-processing of acquired data. These technological bottlenecks result in a diminished usefulness of such systems in scenarios demanding short response times, such as law enforcement, homeland security, and military applications. To overcome these limitations, narrow-band and pixel-size filters can be incorporated to focal plane arrays for real-time spectral imaging systems. In this study, we explored several designs of narrow-band, finite-sized (<10λ) SWIR transmission filters based on one dimensional and two dimensional guided mode resonance (GMR) gratings. The filter designs utilize dielectrics such as SiO₂ and TiO₂ and are optimized for high throughput for a narrow transmission band (~ 10 nm) within a large stop band (~ 500 nm). The electric field, fringing fields, and transmission response are investigated utilizing HFSS, CST, and Matlab software for normal incidence (dielectric losses accounted for in simulations). The fringing fields at the edges are also explored for various thicknesses of conductive reflectors fencing the filter edges. Tunability of the filters are also presented as a function of their design features, including dielectric thicknesses, grating periodicity, and grating duty cycle.

Graphene has been well studied to be an excellent thermoelectric (TE) material of choice for thermal detection. It is widely considered a key enabler for next-in-class infrared (IR) detectors given its superb carrier mobility, sensitivities and broadband absorption in far-IR range surpassing that of current thermopiles. Normally, TE studies are conducted using graphene exfoliated from graphite crystal. It is then transferred onto Si/SiO₂ substrate and fabricated into Hall bar configuration with microheater at one end. A gate voltage (Vg) is passed through the substrate and the response is examined in vacuum condition. By tuning the Vg, one can possibly obtain different thermoelectric power (TEP) values. The challenge is to maintain optimum Vg for the TE device to function which requires higher power consumption. This translate to the need for additional power supply. In this report, we proposed CVDG as TE material. Typically, CVDG are synthesized on Cu film and eventually transferred onto Si/SiO₂ substrate. The benefit of CVDG is that it is large area, relatively inexpensive and does not require a Vg with associated circuitry. For the first time, CVDG system was extended to nonvacuum condition to simulate open detector system where detector is exposed to sensing environment. Average TEP was measured to be 168μV/K at 298K. Moreover, CVDG is tested to be stable in air over several months with little or no decrease in performance. A comprehensive characterization between exfoliated and CVDG will be presented. In addition, measurement results for vacuum and non-vacuum detector mode will be compared as well.

X-ray imaging is popular in medical imaging, non-destructive testing and security. Main techniques of X-ray imaging with semiconductor detectors are charge accumulation and photon counting, and the photon counting is expected to identify materials at the same time with taking X-ray photograph by using energy information of X-ray photons. We proposed a direct charge handling method to build a photon counting system with energy information for X-ray imaging. This method operates the charge from the X-ray detector and converts it to encoded digital bit pattern directly without dead time of the front-end circuit. We simulated and built a proposed system to prove operating principals.