The NASA Jupiter Europa Orbiter (JEO) conceptual payload contains a thermal instrument with six different spectral bands ranging from 8μm to 100μm. The thermal instrument is based on multiple linear arrays of thermopile detectors that are intrinsically radiation hard; however, the thermopile CMOS readout needs to be hardened to tolerate the radiation sources of the JEO mission. Black Forest Engineering is developing a thermopile readout to tolerate the JEO mission radiation sources. The thermal instrument and ROIC process/design techniques are described to meet the JEO mission requirements.

Raytheon Vision Systems (RVS) has developed a family of high performance large format infrared detector arrays whose detectors are most effective for the detection of long and very long wavelength infrared energy. This paper describes the state of the art in mega-pixel Si:As Impurity Band Conduction (IBC) arrays and relevant system applications that offers unique off-the-shelf solutions to the astronomy community. Raytheon's Aquarius-1k, developed in collaboration with ESO, is a 1024 × 1024 pixel high performance array with a 30μm pitch that features high quantum efficiency IBC detectors, low noise, low dark current, and on-chip clocking for ease of operation. This large format array was designed for ground-based astronomy applications but lends itself for space based platforms too. The detector has excellent sensitivity out to 27μm wavelength. The readout circuit has several programmable features such as low gain for a well capacity of 11 × 10⁶e-, high gain for a well capacity of 10⁶e- and a programmable number of outputs (16 or 64). Programmable integration time and integration modes, like snapshot, rolling and non-destructive integrations, allow the Aquarius to be used for a wide variety of applications and performance. A very fast full frame rate of 120Hz is achieved with 64 outputs (32 outputs per side) and a programmable centered windowing will accommodate a wide range of readout rates. The multiplexer and packaging design utilizes two alignment edges on the SCA which can be butted on two sides for expansion to 2k × 1k and wider focal planes. Data is shown on several focal plane arrays to demonstrate that very low noise and high quantum efficiency performance has been achieved. This array leverages over thirty years of experience in both ground and space based astronomy sensor applications. The technology has been successfully demonstrated on programs such as NASA's Spitzer Space Telescope and Japan's Akari Space Telescope, and will be used on the Mid-Infrared Instrument (MIRI) aboard the James Webb Space Telescope (JWST).

The Blocked Impurity Band (BIB) detector technology team at DRS Sensors and Targeting Systems specializes in providing the highest performance, broadest application range of BIB detector products. These include detectors, Focal Plane Arrays (FPA), and sensor assemblies for ground, airborne and space applications. We offer flight proven low flux Si:As and Si:Sb FPAs in square formats up to 1024x1024. We also offer high-flux FPA systems for ground-based telescopes and airborne applications in several square and rectangular formats, such as 160×640 sensors for push-broom spatial-spectral imaging. NASA's Wide-field Infrared Survey Explorer mission selected DRS 1024×1024 arrays for its the 12 and 24 micron wavelength bands. The Spitzer Space Telescope utilizes DRS 128×128 Si:As and Si:Sb FPAs, and 1024×1024 Si:Sb arrays are being fabricated by DRS for an upgrade to the SOFIA FORCAST instrument. DRS is unique in providing detectors and FPAs in alternate detector materials such as Si:Sb, Si:Ga, and Si:P to optimize wavelength range vs operating temperature. Sensor assemblies include detectors or FPAs packaged with cryogenic cabling and electronics and ambient temperature drive and data acquisition electronics--fully tested, and environmentally qualified. DRS is also unique in extending its conventional BIB detector product line to include novel detector architectures for a variety of applications. Si:As detectors with avalanche gain (~40,000X) function as number-mode photon counters at visible or mid-infrared wavelengths. A recent DRS innovation is the extension of Si:As BIB detectors designs to achieve wavelength extension into the far-infrared (low THz) wavelength region. Wavelength extension to ~50 microns (6 THz) has been demonstrated, with further extension to at least ~100 microns (3 THz) in progress.

Over the last several years the development of type-II Strained Layer Superlattice (SLS) infrared photodetectors has yielded devices that may offer plausible alternative technology to conventional mercury cadmium telluride (MCT)-based photodetectors. Prevailing theory predicts that SLS-based detector technologies will have several potential advantages over MCT technologies, including lower dark currents and higher operating temperatures. However, experimentally it has been found that conventional p-on-n and n-on-p SLS detectors have high dark current and thus, do not reach theoretically predicted performance benchmarks. The two prevailing contributors to this high dark current are the generation-recombination (GR) current and surface leakage currents, the latter resulting from the mesa sidewall exposure. A recently emerging technology that utilizes a uni-polar barrier design nBn has been shown to reduce dark current, while keeping the inherent advantages of SLS. Specific advantages of SLS over MCT include wavelength tunability, improved uniformity, and operability potentially at a reduced manufacturing cost. This report presents some recent experimental findings for the electrical and optical response of an nBn detector composed of an InAs/GaSb SLS absorber (n) and contacts (n) with an AlGaSb barrier (B). Results include the intrinsic determination of the diffusion current, and the GR current for the nBn device. Also presented is the optical response of the InAs/GaSb nBn detector at 77K over a broad range of operating biases. Dark current measurements over the 10K-300K temperature range were undertaken to extract the activation energies in the heterostructure.

It is known that ultra-fast laser is able to change solids physical state: to melt, to evaporate, to ionize. It is less known that ultra-fast laser is able to change semiconductor optical state: to bleach it. Such short time changes in semiconductor optical characteristics depend on the bandgap structure, therefore we are introducing the term - Ultrafast Bandgap Photonics. Phenomena of Ultrafast bandgap photonics are time-dependent and the optical effects are reversible: ultra-fast laser "bleaches" semiconductor and temporally changes spectral reflectivity, absorptivity, and transmittance as well as polarization characteristics. Applications of Ultra-fast bandgap photonics are remote control of semiconductor characteristics and material properties. Ultrafast Bandgap Photonics effects may temporally alter photodetector's fundamental characteristics - responsivity and detectivity as well as its response time and spectral bandwidth - all of these may happen without changes in photodetector electrical response. While Ultrafast Bandgap Photonics applications are directly depend on pulse dwell time and pulse repetition rate; it is important to say that laser energy per pulse should be carefully managed. In this paper we discuss some foundations of ultra-fast bandgap photonics - specifically for low pulse energy ultrafast laser.

Our fundamental approach was to increase the operating temperature of the device by reducing the volume of its diffusion region, while maintaining the performance at low temperatures. Reducing the diffusion volume of a detector can be achieved by reducing the active layer thickness, reducing the absorber volume, and reducing the junction area while maintaining the optical area as the original pixel by using micro-lens technology on pixel levels, etc. We are pursuing an infrared device with a unique planar architecture that uses a novel approach in obtaining low arsenic doping concentrations in longwavelength (LW) mercury cadmium telluride (HgCdTe) on CdZnTe substrates for higher temperature applications. We fabricated a p-on-n structure that we term P+/p/N+, where the symbol "p" indicates a drastically reduced extrinsic p-type carrier concentration (on the order of mid-10¹⁵ cm^-3); P⁺ and N⁺ denote a higher doping density, as well as a higher energy gap, than the photosensitive base p-region. Fabricated devices indicated that Auger suppression is seen in the P⁺/p/N⁺ architecture at temperatures above 130 K; we obtained saturation currents on the order of 3 mAmps on 250-μm-diameter devices at 300 K with Auger suppression. Data shows that roughly 50% reduction in dark current is achieved at 300 K due to Auger suppression.

Multi-spectral sensor systems that record spatially and temporally registered image video have a variety of applications depending on the spectral band employed and the number of colors available. The colors can be selected to highlight physically meaningful portions of the image, and the resulting imagery can be used to decode relevant phenomenology. For example, the images can be in spectral bands that identify materials that are intrinsic to the target while uncommon in the backgound, providing an anomaly detection cue. These multi-spectral video sensor engines can also be employed in conjunction with conventional fore-optics such as astronomical telescopes or microscopes to exploit useful phenomenology at dissimilar scales. Here we explore the relevance of multi-spectral video in a space application. This effort coupled a terrestrial multispectral video camera to an astronomical telescope. Data from a variety of objects in Low Earth Orbit (LEO) were collected and analyzed both temporally, using light curves, and spectrally, using principal component analysis (PCA). We find the spectral information is correlated with temporal information, and that the spectral analysis adds the most value when the light curve period is long. The value of spectral-temporal signatures, where the signature is the difference in either the harmonics or phase of the spectral light curves, is investigated with inconclusive results.

In this study the material quality and optical properties of type II InAs/GaSb superlattices are investigated using transmission and photoluminescence (PL) spectroscopy. The influence of the material quality on the intensity of the luminescence and on the electrical properties of the detectors is studied and a good correlation between the photodetector current-voltage (IV) characteristics and the PL intensity is observed. Studies of the temperature dependence of the PL reveal that Shockley-Read-Hall processes are limiting the minority carrier lifetime in both the mid-IR wavelength and the long-IR wavelength detector material studied. These results demonstrate that PL spectroscopy is a valuable tool for optimization of infrared detectors.

High resolution imaging in the UV band has a lot of applications in Defense and Commercial Applications. The shortest wavelength is desired for spatial resolution which allows for small pixels and large formats. UVAPD's have been demonstrated as discrete devices demonstrating gain. The next frontier is to develop UV APD arrays with high gain to demonstrate high resolution imaging. We also disuses our recent efforts on development of APD's using MOCVD of GaN/ AlGaN. We present an analytical model that can predict sensor performance in the UV band using p-i-n or APD detectors with and without gain and other detector and sensor parameters for a desired UV band of interest. SNR's can be modeled from illuminated targets at various distances with high resolution under standard MODTRAN atmospheres in the UV band using detector arrays with unity gain and with high gain APD along with continuous or pulsed UV lasers.

SiGe based focal plane arrays offer a low cost alternative for developing visible- near-infrared focal plane arrays that will cover the spectral band from 0.4 to 1.6 microns. The attractive features of SiGe based foal plane arrays take advantage of silicon based technology that promises small feature size, low dark current and compatibility with the low power silicon CMOS circuits for signal processing. This paper will discuss performance characteristics for the SiGe based VIS-NIR Sensors for a variety of defense and commercial applications using small unit cell size and compare performance with InGaAs, InSb, and HgCdTe IRFPA's. We will present results on the approach and device design for reducing the dark current in SiGe detector arrays. We will discuss electrical and optical properties of SiGe arrays at room temperature and as a function of temperature. We will also discuss future integration path for SiGe devices with other Silicon-based technology for defense and Commercial Applications.

Ferroelectric oxide ceramics have been investigated as possible alternatives to highly sensitive triglycine sulfate (TGS) crystals for their use in room temperature infrared detectors. In this paper dielectric and pyroelectric properties of some ceramics based on modified lead titanate and others are presented. The figures-of-merit of these ceramics calculated using the measured dielectric and pyroelectric data are presented. The relative advantages and disadvantages of the principal ceramic systems are also compared with existing materials reported in the literature.

We report current-voltage data for back-illuminated mesa photodiode test structures fabricated by arsenic-diffusion into n-type LPE HgCdTe films. Arsenic diffusion was carried out in a sealed quartz ampoule containing a source of both Hg and As. The arsenic-diffused p-on-n photodiodes were characterized at 70 K and 80 K. The cutoff wavelength was about 11 μm at 80 K. The data for 400 μm diameter photodiodes fabricated by the arsenic diffusion process are very similar to those from a conventional two-layer LPE P-on-n process for material with approximately the same cutoff wavelength. We outline process and doping level changes that should improve detector performance.

In this paper we present a full three-dimensional numerical simulation of Arsenic-diffused HgCdTe based planar pixel arrays intended for detection in the medium- and long-wavelength infrared spectral range. As-diffused planar detector array structures, as opposed to mesa-type structures, do not require any etching processing that causes surface damages and consequently may lead to detector arrays with higher performance than the mesa type. Because of the interest in high performance planar infrared focal plane arrays, it is critical to develop numerical simulation models useful to predict the array's performance before they are fabricated. The goal of this work is to study the dependence of the quantum efficiency and the pixel-to-pixel cross talk on the geometrical and material parameters.

Characteristics of transparent PLZT ceramics can be tailored by controlling the component of them, and therefore showed excellent dielectric, piezoelectric, pyroelectric and ferroelectric properties. To integrate the ceramics with microelectronic circuit to realize integrated applications, the ceramic wafers have to be thinned down to micrometer scale in thickness. A7/65/35 PLZT ceramic wafer was selected in this study for the thinning process. Size of the wafer was 10×10mm with an initial thickness of 300μm. A novel membrane transfer process (MTP) was developed for the thinning and integration of the ceramic wafers. In the MTP process, the ceramic wafer was bonded to silicon wafer using a polymer bonding method. Mechanical grinding method was applied to reduce the thickness of the ceramic. To minimize the surface damage in the ceramic wafer caused by the mechanical grinding, magnetorheological finishing (MRF) method was utilized to polish the wafer. White light interference (WLI) apparatus was used to monitor the surface qualities of the grinded and ploished ceramic wafers. For the PLZT membrane obtained from the MTP process, the final thickness of the thinned and polished wafer was 10μm, the surface roughness was below 1nm in rms, and the flatness was better than λ/5.

The property of pyroelectric material finds application in infrared detection. A study was conducted to investigate the effect of inclusion of volcanic ash into cement and bonded with polyvinyl alcohol (PVA) giving cement:volcanic-ash systems. The ash used in this experiment is from the eruption of the Soufrière Hill volcano in the island of Montserrat, West Indies. Preliminary results indicate that cement: volcanic ash systems shows pyroelectric effect. Further investigations were carried to determine the effect of temperature and frequency on the variation of dielectric properties. The results show that both dielectric constant and ac conductivity of cement decrease with inclusion of volcanic-ash.

It has long been proven that pyro-optical properties can be used to develop high performance IR detectors without making use of a microelectronic readout circuit. In this application, the sensing materials should have high pyro-optic coefficient, or the refractive index of the materials should have strong dependence on temperature. Polymers showed higher pyro-optic coefficient compared with that of most inorganic materials. Among the polymers, liquid crystals (LCs) attracted more interests for their stronger temperature dependent optical characteristics. In this study, 5CB and 3HHV LCs were selected as examples to investigate their pyro-optic properties for the development of optical readout IR imaging devices. Refractive indices of the 5CB LC for both ordinary and extrodinary light were characterized within the phase transition temperature range. It was found that the no changed slightly with the variation of temperature, while the ne changed dramatically with the change of temperature. For 5CB, when the temperature increased from 22°C to 34 °C, n_e decreased from 1.75 to 1.64 for wavelength of 632.8nm. Results for 3HHV were also reported and analyzed. Another interesting property of the 5CB was that it showed obvious IR absorption in the wavelength range between 3 and 5 μm, which made them more promising for the application as IR sensing materials.

After introducing the uncooled infrared imaging based on a novel bi-material cantilever, this article emphasize on an optical system of an IR imaging prototype. At first, we select the structure form of optical system. Our optical system prototype consists of an imaging optical component and an optical readout component. The optical readout component comes from 4f' optical system and has been made some improvement to reduce its size, weight and power consumption. Then we measure and analyze the parameters of the FPA and CCD, in order to determine the geometrical sizes and the aberration requirement for every lens. At last we report on the implement of the prototype. The imaging result is showed in this paper. Experimental results indicate that the NETD of this system is less than 200mK.

Based on the invention of the photocell four German organizations forced the development of electrooptics in Germany: Allgemeine Electrizitaetsgesellschaft in Berlin, Zeiss in Jena, Elektroakustik in Kiel and the German Reichspost in Berlin. The outcome of this effort were: image converters with alkali and semiconductor photocathodes, infrared homing devices for anti aircraft missiles and heat bearing devices. These devices were used for instance in the German tank no. 5 Panther, the anti aircraft missiles Enzian and Schmetterling and for the coastal defense of Denmark. It is interesting to know that the infrared homing device of the sidewinder rocket is based on that of the Enzian.

Using the Simultaneous Multiple Surface method in 2D (SMS2D), we present a fast catadioptric objective with a wide field of view (125°×96°) designed for a microbolometer detector with 640×480 pixels and 25 microns pixel pitch.

The progress of MEMS-based uncooled infrared focal plane arrays (IRFPAs) are one of the most successful examples of integrated MEMS devices. We report on the fabrication and performance of a MEMS IRFPA based on bimaterial microcantilever. The IR images of objects obtained by these FPAs are readout by an optical method. However, it is difficult to avoid unwanted shape distortions in fabrication, which can degrade image quality in many ways. In this paper, the actual manufacturing errors of FPA are widely and deeply analyzed. There are basically two kinds of manufacturing error. The limitations of both kind of error are given. It is alse pointed out that the detecting sensitivity has its special complexity if the shape of the FPA is not ideal flat. To overcome the difficulties in readout process caused by manufacturing errors, a novel holographic compensating illumination technology was given. The possibilities of actualizing this technology are analyzed in many aspects. And a model of computer generated holographic compensation is given as a further development to be actualized in future The experiment shows that it is a feasible way to improve system performance, especially when it is too difficult to perfect the techniques of an FPA fabrication.

We describe a means for improving the performance of CMOS image sensors using vertical waveguides, known as light pipes. We describe experimental results on the etching of silicon nitride pillars, and the fabrication of photodiodes.

This paper reviews recent European developments in imaging photomultiplier technology. Photocathode technology is well established and has been optimised for a variety of applications; for example, the multi alkali cathode has deep UV response optimised for Cerenkov detectors in particle physics and also for use in UV laser inspection systems. Telluride based cathodes have been substantially improved for both astronomical and solar blind imaging systems. Recent developments have significantly advanced the time resolution limits of MCP based photomultipliers; this is of particular importance for applications in nuclear physics. The same technology is driving multi-pixel photomultiplier developments for biological applications.

Single-photon avalanche diodes (SPADs) are nowadays the most consolidate solid-state alternative to photomultiplier tubes and time-correlated single-photon counting. Optical benches are used for the characterization of the noise figures of these detectors, including dark count, afterpulsing effects and cross-talk. With accurate optical setups it is possible to obtain resolutions down to 5 microns, but with today's technologies, this spot size can cover more than one single pixel. Moreover, on other common and envisaged applications like particle detection in Nuclear and High Energy Physics or as silicon photomultipliers for Cerenkov telescopes, this does not allow to observe what happens when a charge is generated between consecutive pixels. This work presents the innovative characterization of single-photon detectors with the aid of the electron beam generated in a dual beam FIB/SEM apparatus. A simple setup allows a very good control of the dose and the spot down to 5 nm at 30 keV, The characterization has been proven in photodetectors fabricated in a standard CMOS technology. The results have been validated by comparison with those obtained by optical setups, with simulation with PENELOPE (Penetration and Energy Loss of Positrons and Electrons) and by technology simulations with ISE-tCAD.

There is a growing need in scientific research applications for dual-mode, passive and active 2D and 3D LADAR imaging methods. To fill this need, an advanced back-illuminated silicon avalanche photodiode (APD) design is presented using a novel silicon-on-sapphire substrate incorporating a crystalline aluminum nitride (AlN) antireflective layer between the silicon and R-plane sapphire. This allows integration of a high quantum efficiency silicon APD with a gallium nitride (GaN) laser diode in each pixel. The pixel design enables single photon sensitive, solid-state focal plane arrays (FPAs) with wide dynamic range, supporting passive and active imaging capability in a single FPA. When (100) silicon is properly etched with TMAH solution, square based pyramidal frustum or mesa arrays result with the four mesa sidewalls of the APD formed by (111) silicon planes that intersect the (100) planes at a crystallographic angle, φ c = 54.7°. The APD device is fabricated in the mesa using conventional silicon processing technology. The GaN laser diode is fabricated by epitaxial growth inside of an inverted, etched cavity in the silicon mesa. Microlenses are fabricated in the thinned, and AR-coated sapphire substrate. The APDs share a common, front-side anode contact, and laser diodes share a common cathode. A low resistance (Al) or (Cu) metal anode grid fills the space between pixels and also inhibits optical crosstalk. SOS-APD arrays are flip-chip bump-bonded to CMOS readout ICs to produce hybrid FPAs. The square 27 μm emitter-detector pixel achieves SNR > 1 in active detection mode for Lambert surfaces at 1,000 meters.

The attributes of the scientific-grade 4k linear CID51 sensor are presented. The CID51 sensor is fabricated using 0.18 μm technology. The 0.18 μm design rules permit proximity-coupling of the two photogates within the pixel required for non-destructive readout of the charge. The 14 μm by 50 μm pixels are arranged on two evenly staggered 2080-pixel rows. The result is a randomly addressable 4160 pixel array with an effective pitch of 7 microns and an effective height of 100 microns. The sensor incorporates parallel pixel processing with on-chip correlated double sampling. The critical unique feature of the CID51 is the 32 analog row storage registers (RSR) per pixel. These RSRs allow for the time resolved sampling of the 4160 pixel spectrum and can be randomly read out at rates as high as 8 MHz. The signal storage of up to 32 samples per pixel is non-destructive allowing for the integration of spectroscopic events with unprecedented microsecond time resolution. Alternatively, because pixels can be randomly accessed for readout or reset, intensely illuminated pixels can be quantitatively sampled and rapidly cleared of photon-generated charge, while weakly illuminated pixels are simultaneously allowed to integrate. Thus, the effective integration time can be varied from pixel to pixel based upon the observed photon flux vastly expanding dynamic range. Full spectrum acquisition provides all of the spectral content, including background continuum information for accurate photometry and spectrum to spectrum calibration. The CID51 device is suited for scientific applications demanding high dynamic range and/or time resolved capabilities.

In this paper we present radiation studies performed on a low-noise, high-speed, large-area CMOS image sensor (CIS) based on the 0.18 μm CMOS process. The sensor has 2560(H) × 2160(V) pixels with a readout speed of 100 frames/sec and a readout noise of less than 2 e- rms. The sensor features 5T pinned photodiode pixels on a 6.5 um pitch. In order to measure the impact of radiation exposure on the sensor performance, the device was subjected to x-ray exposure of 50 kRads of incident radiation using a broad band 50 KVP x-ray source to assess Total Ionizing Dose (TID) sensitivity. The active area and the digital control block and amplification circuitry were separately irradiated to evaluate the damage to each. Dark data was captured as a function of radiation dose in order to measure dark current and offset changes in the signal.

Current generation analog and photon counting flash lidar approaches suffer from limitation in waveform depth, dynamic range, sensitivity, false alarm rates, optical acceptance angle (f/#), optical and electronic cross talk, and pixel density. To address these issues Ball Aerospace is developing a new approach to flash lidar that employs direct coupling of a photocathode and microchannel plate front end to a high-speed, pipelined, all-digital Read Out Integrated Circuit (ROIC) to achieve photon-counting temporal waveform capture in each pixel on each laser return pulse. A unique characteristic is the absence of performance-limiting analog or mixed signal components. When implemented in 65nm CMOS technology, the Ball Intensified Imaging Photon Counting (I²PC) flash lidar FPA technology can record up to 300 photon arrivals in each pixel with 100 ps resolution on each photon return, with up to 6000 range bins in each pixel. The architecture supports near 100% fill factor and fast optical system designs (f/#<1), and array sizes to 3000×3000 pixels. Compared to existing technologies, >60 dB ultimate dynamic range improvement, and >104 reductions in false alarm rates are anticipated, while achieving single photon range precision better than 1cm. I²PC significantly extends long-range and low-power hard target imaging capabilities useful for autonomous hazard avoidance (ALHAT), navigation, imaging vibrometry, and inspection applications, and enables scannerless 3D imaging for distributed target applications such as range-resolved atmospheric remote sensing, vegetation canopies, and camouflage penetration from terrestrial, airborne, GEO, and LEO platforms. We discuss the I²PC architecture, development status, anticipated performance advantages, and limitations.

CCD as well as CMOS pixels suffer from the drawback of limited dynamic range and hence are unable to capture the wide dynamic range available in nature. Attempts to make wide dynamic range pixel have concentrated on either multiple capture techniques or the weak inversion region of a MOS device thereby producing a logarithmic response. The later is preferred on account of its similarity to the response of human eye. However, the response to brightness in the human eye more closely follows the Steven's power law. In this paper, a CMOS pixel is presented which is capable of producing a wide dynamic range response similar to that of the Steven's power law of brightness. In addition to this response, this 4-transistor pixel designed and manufactured in standard CMOS process has the ability to change the exponent as well as the proportionality constant in its response during its operation (run time). The pixel incorporates a single transistor used as compare and cutoff switch in addition to the standard active pixel sensor circuitry. The integrated response of the pixel is constantly compared to an inverted Steven's law response curve thereby leading to the required response. On account of small transistor count, the pixel has similar fill-factor and quantum efficiency as that of a standard CMOS active pixel sensor.

In range-resolved reflective tomography laser radar imaging system, different objects surfaces have a major impact on signals reflected, and the corresponding different filters in filtered back-projection algorithm would attenuate varying degree artifacts in the resulting images reconstructed. In this paper, light reflection from a surface is described by the Stanford-Robertson bidirectional reflectance distribution function (SR BRDF) model developed by the Air Force. Different reflective parameters in SR BRDF were assumed to simulate various surfaces with different proportion between diffuse reflection and specular reflection. The projections of objects were simulated with 1 degree view increment covering the entire angular domain. We also add the experimental imaging results to validate the effectiveness of this SR BRDF model in reflection tomography. Several filters with different parameters were applied and the quality of images reconstruction was compared, especially beam hardening artifacts and the crossed streak artifacts.

Range-resolved reflective tomography using short pulselength lasers has been shown to be an image reconstruction method which can be used to recover image information about an object with a non-imaging laser radar (ladar) system. The resulting time-dependent return signal (Project) is collected by a non-imaging optical system, which provides a onedimensional signal as a function of range. The resulting time-dependent return signal is collected by a non-imaging optical system, which provides a one-dimensional signal as a function of range. This one-dimensional signal is related to a one-dimensional slice of the spatial 3-D Fourier transform of the object. Consequently, the resolution of the object remains constant, regardless of the object's distance from the optical system. This paper presents the field results of a short pulselength direct-detect laser reflective tomography imaging ladar, and gives the image reconstruction results. The intervals of the projections are different because of the variable speed of the imaging object. In order to efficiently improve and modify the image reconstruction quality in the field experiments, we develop a new imaging reconstruction algorithm based on the feature point in the projection data to overcome the nonuniform intervals between adjacent projections. The experiment results show our algorithm is feasible and efficient.

This paper discusses about a readout circuit for Dual-Band Quantum Well Infrared Photo-detectors (DBQWIP) interlaced focal plane array infrared image system. In this research, we will present the study of modified dark-current cancellation circuit. The sensing photo-current from 1nA to 10nA of long-wave infrared signal, mid-wave infrared photo-current is about 100pA to 1nA, the dark current is set up to 100nA. The area of unit pixel is 30×30μm² . The 8×6 focal-plane array is designed by using TSMC 0.35μm 2P4M CMOS process. This work has 3.3V power supply and readouts data at 2.5MHz clock rate. The simulated output voltage range of LWIR and MWIR photo-current are 0.95v and 0.76v, respectively.

Quantum well infrared photodetectors (QWIPs) have demonstrated applications in many different areas, such as medical and biological imaging, environmental and chemical monitoring, and infrared imaging for space and night vision. However, QWIPs still suffer from low quantum efficiency and detectivity compared with mercury cadmium telluride (MCT) based interband photodetectors, which dominate current infrared detector market. Besides, n-type QWIPs cannot detect the normal incident infrared radiations because of the polarization selection rules of intersubband transitions. Here, we used periodic holes array perforated in gold film to convert normal-incident infrared light to surface plasmon waves, which can excite the intersubband transitions and be absorbed by quantum wells (QWs). Our 3D FDTD simulation results show that electric field component in the QWs growth direction can be enhanced by more than 5 times compared with the total electric field intensity without any plasmonic arrays. The experimental results show that the photodetector has a peak detection wavelength at ~8 μm with a high detectivity of ~7.4×1010 Jones, and the photocurrent spectrum was very close to the simulation result of the electric field enhancement spectrum.

Research into III-Nitride based avalanche photodiodes (APDs) is motivated by the need for high sensitivity ultraviolet (UV) detectors in numerous civilian and military applications. By designing III-Nitride photodetectors that utilize low-noise impact ionization high internal gain can be realized-GaN APDs operating in Geiger mode can achieve gains exceeding 1×10⁷. Thus with careful design, it becomes possible to count photons at the single photon level. In this paper we review the current state of the art in III-Nitride visible-blind APDs and discuss the critical design choices necessary to achieve high performance Geiger mode devices. Other major technical issues associated with the realization of visible-blind Geiger mode APDs are also discussed in detail and future prospects for improving upon the performance of these devices are outlined. The photon detection efficiency, dark count rate, and spectral response of or most recent Geiger-mode GaN APDs on free-standing GaN substrates are studied under low photon fluxes, with single photon detection capabilities being demonstrated. We also present our latest results regarding linear mode gain uniformity: the study of gain uniformity helps reveal the spatial origins of gain so that we can better understand the role of defects.

We report on the architectural design and fabrication of medium and large arrays of single-photon avalanche diodes (SPADs) for a variety of applications in physics, medicine, and the life sciences. Due to dynamic nature of SPADs, designs featuring a large number of SPADs require careful analysis of the target application for an optimal use of silicon real estate and of limited readout bandwidth. This paper describes the main trade-offs involved in architecting such chips and the solutions adopted with focus on scalability and miniaturization.

A compact readout circuit that can be integrated between individual single photon avalanche detectors (SPADs) is described. The circuit uses minimum sized transistors to both quench the avalanche process in the photodetector and integrate charge onto a capacitor to represent the number of detected photons. An additional transistor is integrated within the circuit so that the integration capacitance can be isolated from the source-follower output circuit before the integration time has elapsed. This device can be used by the user to control the relationship between the number of detected photons and the output voltage.

A single-photon avalanche diode (SPAD) fabricated in a 90nm standard CMOS process is reported. The detector comprises an octagonal multiplication region and a guard ring to prevent premature edge breakdown using exclusively standard layers. The proposed structure is the result of a systematic study aimed at miniaturization, while optimizing overall performance. The device exhibits a dark count rate of 16 kHz at room temperature, a maximum photon detection probability of 16% and the jitter of 398ps at a wavelength of 637nm. Applications include time-of-flight 3D vision, fluorescence lifetime imaging microscopy, fluorescence correlation spectroscopy, and time-resolved gamma/X-ray imaging. Standard characterization of the SPAD was performed in different bias voltages and temperatures.

In the last years the fabrication of SPAD cameras has become one of the main fields of interest in 3-D imaging and bioapplications. In this paper we present the comparison between two standard CMOS technologies to fabricate SPADs cameras. The two technologies used in the comparison are a high voltage 0.35μm technology from AMS and a high integration 130nm technology from STM. The advantage of using a standard CMOS technology among a dedicated is the possibility of integrating the control/reading electronics into the same die. Neither of the processes is optimized for optical applications, and no post-processing has been applied to improve the features. The technologies have been selected due to the different integration density, and different intrinsic process parameters with similar cost. Comparison has been done by fabricating several structures in both technologies which allow analyzing sensibility, noise, and time response. Experimental results show that the high voltage technology has a lower level of dark counts than the 130nm. Instead, the high integration technology has a shorter quenching time, 1.5ns, which reduces the afterpulsing events to a negligible level. In optical applications it is important to have a high integration of the camera reducing the pitch of the pixel, while noise effects can be corrected in post-processing. For low frequency events, such as high energetic particle tracking, the noise frequency has to be lower, but it is also required a high fill factor. Depending on the specific application this analysis allows to opt for the most suitable technology.

Imaging techniques based on time-correlated single photon counting (TCSPC), such as fluorescence lifetime imaging microscopy (FLIM), rely on fast single-photon detectors as well as timing electronics in the form of time-to-digital or time-to-analog converters. Conventional systems rely on stand-alone or small arrays (up to 32) of detectors and external timing and memory modules. We recently developed a fully integrated image sensor containing 32×32 pixels and fabricated in a 130 nm CMOS technology. The chip produces an overall data rate of 10Gb/s in terms of time-of-arrival measurements in each pixel. As opposed to conventional single detector FLIM systems, the present system can acquire a full image, albeit at low resolution, without the need of an optical scanning system. As a consequence the complexity of the optical setup is reduced and the acquisition speed is dramatically increased. We show the potential of this new technology by presenting high time resolution (119 ps) TCSPC-FLIM images of pollen grains with acquisition times as low as 69 ms. Furthermore, the low noise (~100 Hz) and high photon detection probability (up to 35%) ensure a good photon economy over the visible spectrum. We believe that this technology will open the way to fast TCSPC-FLIM recordings of transient signals in the bio- and life sciences, such as in neuron signaling.

Active, three-dimensional long-range imaging has varied applications in a number of disciplines, including manufacturing, environmental sensing and defence. Common constraints often include low average and peak illumination powers to ensure eye-safety, making the potentially high sensitivity of the single-photon counting technique a distinct advantage. We present a scanning time-of-flight imager based on high repetition-rate (>MHz) pulsed illumination and a silicon single-photon detector. In advanced photon-counting experiments, we recently employed the system for unambiguous range resolution at several kilometres target distance, multiple-surface resolution based on adaptive algorithms, and a cumulative data acquisition method that facilitates detector characterisation and evaluation. This article reviews these achievements and identifies multi-spectral imaging as a possible future application.

Photon-counting detectors are required for numerous NASA future space-based applications including science instruments and free-space optical communication terminals. We discuss the baseline and alternative photon counting detectors that are under evaluation for deployment on the Ice, Cloud and land Elevation Satellite-2 (ICESat2) Advance Topographic Laser Altimeter System (ATLAS). Future NASA science instruments and free space laser communication terminal receiver performance can be improved by using single-photon-sensitive detectors. Photomultipliers and avalanche photodiodes are the primary candidates. Single-photon-sensitive detectors provide efficient receivers that minimize the required space-based resources (size, weight, power and cost).

×We describe the design, fabrication, and performance of focal plane arrays (FPAs) for use in 3-D LADAR imaging applications requiring single photon sensitivity. These 32 × 32 FPAs provide high-efficiency single photon sensitivity for three-dimensional LADAR imaging applications at 1064 nm. Our GmAPD arrays are designed using a planarpassivated avalanche photodiode device platform with buried p-n junctions that has demonstrated excellent performance uniformity, operational stability, and long-term reliability. The core of the FPA is a chip stack formed by hybridizing the GmAPD photodiode array to a custom CMOS read-out integrated circuit (ROIC) and attaching a precision-aligned GaP microlens array (MLA) to the back-illuminated detector array. Each ROIC pixel includes an active quenching circuit governing Geiger-mode operation of the corresponding avalanche photodiode pixel as well as a pseudo-random counter to capture per-pixel time-of-flight timestamps in each frame. The FPA has been designed to operate at frame rates as high as 186 kHz for 2 μs range gates. Effective single photon detection efficiencies as high as 40% (including all optical transmission and MLA losses) are achieved for dark count rates below 20 kHz. For these planar-geometry diffused-junction GmAPDs, isolation trenches are used to reduce crosstalk due to hot carrier luminescence effects during avalanche events, and we present details of the crosstalk performance for different operating conditions. Direct measurement of temporal probability distribution functions due to cumulative timing uncertainties of the GmAPDs and ROIC circuitry has demonstrated a FWHM timing jitter as low as 265 ps (standard deviation is ~100 ps).

We present our latest results from a novel nano-injector-base photon detector. Previously, we have demonstrated the excellent noise performance and large linear gain of single-element devices at room temperature. Here we demonstrate the first focal plane array (FPA) made from this unique device, and show that they hold their high gain and low noise performance at a good array uniformity. The high internal gain produces significantly better images at high frame rates, or at low light level conditions.

There is a need for semiconductor-based ultraviolet photodetectors to support avalanche gain in order to realize better performance andmore effective compete with existing technologies. Wide bandgap III-Nitride semiconductors are the promising material system for the development of avalanche photodiodes (APDs) that could be a viable alternative to current bulky UV detectors such as photomultiplier tubes. In this paper, we review the current state-of-the-art in IIINitride visible-blind APDs, and present our latest results on GaN APDs grown on both conventional sapphire and low dislocation density free-standing c- and m-plane GaN substrates. Leakage current, gain, and single photon detection efficiency (SPDE) of these APDs were compared. The spectral response and Geiger-mode photon counting performance of UV APDs are studied under low photon fluxes, with single photon detection capabilities as much as 30% being demonstrated in smaller devices. Geiger-mode operation conditions are optimized for enhanced SPDE.

We map the transverse profile of light beams using photon-number-resolving detectors, and observe compression of beam profiles for higher detected photon-number. This compression is exploited to enable contrast enhancement between two point images separated at the Rayleigh limit. This enhancement exists for all separations up until the classical Sparrow limit.