After an introductory section on pulse tube cryocoolers (PTC) this paper reports the state of development of some medium-size PTCs for potential future replacement of commercial Stirling cold fingers. The coolers were designed for operation with the AIM SL200 compressor (nominal input power: 100 W) and Leybold Polar SC7 compressor (nominal input power: 200 W), respectively. Adjustment of phase shift between pressure and mass flow oscillation is accomplished by means of inertance tubes in combination with a reservoir and a second-inlet flow impedance that are attached to the warm end of the pulse tube. Two coolers with U-shaped and one with linear arrangement of regenerator and pulse tube have been built and optimized. Up to now, the smaller U-shaped PTC driven by the AIM compressor at 100 W input power reached a no-load temperature of 45 K, and a cooling capacity of 2.85 W at 80 K is achieved, corresponding to a coefficient of performance of COP = 2.85 %. For the two larger PTCs driven by the Leybold compressor at 200 W of input, the obtained no-load temperature and cooling power at 80 K are 38 K and 6 W for the U-shaped cooler and 44 K and 8.1 W for the linear cooler, corresponding to COPs of 3 % and 4 % at 80 K, respectively. Measurements of the refrigeration temperature as function of the cold head orientation with respect to gravity revealed a small convection-induced temperature variation of several percent. The minimum temperature is achieved with the pulse tube cold end facing downwards.

Flexure spring suspensions have demonstrated the capability of extending cryocooler lifetimes for space-based and commercial cryocooler applications. In the mid-1990s DRS Infrared Technologies, L.P. began an effort to adapt this technology to cryocoolers for tactical sensor applications. The flexure spring suspension system resulting from that effort has been described in previous papers. The flexure spring designs met the various size, weight, performance, and implementation requirements. This paper presents an update of the environmental and life testing that has been done to qualify these designs for military sensor applications.

The life time tests realised on the serial production of Rotary Mmonoblock RM2 coolers show a measured MTTF of 4900 hours. The conventional test profile applied to these coolers is representative of operation in typical application. The duration of such life time tests is very long. The results of a design change and its impact on MTTF are available only several months after the assembly of the prototypes. We decided to develop a test method in order to reduce the duration of these life time tests. The principle is to define a test protocol easy to implement, more severe than typical application profile in order to accelerate life time tests. The accelerated test profile was defined and tested successfully. This new technique allows us to reduce life time tests costs and duration and thus the costs involved. As a consequence, we decided to have a screening of our production with this accelerated test. This allows us to master continuously the quality of our serial products and to collect additional data. This paper presents the results of life time tests performed on RM2 coolers according to the conventional and accelerated test profiles as well as the first results on the new RM2 design which show a calculated MTTF of 10000 hours.

The Standard Advanced Dewar Assembly (SADA) is the critical module in the Department of Defense (DoD) standardization effort of scanning second-generation thermal imaging systems. DoD has established a family of SADA's to address requirements for high performance (SADA I), mid-to-high performance (SADA II), and compact class (SADA III) systems. SADA's consist of the Infrared Focal Plane Array (IRFPA), Dewar, Command and Control Electronics (C&CE), and the cryogenic cooler. SADA's are used in weapons systems such as Comanche and Apache helicopters, the M1 Abrams Tank, the M2 Bradley Fighting Vehicle, the Line of Sight Antitank (LOSAT) system, the Improved Target Acquisition System (ITAS), and Javelin's Command Launch Unit (CLU). DOD has defined a family of tactical linear drive coolers in support of the family of SADA's. The Stirling linear drive cryo-coolers are utilized to cool the SADA's Infrared Focal Plane Arrays (IRFPAs) to their operating cryogenic temperatures. These linear drive coolers are required to meet strict cool-down time requirements along with lower vibration output, lower audible noise, and higher reliability than currently fielded rotary coolers. This paper will (1) outline the characteristics of each cooler, (2) present the status and results of qualification tests, and (3) present the status and test results of efforts to increase linear drive cooler reliability.

The demand for more cooling power for infrared imagers, which may require up to 3 W of cooling power at 77 K, is nowadays surpassed as other industries are getting interested in cryogenic cooling as well. These potential markets require robust, efficient and affordable coolers with cooling capacities in excess of 6 W. As announced at the previous SPIE conference in 2000, Thales Cryogenics has been working on the development of a cryocooler based on the LSF 918x series consisting of a flexure bearing compressor in combination with a 20 mm Stirling cold finger in order to meet the demands of this emerging markets. Based on the proven principles of Thales LSF 91xx flexure bearing compressors, a moving magnet compressor was designed that delivers the required pressure wave for this larger cold finger. The compressor has been successfully tested in combination with the 20 mm cold finger resulting in the LSF 93xx cooler. For the second half of 2002, tests are planned for the combination of a version of this compressor with a 5 W pulse tube cold finger. At present, the European Space Agency is funding the space qualification of a modification the LSF 93xx cooler, in order to use it to provide the cryogenic cooling required for future manned missions. A test program for the specific requirements for the CRYOSYSTEM program is under progress. This paper describes the trade-offs that have been considered in the design phase, and gives a detailed overview of the test results and the resulting specification of the LSF 93xx coolers.

Advanced Split Linear and Integral Stirling cryocoolers for IR applications are controlled by external or integrated control electronics to provide a stable preset temperature at the focal plane. AIM produces a family of Split Linear Stirling coolers with integrated control electronics inside the compressor housing. The new AM 7 electronic is standardized to one configuration which meets the different input power requirements and temperature settings of all AIM coolers ranging between 10W to 105W input power. AIM has completed the development of the AM 7 electronics to improve temperature stability over the entire range of operating conditions and to optimize ramp up of input power for different cool down conditions. Thus, reduced cooldown time at high ambients and softer startup at low temperatures are achieved. Optionally, the electronics can be supplemented with an external add-on microprocessor unit for advanced system requirements. The 3rd generation electronics will be implemented into rate production 4Q2002.

We report on the development of methods and equipment which facilitates the measurement of the Modulation Transfer Function (MTF) of IR optics exposed to both high and low temperatures. The MTF is a very powerful measure of the quality of any optical system, and is a common way to test the performance. However, because of the large apparatus needed to perform the testing it is generally not possible to measure the MTF at temperatures other than room temperature. A thermally insulating enclosure was designed in which the optics under test is placed on a temperature-controlled fixture. The enclosure permits the radiation to reach the optics under test and allows the MTF measurement probe to reach the image plane. Meanwhile the MTF measurement bench is kept at room temperature. In this way it is possible to vary the temperature of the optics under test between -30 °C and +85 °C and simultaneously measure the MTF. Using the same equipment it is also possible to measure bore sight error, ensquared energy, and focus position as a function of temperature. A commercially available MTF measurement bench was specially adapted for this purpose. Measurements can be made both on- and off axis and both MWIR and LWIR measurements are possible.

Saab Bofors Dynamics has developed an IRST-system (Infra Red Search and Track) named IR-OTIS (Optical Tracking and Identification System) and flight trials have been carried out with the system mounted on a Saab JA37 Viggen fighter aircraft. This paper consists of three major parts. First an overview of Saab's IRST-programs. The second part describes the system ( IR-OTIS(Viggen) ) that made flight trials during 1998 and 1999 and finally a report from the flight trials. IR-OTIS has mainly three operating modes: 1) IRST-mode where the system covers several different FOS (Field Of Search). 2) FLIR-mode (Forward Looking IR) where the systems LOS (Line Of Sight) is directed from the aircraft. 3) Track-mode where the built-in-tracker controls the LOS. It is also possible to switch from IRST-mode to track-mode automatically. Physically the IR-OTIS(Viggen) consists of the SU (Sensor Unit) and the SPU (Signal Processing Unit). The SU is operating in the longwave IR-band with a 288*4 detector. In all modes the Sensor Unit generates images in 25 Hz and it is also possible to choose one of three FOV. The SPU consists of a Saab designed image processing hardware and several DSPs. Functions in the SPU includes a scene-based NUC (Non Uniformity Correction), anti-Narcissus, a point-target detector including estimation of SNR and a clutter classifier for CFAR, target association, a correlation target tracker and an AGC for image presentation. We carried out over 50 flight trials during 1998 and 1999 in three different rounds. The functionality of the system has increased during the rounds and at the end of the trials all major goals were achieved.

A method for calculation of the target range of an airborne IRST has been verified with data from flight trials. The calculation method includes modelling of sensor performance, atmospheric transmission and infrared radiation from target and background. The flight trials were performed with the IR-OTIS system mounted on a Saab JA37 Viggen fighter aircraft, and a similar aircraft serving as target. Detection range was measured at various flight altitudes, for front and rear aspect. The correspondence between measured and predicted range is very good, with a deviation of less than 10 %.

This paper presents the main actors in the Finnish infrared research community in the Defense Forces, the civilian research institutes and industry. Within the Defence Forces, the Defence Forces Research Centre (PvTT) has a key role as the most important research institute dealing with military technology in Finland and as an integrator of civilian expertise. The basic research strategy of the Finnish Defense Forces is to rely on external research institutes (either domestic or foreign) and to concentrate its own resources only on the areas where external expertise is not available. Accordingly, the research focus of PvTT is on the signature research and the environmental conditions affecting the performance of infrared sensors. The paper also describes the work done at the Technical Research Centre of Finland (VTT) and at various universities. The role of the Finnish defense industry has been fairly modest, but both its own products and recent technology transfer agreements may change the situation in the long run.

Infrared technology in Norway started at the Norwegian Defense Research Establishment (FFI) in the 1960s, and has since then spread to universities, other research institutes and industry. FFI has a large, integrated IR activity that includes research and development in IR detectors, optics design, optical coatings, advanced dewar design, modelling/simulation of IR scenes, and image analysis. Part of the integrated activity is a laboratory for more basic research in materials science and semiconductor physics, in which thin films of CdHgTe are grown by molecular beam epitaxy and processed into IR detectors by various techniques. FFI also has a lot of experience in research and development of tunable infrared lasers for various applications. Norwegian industrial activities include production of infrared homing anti-ship missiles, laser rangefinders, various infrared gas sensors, hyperspectral cameras, and fiberoptic sensor systems for structural health monitoring and offshore oil well diagnostics.

Acreo in Sweden has been invovled in Quantum Well IR Photodetector (QWIP) reserach and development since 1986. During the first years a small group led by Jan Andersson was dedicated to research on QWIP structures and means of coupling radiation into the quantum-well structure. One of the resarech results is a 2D optical grating couler to create an optimal elecgtric field pattern for highest possible absorption and responsivity. Acreo holds a patent for this grating coupler. Since 1988 FLIR Systems, later FMV, Saab Dynamics, Celsius Tech and NUTEK have sponsoered an R and D project with the goal to develop QWIP detectors and start up production. Soon it became clear that an adapted ROIC deisng and the hybridization of the focal plane array are key issues in order to achieve the highest possible performance and operability of the complete detector device for voluem production. Extended measures where taken in 1996. In 1997 the industrial interest increased further, ClesiusTech and Saab Dynamics, merged in 2000, and now a division of FLIR Systems AB started to sponsor the R and D project. Because of its success during the last years it has now been expanded and scheduled until 2003 and beyond. Volume production of QWIP FPAs started in 2000.

Multispectral data in the mid-wave spectral region can provide significant information for the characterization of both manmade objects and natural background. Processing multi-spectral images is still in its infancy, complicated by the fact that spectral characteristics change from place to place in the scene. A multispectral high performance imaging sensor for the spectral region 1.5 - 5.2 µm has been specified and obtained from AEG INFRAROT-MODULE GmbH. The instrument is equipped with a spinning filter wheel containing four filters closely related to the atmospheric windows. The spectral bands are also selected to distinguish between reflected and emitted radiation and also to distinguish between targets of different temperature and emissivity. The full frame rate is 100 Hz, and up to 800 Hz is possible using sub-windowing. Applications include missile warning, reconnaissance, surveillance, tracking and identification.

The Swedish Army is currently taking serial deliveries of a QWIP-based thermal imaging sight for anti-tank missiles. Two other applications of QWIP imagers are being evaluated for near time acquisition by the Swedish and Norwegian armies. This paper gives an overview of these programs and their background. Experience has been gained during field trials of these instruments, and highlights advantages and problems of this new technology and their solutions. One example is the low NETD of these imagers, which, while being a great advantage, also presents entirely new problems compared to older technologies. Reasons for the choice of QWIP technology for these programs are discussed. QWIP based thermal imagers are gaining ground in military applications and the Scandinavian countries are the early adopters

Negative luminescent (NL) devices, which to an IR observer appear colder than they actually are, have a wide range of possible applications, including for use as IR sources in gas sensing systems and as thermal radiation shields in IR cameras. Additionally these devices can be used as calibration sources for very large IR focal plane arrays and have many potential advantages over conventional calibration sources, including high speed operation and low power consumption. For many of these applications a large area device which displays as large area device which displays as large as possible apparent temperature range is required. However, under reverse bias significant currents are required to reduce the carrier concentrations to the levels needed for maximum dynamic range. We have therefore used a novel micromachining techniqe to fabricate integrated optical concentrators in InSb/InAlSb and HgCdTe NL devices. Smaller area diodes can then be used to achieve the same absorption and the required currents are thus reduced. To fabricate the concentrators, spherical resist masks are first produced by resist reflow. Inductively coupled plasma etchign is then used to alternatley etch the resist mask and the semiconductor, with oxygen and methane/hydrogen respectively, producing concentrators with almost parabolic profiles. Recent results from large area medium wavelength devices with integrated optical concentrators are presented, together with a description of the continuing optimization of the process and progress towards the fabrication of large area long wavelength devices.

A key issue for face recognition has been accurate identification under variable illumination conditions. Conventional video cameras sense reflected light so that image gray values are a product of both intrinsic skin reflectivity and external incident illumination, obfuscating intrinsic reflectivity of skin. It has been qualitatively observed that thermal imagery of human faces is invariant to changes in indoor and outdoor illumination, although there never has been any rigorous quantitative analysis to confirm this assertion published in the open literature. Given the significant potential improvement to the performance of face recognition algorithms using thermal IR imagery, it is important ot quantify observed illumination invariance and to establish a solid physical basis for this phenomenon. Image measurements are presented from two of the primarily used spectral regions for thermal IR; 3-5 micron MidWave IR and the 8-14 micron LWIR. All image measurements are made with respect to precise blackbody ground-truth. Radiometric calibration procedures for two different kinds of thermal IR sensors are presented and are emphasized as being an integral part to data collection protocols and face recognition algorithms.

To explore the feasibility of utilizing an IR imaging system to support flow visualization studies, an initial series of tests were conducted using an AN/AAS-38, NITE Hawk targeting pod. The targeting pod, installed on the left side of an F/A-18 aircraft provides a stabilized infrared imaging capability in the 8-12 micron spectral band. Initial data acquired with system indicated that IR thermography was a very promising tool for flow visualization. For the next phase of the investigation, an advanced version of the NITE Hawk targeting pod equipped with a staring 3-5 micron sensor was utilized. Experimental results obtained with this sensor indicated improved sensitivity and resolution. This method was limited to position the experiment and chase aircraft sufficiently close to each other and with the sightline angle required to acquire the region of interest. For the current phase of the investigation, the proven 3-5 micron staring sensor was deployed in an externally mounted podlet, located on the experimental aircraft with a fixed line of sight, centered on the region of interest. Based on initial data collection efforts, this approach appears to provide consistent high quality data for a wide range of flight conditions. To minimize the size of the podlet and resultant drag, the sensor was oriented parallel to the air flow. This also placed the line of sight parallel to the experiment. A fold mirror was incorporated in the design to fold the line of sight inboard and down to center on the region of interest. The experimental results obtained during the current test phase have provided consistently high quality images clearly mapping regions of laminar and turbulent flow. Several examples of these images and further details of the experimental approach are presented.

An uncooled infrared (IR) imaging system based on thermomechanical deformation of bi-material cantilever beams combined with optical detection of beam deflection has been developed. The focal plane array (FPA) contains 300 x 300 cantilever sensors, which are optimized to detect IR radiation in the 8-14 μm wavelength range. Noise and response analysis show that the noise-equivalent temperature difference (NETD) of the system is 200 mK using f/1 IR optics and 10 Hz frame capture rate. The NETD is found to be limited by the shot noise of the visible CCD imager used in the optical readout. Statistical correlation between two repeated tests separated by 10 minutes shows that the response of over 70 percent pixels are repeatable to within 60 percent.

DRS has been conducting several significant ongoing efforts to improve the producibility of its uncooled IR focal plane products. Those efforts are described in this paper. First, pixel dimensions are being reduced by a factor of two or mroe, while maintaining NETD performance levels fully comparable to that of the previous standard approximately 50-micron pixel size. The results for a given array size is smaller die size and mroe die per wafer. Second, DRS is transitioning UIRFPA production from its 5-inch wafer diameter process facility in Anaheim, CA to its 6-inch wafer diameter process facility in Dallas, TX, which results in more die per wafer and in enhanced wafer throughput capacity. Furthermore, the Dallas UFPA production facility is being tooled for a smooth future transition to 8-inch wafer processing. Third, a new ceramic UIRFPA vacuum package has been developed, which has lower material cost, fewer parts and assembly operations, and is lighter significantly weight than the current standard metal package. Since packaging is inherently the most expensive part of UIRFPA manufacture, packaging producibility improvements can provide significant cost leverage. Fourth, DRS is developing a batch-mode UIRFPA vacuum bake and sealign system, which will achieve significant throughput capacity gains, reduce touch labor requirements, and reduce production cycle times.

In a previous paper to the present forum we outlined the Infrared Components Corporation (ICC) microbolometer development program based on technology licensed from the Australian Defence Science and Technology Organisation (DSTO). We presented an overview of the processing technology and discussed the technology transfer package being developed for implementation in a silicon MEMS foundry. In this paper the progress of the program will be reported, including work at DSTO and Electro-optic Sensor Design (EOSD), and technology transfer to the 200mm MEMS foundry at the SUNY Albany Institute of Materials (UAIM). The development of a new readout integrated circuit (ROIC) and associated camera initiatives at ICC will be discussed.

Spectral responsivity of an uncooled IRFPA with SOI diode detectors has been measured using a free electron laser (FEL), which is a new optical source with tunable wavelegnth. Light from the FEL has a complicated pulse structure, and the beam has spatial non-uniformity. These features make it difficult to evaluate the responsivity of the thermal detector with the FEL. To measure the responsivity, images of the FEL beam are recorded and analyzed by an image processor. The spectral resonsivity obtained is flat in the wavelength from 5μm to 16.5μm, and the effect of the optical resonant is smaller than that of a two-level microbolometer.

Raytheon IR Operations (RIO) has achieved a significant technical breakthrough in uncooled FPAs by reducing the pixel size by a factor of two while maintaining state-of-the-art sensitivity. Raytheon has produced the first high-quality 320×240 microbolometer FPAs wiht 25μm pitch pixels. The 320×240 FPAs have a sensitivity that is comparable to microbolometer FPAs with 50μm pixels. The average NETD value for these FPAs is about 35 mK with an f/1 aperture and oepratin at 30 Hz frame rates. Good pixel operability and excellent image quality have been demonstrated. Pixel operability is greater than 99 percent on some FPAs, and uncorrected responsivity nonconformity is less than 4%. The microbolometer detectors also have a relatively fast thermal time constant of approximately 10 msec. This state-of-the-art performance has been acheived as a result of an advanced micromachining fabrication process. The process allwos maximization of both the thermal isolation and the optical fill-factor. The reduction in pixel size offers several potential benefits for IR systems. For a given system resolution requirement, the 25 μm pixels allow a factor of two reduction in both the focal length and aperture size of the sensor optics. The pixel size reduction facilitates a significant FPA cost reduction since the number of die printed on a wafer can be increased. The pixel size reduction has enabled the development of a large-format 640×480 FPA array. Raytheon has produced arrays with very good sensitivity, operability, and excellent image quality. These FPAs are applicable to wide-field-of-view, long range surveillance and targeting missions. Raytheon is also developing a high performance 160×128 FPA that is designed for applications where miniaturizaitno and temperature invariance are required as well as low cost and low power.

After the development of an amorphous silicon based uncooled microbolometer technology, LETI and ULIS are now working to facilitate the IR focal plane arrays (IRFPA) integration into equipment in order to address a very large market. Achievement of this goal needs the integration of advanced functions on the focal plane and the decrease of manufacturing cost of IRFPA by decreasing the pixel pitch and simplifying the vacuum package. We present in this paper the new designs for readout circuit and packages which will be used for 320×240 and 160×120 arrays with a pitch of 35μm.

An Oxide over Titanium metal resistance bolometer technology developed by NMRC (Ireland) has been transferred to the X-FAB UK CMOS foundry at Plymouth, UK. Prototypes of the bolometers have been manufactured in the X-FAB production facility and tests show performance comparable with the NMRC prototypes. The bolometer design has been integrated with a CMOS read-out chip and the first wafers are currently being packaged for evaluation. The development of a low cost thermal imaging camera using the detector is under way. We present an overview of the detector and camera design, together with preliminary results from the detector test programme. The work is partly funded by the European Union IST programme.

This paper presents the first-ever 120×90 element thermoelectric IR focal plane array (FPA) fabricated wiht CMOS technology. The device has a high repsonsivity of 3,900 V/W and a low cost potential. The overall chip size is 14.4 mm × 11.0 mm with a 12.0 mm × 9.0 mm imaging area. The device structure was optimzed for a vacuum-sealed package. Each detector consists of two pairs of p-n polysilicon thermocouples and an NMOS transistor and has external dimensions of 100μm x 100μm and an internal electrical resistance of 90kΩ. The precisely patterned Au-black IR absorbing layer was achieved by both a low-pressure vapor deposition technique and a lift-off technique utilizing a PSG sacrificial layer. These techniques make it possible to obtain a Au-black pattern with the same degree of accuracy as with the CMOS process. The Au-black layer showed high absorpitivty of more than 90 percent to the light source with a wavelength of from 8 to 13μm. This performance is suitable for consumer electronics as well as automotive applications.

Liquid-nitrogen cooled quantum-well infrared photodetectors (QWIP) provide high response and high-speed detection of 10-micron radiation. When processed with high doping, QWIP's have been found to provide sensitive detection for long-wavelength infrared radiation at elevated temperatures. Experimental measurements using both direct and heterodyne detection show excellent performance at 10 microns and at temperatures up to 300 degrees-Kelvin. This high temperature operation allows applications in small or power limited platforms and significantly reduces the cost of the infrared detection system. Although only single element detectors have been evaluated, linear and 2-D arrays are expected to have similar performance characteristics. Experimental results for both video and heterodyne detection will be presented.

A design for an optical seeker optimized for spin-stabilized projectiles is presented. Using the spin of the bullet to scan a linear photodetector array across the target field, a relatively wide field-of-regard seeker may be constructed with an adequate SNR for homing applications. The linear photodetector array is based on room-temperature quantum-well infrared photodetectors (QWIP) optimized for a wavelength of 10.6 microns. The entire seeker containing the 1 × 64-element linear photodetector array, amplifiers and signal processor/flight computer can be constructed on a single 1-cm square bonded chip-on-chip. A compact folded telescope has been designed to collect light from a CO₂ laser designator to guide the projectile to the target. Details of the seeker design as well as laboratory measurements of the concept using a visible light prototype seeker will be presented.

An optimally designed GaAs/AlGaAs broadband Quantum Well IR Photodetector QWIP Focal Plane Array FPA is fabricated and hybridized to a 640 × 512 Read Out Integrated Circuit with 25μm pixel pitch. The substrate-thinned and LCC mounted FPA was loaded into a dewar and cooled to liquid Neon temperature for characterization. The temperature of the FPA was stabilized at 35K several minutes after power was applied. We will report on the NEΔT, QE, uniformity, and D* result.

This paper reports recent results from a novel approach for fabricating RI detectors from GaAs/AlGaAs multiple quantum well (MQW) materials. It involves the fabrication of quantum-well IR photodetectors (QWIPs) by patterning a 3D diffractive resonant optical cavity into the MQW structure. This approach, called the Enhanced QWIP (EQWIP), enables highly effective optical coupling into the MQW material resulting in narrow spectral response, improved detector quantum efficiency (QE), reduced dark currents, and improved photoconductive gain. EQWIP arrays operating in the 8-10 μm spectral band are reported in this paper. The peak response wavelength of the detectors, within the absorption band of the MQW material, is tuned by controlling the dimensions of the resonant structure. EQWIPs with peak spectral response at 8.6 μm exhibit peak responsivity as high as 2.6 A/W and quantum efficiency (QE) as high as 57%. Total conversion efficiency is as high as 35%. The background limited, peak detectivity measured at 9.0μm and 55 K with a 295 K background at f/2.5 is greater than or equal to 1 × 10¹¹ cm-Hz^0.5/W.

We investigated GaAs/AlGaAs QWIP devices that had TiW/Au reflector electrodes and found that the thermal stability, and as a result, the uniformity of the IV characteristics were dramatically improved by the insertion of a TiW diffusion barrier. A secondary ion mass spectroscopy analysis showed that with the TiW insertion, the Au in-diffusion during the thermal process at around 400°C was completely suppressed. A reflectivity measurement of the GaAs/Au and GaAs/TiW/Au structures revealed that the reflectivities were almost the same, indicating the TiW/Au structure was a good candidate for use as a reflector electrode. A comparison of the fabricated GaAs/AlGaAs QWIP devices that had conventional Au with our new TiW/Au reflector electrodes showed that our devices exhibits a performance comparable with that of the conventional devices because of their similar reflectivity. Furthermore, the uniformity of the IV characteristics of more than 50 devices was greatly improved, especially in the reverse-biased region where the upper AlGaAs barrier (nearest to the reflector) served as an electron-emitter.

We report on our QWIP focal plane array (FPA) developments for the 8 - 12 μm and 3 - 5 μm regimes. In the long-wavelength infrared, we have realized several types of QWIP FPAs with array sizes from 256 × 256 to 640 × 512 pixels and with different active regions, giving rise to photoconductive and photovoltaic operation, respectively. Best thermal resolution in the 8 - 12 μm regime is obtained with low-noise QWIP FPAs which are based on a photovoltaic QWIP structure. Special emphasis is given to our work on a 640 × 512 mid-wave QWIP FPA, which is based on strained InGaAs/AlGaAs quantum wells lattice matched to a GaAs substrate. By optimizing the carrier concentration and the geometry of the two-dimensional grating with 1.65 μm period, a high quantum efficiency of more than 10% in the long-wavelength part of the 3 - 5 µm regime is achieved, resulting in an excellent thermal resolution of only 14.3 mK.

A 9 μm cutoff 640×512 pixel hand-held quantum well IR photodetector (QWIP) camera has been demonstrated wiht excellent imagery. Based on the single pixel test data, a nose equivalent differential temperature (NETD) of 8 mK is expected at 65K operating temperature with f/2 optics at 300K background. This focal plane array has shown backgeround lmiited performance at 72K operating temperature with the same optics and background conditions. In this paper, we discuss the development of this very sensitive long wavelength IR (LWIR) camera based on a GaAs/AlGaAs QWIP focal plane array and its performance in quantum efficiency, NETD, uniformity, and operability.

Nova Research, Inc. has developed a novel two-dimensional imaging chip whose design is based on properties exhibited by biological retinas. The 'Variable Acuity' imager permits the user to program a unique spatial arrangement of 'superpixels' that may be updated in real time. Any spatial configuration of pixels in the imager may be realized by programming the device in a way that permits pixels to share their individually-collected photocharge with any or all neighbors. Single and multiple 'foveal' configurations are possible, and these high spatial resolution regions may be 'flown' around the FPA at the will of the controlling processor. This device was developed through the combined requirements of (a) covering a wide total field of view while (b) retaining the highest possible spatial resolution on the targets of interest while at the same time (c) operating at the highest possible frame rate. Many thousands of frames per second are possible with the prototype imager while maintaining high spatial resolution. The prototype device operates as a visible imager, and Nova is pursuing the transition of this technology into the infrared domain. This paper will concentrate on applications of the technology and will show some imagery collected with the prototype system.

Noise property is a prime consideration in designing readout circuits for IR focal plane arrays. Output stage is frequently a dominant noise source in the readout circuit. From this pont of view, we suggest a new noise reduction circuit, which suppresses the noise bandwidth of the output stage. The Noise Bandwidth Suppression (NBS) circuit, which is a RC filter with bistable bandwidth, reduces dynamically the niose bandwidth with the same operation speed. From experimental results, it is found that the NBS circuit can successfully reduce the read noise. Using NBS and CDS, the output stage noise was down to 168μV_rms at 300K. It is expected that the output stage noise will be reduced to about μV_rms at the operation temperature of 77K and the designed readout circuit can satisfy 95% BLIP condition.

Several approaches for segmenting hyperspectral data and automatically detecting unusual objects in natural scenes are discussed. We demonstrate segmentations of hyperspectral imagery based on of the most significant principal components of the hyperspectral data cube. Several applications of the segmented data are treated. Digital morphological operations can be used to isolate segments that match target criteria. Alternatively, background segments can be used to define background endmembers; pixels that are quantitatively spectrally different from the background can then be designated. Analog morphological operations can then be used for clutter rejection and for the detection of objects of particular size and shape.

In recent years IR detector technology has developed from early short linear arrays. Such devices require high performance signal processing electronics to meet today's thermal imaging requirements for military and para-military applications. This paper describes BAE SYSTEMS Avionics Group's Sensor Integrated Modular Architecture thermal imager which has been developed alongside the group's Eagle 640×512 arrays to provide high performance imaging capability. The electronics architecture also supprots High Definition TV format 2D arrays for future growth capability.

This paper describes how a limited form of black-body-based calibration can be integrated into a recently developed algebraic scene-based algorithm for nonuniformity correction (NUC) in focal-plane arrays. The result of this integration is a scene-based NUC algorithm that is radiometrically accurate. By calibrating only those detectors that are on the array perimeter and relying on the scene-based algorithm to calibrate the interior detectors, using the perimeter detectors as a reference, radiometric accuracy can be achieved without disturbing the functionality of interior array elements. What makes this possible is the fact that the scene-based NUC algorithm used here is algebraic in nature and does not rely on any statistical assumptions on the scene irradiance in the image sequence. The algorithm utilizes knowledge of inter-frame motion to 'lock' the biases of the interior array elements to those on the boundary. Notably, this can be achieved regardless of the spatial diversity in the scene and with, typically, a minimal number of frames in an image sequence. The performance of the technique is demonstrated using real infrared data.

ABSTRACT The Cross-track Infrared Sounder (CrIS) is one of many instruments that comprise the National Polar-orbiting Operational Environmental Satellite System (NPOESS). The CrIS instrument is a Michelson interferometer-based sensor that is sensitive to wavelengths between 3.5 and 16 microns. Three separate Focal Plane Array Assemblies (FPAAs) referred to as the Short Wave Infrared Assembly, the Mid Wave Infrared assembly, and the Long Wave Infrared assembly are used to span the spectral range. The CrIS instrument measures the earth radiance at high spectral resolution using the data to provide pressure, temperature and moisture profiles of the atmosphere. The CrIS instrument will help improve both global and regional predictions of weather patterns, storm tracks, and precipitation. The CrIS program selected photovoltaic (PV) detectors for use in all three spectral bands. PV technology outperforms photoconductive detectors in terms of high sensitivity and linearity. Each FPAA consists of a 3×3 detector-matrix that are used to form 9 fields of view (FOV). Each detector has a 1,000 mm active area diameter and has its own cold preamplifier, warm post amplifier and independent high pass filter. This paper describes the performance for all three assemblies that together form the basis of the CrIS Engineering Development Unit 2 (EDU2) Detector Preamp Module (DPM). Molecular Beam Epitaxy (MBE) is used to grow the appropriate bandgap n-type Hg_1-xCd_xTe on lattice matched CdZnTe. SWIR, MWIR and LWIR 1000 mm diameter detectors have been manufactured using the Lateral Collection Diode (LCD) architecture. Custom pre-amplifiers have been designed to interface with the large SWIR, MWIR and LWIR detectors. The operating temperature is above 78 K, permitting the use of passive radiators in spacecraft to cool the detectors. Recently, all three FPAAs were completed and tested. The tests performed on each assembly are listed.

The National Polar-orbiting Operational Environmental Satellite System (NPOESS) Cross-track Infrared Sounder (CrIS) is a Fourier Transform interferometer-based sensor used to measure earth radiance at high spectral resolution and low spatial resolution. Measured radiance data are analyzed by end users to provide pressure, temperature and moisture profiles of the atmosphere. The CrIS instrument contains Mercury-Cadmium-Telluride (MCT) photovoltaic (PV) detectors with spectral response in the SWIR, MWIR and LWIR ranges. The CrIS instrument requires large area detectors with state-of-the-art detector performance at temperatures attainable with passive cooling. In the case of the LWIR bands noise associated with the detectors limit the instrument performance. In this paper we describe a study of the noise characteristics of a sample of CrIS MCT PV detectors, emphasizing acquisition and validation of 1/f noise measurements for these devices. Interesting aspects of the 1/f noise dependence on bias-voltage and bias-current are noted. The results are analyzed further in a companion paper1 that emphasizes the relationship between leakage current mechanisms in the diodes and 1/f noise observed.

The National Polar-orbiting Operational Environmental Satellite System (NPOESS) Cross-track Infrared Sounder (CrIS) is a Fourier Transform interferometric sensor that measures earth radiances at high spectral resolution. Algorithms use the data to provide pressure, temperature, and moisture profiles of the atmosphere. The CrIS instrument contains photovoltaic detectors with spectral cut-offs denoted by SWIR, MWIR and LWIR. The CrIS instrument requires large-area, photovoltaic detectors with state-of-art detector performance at temperatures attainable with passive cooling. For example, detectors as large as 1 mm in diameter are required. To address these needs, Molecular Beam Epitaxy (MBE) is used to grow the appropriate bandgap n-type Hg_1-xCd_xTe on lattice matched CdZnTe. The p-side is obtained via arsenic implantation followed by appropriate annealing steps.

Medium wavelength IR arrays have been develoepd which have 1024×768 pixels on a 26 micron pitch. The arrays are made from epitaxially grown indium antimonide, the use of which confers two advantages over conventional InSb owing to the ability to exercise atomic level control of dopants and material thicknesses. Firstly, the photodiodes can be grown on degenerately doped InSb substrates which have a high degree of transparency, so the requirement for the substrate to be thinned is much reduce dleading to simplified manufacture. Secondly, it offers the potential for an increase in operating temperature of many tens of degrees, through elimination of contact leakage currents, though we focus on 80K performance here for comparison with conventional structures. We present initail results form arrays which indicate high operability, despite the need to stitch reticles in the fabrication of the silicon read-out circuit, and temperature sensitivity close to the theoretical limit. Imaging from the arrays compares very favorably with that taken using generation II cameras and gives confidence that this technology offers a cost effective route to large format MWIR systems.

Space-based remote sensing instruments used in Earth resource monitoring applications need to provide multispectral (PAN, VNIR, SWIR), wide field of view (WFOV), small ground sample distance (GSD), and high SNR performance. Focal Plane System's used in these applications must provide high sensitivity, small pixel size, and large numbers of cross-scan pixels, in small, light weight, low power hardware configurations that provide simple electrical interfaces. In 1997, Raytheon delivered a MS/PAN FPS as part of NASAs Earth Observing-1 program. This program provided flight validation data for key FPS technologies that are the foundation for today's multispectral, focal plane systems. Since 1997, there have been a multitude of technology advancements which significantly enhance the performance capabilities of today's FPS designs: Hybrid SiPIN and SWIR HgCdTe detector array/CTIA ROIC pixel area reduction; Improved CTIA transimpedance gain, read noise, linearity, electrical power and uniformity performance and Focal Plane Electronics size, weight and power performance improvements.

Sofradir HgCdTe homojunction IR detector technology has already demonstrated its high maturity level by enabling the delivery of more than 7000 second and third generation IR detectors mainly adapted to LWIR and MWIR waveband applications. The candidates for these detectors are the high performance military applications as well as the space applications, and the commercial application. The new challenge for cooled detectors is the cost-effective production of very large staring arrays. The best approach is the pitch reduciotn keeping constant the performance, which allow to reduce the production cost and to offer larger formats using the same cryogenics. Sofradir MCT technology is now mature at production level for 20μm pitch and even less and has demonstrated its ability to operate a thigher temperatures than other competition materials. This reduces the cooling constraints by using smaller and less costly coolers. The new results of 640×512 MWIR arrays with 20μm pitch are presented as well as the tradeoffs for larger aray formats. QWIPs are also a solution for LWIR detectos offered by Sofradir and Thales Research Technology and this unique technology allows Sofradie to offer large staring ararys with reduced cooling constraints thanks to the high operating temperature achieved keeping constant the performance. Thus QWIP detector performances and production are discussed.

Narrow gap IV-VI layers grown epitaxially on Si(111)-substrates by molecular beam epitaxy exhibit high quality despite the large lattice and thermal expansion mismatch. We present the further development of the first realization of a 2-d narrow gap IR-FPA an a Si-substrate containing the active addressing electronics: A 96 × 128 array with 75μm pitch for row-by row electronic scanning and parallel read-out of the line addressed. Each pixel contains a bare Si-area onto which epitaxial growth occurs, and an access transistor. A MWIR PbTe layer is grown by MBE onto completed Si-read-out substrates at temperatures below 450°C. Photovoltaic sensors are then delineated in the layers. Each pixel is connected to the Si read-out by sputtered Al-stripes. The FPA is mounted in a dewar and demonstrational thermal images are taken.

We have developed InGaAs linear arrays for earth remote sensing for a long time. Results from spaceborne detectors have shown unexpected radiation damage: the dark current of some pixels, scattered over the array, increases in a stepwise manner, and the affected pixels randomly oscillate between metastable states. Ground irradiation tests with high energy protons have provided evidence that the damage is located in the InGaAs diodes, and is enhanced by the CCD readout mode, which requires a -1V reverse bias. A detailed analysis of the mechanisms involved is presented, and led to the design of a new readout circuit based on CTIA amplifiers which integrate the photocurrent around zero bias. This new readout mode is much less sensitive to dark current drifts and instabilities, as the dark current is reduced by several orders of magnitude compared to the previous design. Furthermore, the noise level is improved by 30 percent. Besides this basic improvement, the pixel pitch was halved to increase the ground resolution, so that the new array contains 6000 pixels. The performance is described with a particular focus on noise properties. This new array was tested under proton irradiation with negligible effects.

The SWIR subband presents a growing interest for military, commercial and space applications such as non-destructive test, spectrometry, hyperspectral instruments. In addition to the interest of this specific waveband, these detectors present the advantage of a combination of high performance with the use of thermoelectrical cooler for cooled and uncooled applications. Thus, in order to answer the different market needs for these types of applications, Sofradir has developed different IR detectors in the SWIR waveband. Sofradir offers a 2.5μm cut-off operating around 200K, a 2μm cut-off operating at 250K and a 1.6μm cut-off operating at ambient temperature. The main characteristics and performance results are given as well as the main trade-offs achieved for large quantity productions.

Diode structures of short wavelength infrared (SWIR) InGaAs material were grown epitaxially on 3 inch GaAs substrates by molecular beam epitaxy. Despite the large lattice mismatch of 6% between In_0.8Ga_0.2As and GaAs the diode performance allows applications in spectroscopy and imaging. Photovoltaic diode characterization measures like R0A product and quantum efficiency were extracted from I-V curves. The layers are processed with standard photolithography and micro-structuring tools and finally flip-chip bonded on a silicon read out integrated circuit (ROIC). Linear arrays of 256 and 512 pixel with 25 mm pitch were fabricated as well as focal plane arrays (FPA) of 256 × 320 pixel with 30 mm pitch. Functionality is proven by using the assemblies in systems for spectroscopy and beam profiling up to 2.5 mm wavelength.

This paper describes the background to the planned upgrade of the UK Light Armoured Vehicle fleet, focussing specifically on the introduction of Thermal Imaging and Tactical Navigation systems which meet the requirement to conduct 24 hour operations and enhance the situational awareness of the crew. The main bulk of the paper will concentrate on the Battle Group Thermal Imaging (BGTI) system(s) selected by the UK Ministry of Defence (MoD) to be installed on the Warrior Armoured Infantry Fighting Vehicle (AIFV) and Scimitar Close Recce vehicle. In particular the paper will describe the Gunners Sight, the integrated Commanders Crew Station, the Tactical Navigation sub-system and the interfacing of the Thales Optronics BGTI system to the General Dynamics Bowman Radio and Battlefield Management System (BMS). Throughout the paper, the Author will make reference to the need to offer affordable solutions that ensure the total cost to the UK MoD is kept within their budget.

As the temporal NETD of TI imaging systems decreases attention increasingly turns to the uniformity of the presented imagery. This uniformity begins to limit the ultimate recognition and identification ranges of the system. This is true both of staring arrays and long linear detector based systems. This paper discusses the design, implementation and integration of a very high performance non-uniformity correction approach within the STAIRS C production SXGA resolution camera and presents preliminary findings.

The effect of radiation on HgCdTe photodiodes is an important parameter to understand when determining the long-term performance limitations for the Cross-track Infrared Sounder (CrIS), a Fourier Transform interferometric sensor that will fly as part of the National Polar-orbiting Operational Environmental Satellite System (NPOESS). The CrIS sensor uses relatively large area photovoltaic detectors, 1 mm in diameter. Each p-on-n HgCdTe photodiode consists of MBE grown, n-type material on lattice matched CdZnTe, with arsenic implantation used to form the junction. A 1mm diameter detector is achieved by using a lateral collection architecture. Solar, and trapped protons are a significant source of radiation in the NPOESS 833 km orbits. We irradiated 22 LWIR detectors with protons at the Harvard Cyclotron Laboratory (HCL) and monitored the I-V performance and dynamic impedance of each detector. Three groups of detectors were irradiated with either 44, 99, or 153-MeV protons, each between 1×10¹⁰ - 4×10¹² p⁺/cm². Several I-V data sets were collected within that fluence range at all three energies. All the detectors were warmed to room temperature for approximately 96 hours following the largest proton dose, re-cooled, and then re-characterized in terms of I-V performance and dynamic impedance. The total noise increase predicted for CrIS after 7-years in orbit is less than 1%.

This paper presents an overview of LETI infrared laboratory activity in the field of dual band infrared focal plane arrays. The technology developed uses HgCdTe multi-layer doped heterostructures grown by molecular beam epitaxy (MBE) on lattice matched CdZnTe high quality substrates. The device structure is n+ppn and is spatially coherent. The long wavelength layer is a planar like n⁺/p diode made by ion implantation while the shorter wavelength p-n diode is made in-situ during the MBE growth using Indium impurity doping. The last junction is isolated by mesa etch. The detectors are interconnected by indium bumps to a readout circuit with a yield close to 100 %. One or two indium bumps per pixel are used to address sequentially or simultaneously the two wavelengths, the detector pitch being 50μm or 60μm respectively. Elementary detectors exhibit performances in each band that are close to those obtained in single colour detectors with our standard technology. The Si-CMOS readout circuits are specially designed to optimise the performances of the infrared FPAs in both wavelengths. The electro-optical performances of two-colour FPAs with a complexity of 128×128 pixels operating sequentially within the middle wavelength infrared range (MWIR) at 77K are presented.

We report on the development and application of dual-band infrared focal plane array (FPA) technology to problems of interest to the U. S. military. For tactical applications, we show the application of dual-band MWIR/LWIR FPAs to reconnaissance, surveillance, and target acquisition. We show field test results of dual-band imaging of military targets over a diurnal cycle. We describe the development of a new dual-band LWIR/LWIR FPA for detection of the disturbed soil features associated with buried land mines. Finally, we will describe the application of dual-band FPAs in the strategic defense arena. We present dual-band MWIR/LWIR imagery of commercial launch vehicles that shows the utility of such an FPA for a sensor in a boost-phase interceptor.

Nova's development of the "Modular Infrared Imaging Applications Development System" (MIRIADS) produced a longwave infrared (LWIR) camera system that operated the "Adaptive Infrared Sensor" (AIRS) focal plane device produced by the Raytheon Infrared Operations (RIO) organization. A novel system architecture permitted the integration of an infrared fisheye lens system produced by Optics 1, Inc., which permitted a complete hemispherical field of view to be imaged onto the AIRS FPA. This paper will describe applications for this system as an extremely wide field-of-view IR sensor (early warning detection, fire detection, etc.), and will present test imagery collected with the system. This technology advancement has been the result of the coordinated effort of a variety of companies and government agencies. This presentation will highlight significant contributions of individuals and will indicate the effectiveness of the Small Business Innovative Research (SBIR) program in helping to advance this nation's technology base.

Rockwell Scientific's 3rd generation FPAs and sensor chip assemblies (SCA) are complete imaging systems-on-chip for IR and visible cameras. They provide 12-bit to 16-bit digital video at very low power consumption in hybrid and monolithic configurations. A 1936 by 1088 i-SoC with 5μm pixel pitch performs stand-alone visible imaging and a related application-specific integrated circuit supports SCAs. The former generates high-definition video at 30 Hz with <30 e-read noise, -80 dB fixed pattern noise and up to 70dB dynamic range at standard 2/3 inch optical format. When coupled to a fiber optic faceplate with micro-channel plate, the i-SoC for HDTV is believed the first for low-light-level HDTV imaging with 12-bit output at <200 mW. The latter, currently being developed to revolutionize space-and ground-based astronomy, is optimized for HAWAII-2RG 2048×2048 FPAs to provide 16-bit video at approximately 10mW for 10 Mbps imaging. The ASIC will help build very large mosaics for next-generation telescope sensors.

Visible (VIS) camera (such as CCD) or Near Infrared (NIR) camera (such as low light level CCD or image intensifier) has high resolution and is easy to distinguish enemy and foe, but it cannot see through thin fog/cloud, heavy smoke/dust, foliage, camouflage, and darkness. The Long Infrared (LIR) imager can overcome above problems, but the resolution is too low and it cannot see the NIR aiming light from enemy. The best solution is to fuse the VIS/NIR and LIR sensors to overcome their shortcomings and take advantages of both sensors. In order to see the same target without parallax, the fusio system must have a common optical aperature. In this paper, three common optical apertures are designed: common reflective objective lens, common beam splitter, and common transmissive objective lens. The first one has very small field of view and the second one needs two heads, so the best choice is the third one, but we must find suitable optical materials and correct the color aberrations from 0.6 to 12 μ. It is a tough job. By choosing ZnSe as the first common piece of the objective lens and using glass for NIR and Ge (or IR glass) for LIR as rest pieces, we only need to and are able to correct the aberrations from 0.6 to 1.0 μ for NIR and from 8 to 12 μ for LIR. Finally, a common reflective objective lens and the common beam splitter are also successfully designed. Five application examples are given. In the digital signal processing, we use only one Altera chip. After inserting data, scaling the image size, and adjusting the signal level, the LIR will have the same format and same pixel number of the VIS/NIR, so real-time pixel-by-pixel sensor fusion is realized. The digital output can be used for further image processing and automatic target recognition, such as if we overlap the LIR image on the VIS/NIR image for missile guidance or rifle sight we don't need to worry about the time and the environment again. A gum-size wireless transmitter is also designed that is able to send the VIS/NIR image, the LIR image, and the fused image to the rear commander 1 km away. The cost of the fusion system is less than $12 K, and a patent is granted to Zybron in April of 2002.

The recent fighting activities in various parts of the world highlighted the need for accurate targeting on one hand and real time reconnaissance capabilities on the other hand. Both needs can be met by means of targeting pod or reconnaissance pod, which enhance dramatically the aircraft task efficiency. Sharing common concept in design and architecture for the two types of pods reduces much of the overhead, required to operate two different pods in two different missions. Litening and Reccelite share a common design concept and are the perfect example for such savings.The design and built of a modern targeting / navigation / reconnaissance pod is governed by sets of requirements issued by the operators. This can be translated into the following design criteria: I. Design to be able to meet each customer specific requirements. II. Design to accommodate multiple sensors. III. Maintain capability for extensive signal and image processing capabilities, including future growth potential. In order to meet these design criteria, an optimized concept was resented and exercised for both Litening and Reccelite. All major sensing devices were placed in the front section 'on the gimbals' and all the signal processing boards were placed in the aft section in a special 'Video Unit'. While this concept enabled the designer to optimize the optical design for each sensor, it also introduced the need to optimize other system parameters. This article discusses the optimization processes, and also show how Litening and Reccelite designers successfully managed to introduce excellent solutions for the other system parameters : transferring high resolution video signals between the front and aft sections, electronic stabilization and 'open architecture' video processing unit to accommodate present and future capabilities.

In this paper we present a long Infrared Detector (LIRD) with Time Delayed Integration (TDI) mechanism in the 3mm - 5mm spectral band. The detector consists of four segments that are 'butted' on a single substrate in a staggered format. A novel butting technique ensures high accuracy and extremely uniform temperature distribution along the array. Each detector segment (DS) consists of an advanced CMOS readout integrated circuit (ROIC) attached to a back-illuminated diode array. The diode array is implemented with SCD's proprietary high performance InSb process. The ROIC is designed and optimized to be used with high F#, 'slow scan rate' systems. Very low power dissipation is emphasized. In order to achieve high flexibility, the signal processor is externally programmable, enabling TDI operation with or without over-sampling on any combination of elements. Some other features include: Bi-directional operation, defective pixel de-selection, variable line rates and integration times, externally controlled gain and background subtraction capability. The paper presents electrical and radiometric predictions. Measured results that were performed on the first prototype are also presented.

This paper describes the results of a long, intensive research and development effort related to the subject of nonuniformity correction (NUC). The study has been performed in order to increase the performances of cooled and uncooled FLIR's. The causes of NUC instability have been investigated in parallel with a general approach used for a very high dynamic range, and for very low noise FLIR performances. The results of this research have been implemented on a special design, enhanced vision system (EVS), camera for lending applications, and on ucooled camera FLIR's. This paper contains measured data on optics temperature influence on FLIR performance and theoretical models to explain the measured data.

The ELOP dual band LOROP camera was designed as a payload of a 300 gal reconnaissance pod capable of being carried by a single-engineerd fighter aircrat like F-16. The optical arrangement provides coincidence of the IR and EO optical axes, as well as equality of the fields-of-view. These features allow the same sacn coverage to be achieved, and the same gimbals control software to be used for the visible-light-only, IR-only and simultaneous dual band photography. Because of intensive, broadband vibration existing in teh pod environment, special attention was given to image stabilization system. Nevertheless, residual vibraiton still exists in a wide frequency range spreading from zero frequency to the detector integration rate and beyond it. Hence, evaluation of the camera performance could not rely on the well-known analytical solutions for MTF_MOTION. The image motion is deinfed in terms of the Power Spectral Density throughout the whole frequency range of interest. The expected MTF_MOTION is calculated numerically using a statistical approach. Aspects of the staggered-structure IR detecotr application in oblique photography are discussed. Particuarly, the ground footprint of the IR detector is much wider along-scan than one of the EO detector, requiring considerations to be implemented in order to prevent IR image deformation.

The impact of aerodynamic flow upon the performance of an airborne optical system is becoming a critical issue in the development and engineering of IR electro-optic systems. The analysis of this impact is now in the state of the art of IR electro-optic system research. Significant effort has been made on this issue during recent years. In this work we describe a novel technique for aero-optic calculations. The technique is based on commercially available software. In this work CodeV is the optical ray tracing code and Fluent is the Computational Fluid Dynamics (CFD) code. The synergetic combination between the output of the CFD code and optical software leads to the development of the method. The optically relevant data from the CFD results is transformed into index of refraction field and introduced as an input to the optical code. It is important to note that the data must not necessarily be presented in an analytical form; rather it is introduced in the most general form - as a discrete set of values located at a non-uniform grid of points. The modified quadratic Shepard method has been adopted for the data interpolation. This enables a simple interface with virtually any software output. Such compatibility ensures that the technique can be easily extended for the solution of a whole spectrum of optical problems that involve arbitrary index of refraction changes in the bulk and arbitrary optical surface shapes. For example image quality degradation caused by dome heating can be easily assessed. Both index of refraction changes of the dome and dome shape distortion being taken into account. Several numerical simulations demonstrating the technique are presented.

In this work we demonstrated multicolor quantum dot IR photodetectors with normal incidence background limited performance at 70K. The devices, which were studied in this work, were composed of self-assembled InAs dots grown by MBE on InAlAs barrier lattice matched to InP substrate. Normal incidence photocurrent spectra reveal several polarized and unpolarized peaks in the range 100-350 meV due to the intersubband transitions. The detector resonsivity at normal incidence is similar to that obtained for polarization normal to the layers, and is comparable to that achieved in quatnum well IR photodetectors.

Registration of images deals with finding geometrical warp parameters between different images with some common intrinsic details. The registration plays one of the most important roles in the super-resolution reconstruction since the latter deals with recovery of one high-resolution image from warped, blurred and decimated replicas of it. Several algorithms were already proposed for the general solution of the image registration. In this paper we concentrate on pure translations case. We use previous basic ideas and results to develop a new registration technique, which uses multiple reference frames, works with hardly aliased images and brings high subpixel precisions.

A decision of choosing the right detector technology for third generation thermal imaging systems is directly derived from the expectations and the requirements of these systems. It is now evident that third gen. thermal imager will still need the higher resolution capabilities as well as capabilities in multispectral detection and polarization sensitivity. Four technologies candidates are analyzed; the field-proved HgCdTe (MCT), uncooled microbolometer technology, Antimonide based materials and quantum well infrared photodetectors (QWIP). Taking into accounts the risks, maturity and technologies gap of each technology, we claim that for non-strategic applications (not low background conditions), QWIP technology is the most favorite. The ternary and super lattice Antimonide based material group seems to be theoretically the best alternative, but are not recommended due to it maturity and the high risk involved in this technology. We anticipate large penetration of the uncooled detectors to the low-end and medium-end market. The HgCdTe will still be in progress due to the inertion of the large funding and the strategic importance of this detectors technology.

We propose that the antimonide family of semiconductors should be considered in some cases as a serious alternative to Mercury Cadmium Telluride (MCT) for the active region of next generation IR detectors, based on epitaxial materials. Among the alloys, epitaxial InAs_1-ySb_y on GaSb with 0.07 < y < 0.11 and In_1-zAl_zSb on InSb with 0 < z < 0.03 together span important regions of the MWIR atmospheric window, yet exhibit strains of less than 0.15%. Both InSb and GaSb are binary substrates available in high quality. The sensitivity of bandgap to composition in In_1-zAl_zSb is similar to that in MCT. However, in InAs_1-ySb_y this sensitivity is more than halved. In growth from the gas phase, the constraints on temperature stability are about 3 - 5 times lower than in MCT. Together, these characteristics make it easier to achieve high uniformity, particularly in InAs_1-ySb_y. Finally, high quality superlattices based on InAs/Ga_1-xIn_xSb can be grown by lattice matching to GaSb. This epitaxial material is emerging as an attractive alternative to MCT with a high degree of spatial uniformity and with an ability to span cut-off wavelengths from 3-20m in a single material system.

In this work we reporrt on strained controlled InP/InGaAs and strained compensated InP/InGaAs/InGaP quantum well IR photodetectors (QWIPS) that cover the spectral bands 8-11 μm and 4-6μm respectively. Two different approaches were demonstrated in this work. i) We explore the effect of introducing non lattice-matched InGaAs well in InP/InGaAs QWIP structures. We show that this enables to extend the QWIP operating wavelength up to 11.5 μm taking advantage of strain as a bandgap engineering design parameter. State of art QWIPs with peak detectivity at 8.5 μm of 8×10⁹ cmHz^1/2/W at 80K with 2pi FOV was demonstrated. ii) A high detectivity mid-IR QWIPs were demonstrated. These devices are based on strain compensated INGaAs/InP/InGaP multiquantum well structures, where the InGaP conduction band offset extends the wavelength detection range ino the mid-IR. Photodetectors with background-limited performance with detectivity of D^*_λ (BLIP)=3.2*10¹⁰ cmHz^1/2/W up to 110 K, were implemented. We conclude that InP/InGaAs material system is suitable fo multicolro QWIPs applications, particularly for two color QWIPs operating in the 8-12 and 3-5 microns range simultaneously.

To detect dim point targets in IR backgrounds, it is often necessary to examine targets in more than one image. A dynamic programming algorithm is a useful technique for a Track Before Detect (TBD) architecture implementation, designed to track and detect dim maneuvering targets from an image sequence under low SNR conditions. We will present a TBD architecture which combines a subpixel velocity module for detecting targest moving at subpixel velocities from frame to frame and a DPA module which integrates the signal for maneuvering targets, varying from straight line flight. The DPA does a search over all the possible state sequences, marking possible tracks by scanning each pixel in each frame and determining where it was likely to originate from in the previous image, assuming it is the true target. Each transition receives a score based on its probability of being a target track. The scores are functions of the pixels intensity, transition velocity and direction and are given while considering their surroundings and a-prior restrictions such as the allowed maneuvering. Finally, we represent a CFAR module, which allows us to determine if a target is present, and if so, where the target is present, and if so, where the target is. Data to be tested will include both real data and data which has been preregistered to minimize vibrations. The effect of vibrations will be discussed.

This paper reviews stray light phenomena (SLP) existing in a military platform and compares a classical method with a proposed new concept. The methods used are described as well as the ensuing tests and results. Specifically this paper deals with sun glare and ways to treat it in an airborne FLIR systems having a stabilized line of sight. Besides the obvious direct glare that appears when the sun is in the field of view, there is also an indirect glare originating from stray light due to internal reflections and scattering that appears even when the sun is out of the FOV. The classical method to deal with SLP is to use SLP software in the optic design phase. At times even after careful and organized computer simulation design some unexplained SLPs still appear. The new two-stage method developed to deal with the SLP includes the following iterations: A. Mapping all the appearances of stray light within the space around the system. B. Dealing with each stray light appearance by opto-mechanical corrections and returning to stage A to ensure that no stray light exists. These two stages were iterated automatically in a computerized laboratory setup opposite a sun simulator lamp. The results achieved up to now will be described.

A heretofore unsolved challenge is the completely automatic and accurate estimation of road boundaries in aerial images when the roads may be partially or completely locally occluded and clutter may be prevalent. In this paper we introduce a roadfinder that is effective in meeting this challenge with a new approach which improves the speed of the algorithm described by Barzohar et al. In the new approach we use a new initialization for the low-level algorithm, described by Barzohar and Cooper, to obtain a completely automatic roadfinder. All the parameters that we need are estimated, such as minimum and maximum road widths, gray level variation and polarity between road and backgrounds, edge strength threshold at the road boundaries and road direction. The approach modifies the low-level algorithm, described by Barzohar and Cooper by adding the use of a line-pair detecting procedure which identifies regions of interest for the low-level treatment. The roadfinder begins with a line-pair detection which identifies windows that search for road seeds, continues with one or more seeds on each long road, and then accurately estimates the remaining boundaries. The algorithm is robust to missing boundary edges on one side of the road and on both sides of the road simultaneously. It is also robust to clutter within the road caused by cars or trucks, and to clutter resulting from two intersecting or adjacent roads. The quality performance of the automatic roadfinder in the five tested road images is based on statistical target recognition techniques, using a manual corresponding reference for each of the five different real images. This performance is very impressive, with probabilty of road detection equal to 1 and probability of false alarm equal to 0, i.e. all roads in the five images were detected. The estimation of the average accuracy of our roadfinder is equal to 0.68 pixel, which expresses the average distance between the extracted roads image and the reference roads in the five images.

SCD Focal Plane Arrays (FPAs) are based on 320×256 InSb elements, or 640×512 InSb elements. In this paper we introduce the outstanding FPA based on the signal processor 'blue fairy' (BF) that has been designed at SCD, and is now in standard production for the 320×256 InSb FPAs. The BF Focal Plane Processor (FPP) enables integration capacity of more than 15Me- at Integrate While Read (IWR) mode, and more than 30 Me- at Integrate Than Read (ITR) mode. A combined mode for large dynamic range with high sensitivity is possible. An excellent linearity and residual non-uniformity is achieved, starting from extremely low electron capacity up to 13Me- at IWR mode and 24Me- at ITR mode. Many other modes can be selected via a communication channel such as: ITR/IWR, one of seven different gains, one of seven different biases for the detector, windows size and window location. A Correlated Double Sampling (CDS) between frames and rows can be used for low frequency noise reduction, and/or any external electronic gain and offset drift corrections. All these features enable the integration of the BF FPA in large variety application, with high performance at each application.

A candidate for IR detectors for third generation thermal imageing systems is the QWIP. ELOP has gone through five years of development and evaluation of QWIP focal plane arrays and QWIP based thermal imaging system as a technology demonstrator. The R/D results are 320×256 QWIP based thermal imaging system operating in the 8-10μm band and a QWIP focal lpane array that operates simultaneously at the LWIR and NIR. A few aspects of commercializaiton of the QWIP are described focusing on the dark current issue. The QWIP as a multispectral sensor is referred to, especially the sensitivity of the QWIP by means of NETD in comparison with other optional multispectral detectors.

Rugate optical coatings are films, in which the refractive index is varied in a continuous or quasi-continuous manner. These films are used in order to obtain an optical response that is otherwise difficult to achieve. The application of rugate filters is done by a periodical variation of the refractive index, e.g. sinusoidally. The average index and the index modulation determine the filter bandwidth, and the cycle period determines the notch position. Another unconventional method for filter design, also based on a periodical index variation, is the bragg method, in which notch filters are designed by combining very thin layers of one material in a matrix of another, each unit being λ₀ /2 optical thickness. At the Rafael Optical Coating Center, a CO₂ suppression notch filter was developed using both these methods. A 24 cycles digital rugate film was used to achieve a narrow notch filter with bandwidth of Δλ/λ=6.8%, the transmittance in the blocked area was 13%, and 90% in the rest of the 3-5μm region. With 58 layers bragg film, the achieved blocking was even better - 6% transmittance in the blocking-band center, with a nearly similar transmission in the non- blocked zone.

Cameras for remote sensing and for long range reconnaissance on airborne and space platforms in the 0.4-1.0 μm region exist, but there is a growing need for images in longer IR wavelengths. In those wavelength regions, large apertures are essential to achieve satisfactory ground resolution but this conflicts with the limitations of weight often associated with long-range reconnaissance platforms. The high costs of the system itself and of its installation on the platform make it advantageous to provide both wavelength bands in a single instrument. A dual-waveband airborne telescope and camera system has been developed by El-Op Ltd. which will provide high-resolution images in the thermal IR at night and in the visible in daylight, or both simultaneously. It offers low weight, compact size and high dimensional stability over a wide range of environmental conditions. The two detector arrays are mounted in a compact focal plane assembly with a spectral beam-splitting system that optimizes the transmittance of each band. A cooled IR detector is essential to achieve the necessary sensitivity and a special detector array with a high reliability, lightweight, low power cooling unit has been developed.

Conventional optical elements have been replaced by diffractive ones in order to improve the performance of IR optical systems. Two examples are represented here.The first optical system is a MWIR scanning objective composed of air spaced doublet of CaF2 and As2S3 lenses. The combination of these materials gives an achromatic and passively athermalised optical system. It has been required to replace the As2S3 by an environmental approved material while retaining the achromatic and passively athermalised qualities. A new objective composed of ZnSe and Germanium lenses, where one of the Germanium surfaces is a diffractive one, has been designed to be also achromatic and passively athermalised. The two designs share similar optical performance. The second optical system is an objective for InSb Focal Plane Array Sensor at the MWIR spectral range. The optics includes ZnS, CaF₂, Silicon and Germanium lenses. The requirement is to image a 1.06 micron laser spot on the InSb sensor. A new design composed of a front ZnS lens and 5 ZnSe lenses enables the transmittance of both the MWIR and the 1.06 micron spectral bands. Two diffractive surfaces are added to correct the chromatic aberration at the MWIR. A third diffractive surface enables focusing the 1.06 micron spot at the same plane as the MWIR image.

A high performance FPP for a 640x512 infrared detector has been developed at SCD, comprising an internal analog to digital conversion. The conversion resolution is 13/15 bits, selectable via a serial communication channel. The focal plane power dissipation at an output rate of 100 Frames per Second is less than 130mW, yielding about 0.1 pJ/conversion bit. A 0.5 micron double poly triple metal process was used, yielding a pixel capacity of greater or equal to 13 Me-. The serial communication link enables also user control of the operating modes, full-scale range gain and windowing. The processor is designed as a multi-chip system with an external FPGA, enabling an un-usual flexibility and easy adaptation to the external system.

We report on a new, simple process to fabricate planar Hg_1-xCd_yTe/Hg_1-xCd_xTe heterostructure photodiodes with p-on-n configuration. The material used for this demonstration was a double-layer p-on-n heterostructure that was grown by a liquid-phase-epitaxy technique. The p-on-n planar devices consisted of an arsenic-doped p-type cap epilayer on top of a long-wavelength IR n-type active epilayer. The ion-beam-miling p-type conversion effect was used to delineate the active device element, and to isolate the planar device. Detailed analysis of the current characteristics of these diodes as a funciton of temperatuer, show that they have high performance, and that their dark current is diffusion-limited down to 60 K. The results show that over a wide range of cut-off wavelengths, the RoA product values are close to the theoretical limit. Light Beam Induced Current technique was used to characterize the lateral and vertical dimensions of the ion beam milling induced junction. Electro-optic properties of a 2D array of small diodes with a 40-μm pitch are presented, and demonstrate the potential of the new process for implementation of 2D arrays.

Modern electro-optic applications often contain a cryogenically cooled IR imager placed upon a stabilized platform which is connected to an outer housing by low-friction gimbals. Since the active system of gumball stabilization is dedicated primarily to maintaining the steady line-of-sight control by eliminating the relatively slow effects of yaw, pitch or roll, it may have insufficient resources to suppress an excessive high-frequency vibration exported from the internal active components such as the linear compressor of a cryogenic cooler. To reduce the above vibration export, the authores use an optimally stiffened and damped all-metal vibration isolator is combination with a tuned dynamic absorber. For effective heat sinking, a commercially available metallic plain bearing allowing the compressor to slide freely inside the above plain bearing, which is further thermally connected to the appropriate 'cold wall' of the device. The vibration protective and thermally conductive interface developed allows the use of a split Stirling cryocooler, relying on a highly efficient, cheap and durable linear single-piston compressor within the IR imager mounted upon the gimbaled stabilized platform.

The use of large diameter diffractive and aspheric Silicon elements for 3-5μ IR lens assemblies have many advantages for the user, such as low weight and ow raw material costs. However, difficulties in diamond turning large diameter Silicon lenses, resulting in low quality optical surfaces and high manufacturing costs, practically prevented the use of these elements. Recent advances in diamond turning manufacturing and measurements technologies enable now the design and manufacture of large diameter diffractive and aspheric Silicon elements with high optical quality and reasonable costs. We will present some lens designs and measured performance of these Silicon elements.

During the last decade we have investigated the synthesis, growth and characterization of CdTe and CdZnTe semiconductor compounds. As a result, substrate crystals, suitable for mercury cadmium telluride thin film growth are prepared. The emphasis will be given to the investigation of the thermal regime during growth, reflected at the solid liquid interface shape and its influence on the crystalline quality. Seeded and unseeded growth experiments are compared in terms of structural crystalline quality. Seeded and unseeded growth experiments are compared in terms of structural crystalline perfection as well as single crystal yield. The effect of thermal annealing on IR transmittance, precipitates and inclusions will be discussed in detail. Moreover, we will show the recent new trends for simulation of crystal growth processes by CRYSVUN software as well as practical implementation of calculated data for the grwoth of II-VI crystals. Preliminary study on the vapor phase control during growth and crystal cooling procedures will also be discussed.

An infrared focal plane array (FPA) non-uniformity correction (NUC) method is considered, in which two-point calibration (TPC) table is calculated and stored at the factory, and the offset correction is carried out periodically during the mission. An InSb FPA is examined, and the stability of the NUC is measured over various periods (up to 9 months) and also under variations of the FPA temperature and integration time. We find that the NUC quality and its stability comply with the system requirements. We find, also, that the stability of the NUC is better maintained by using a single TPC table for the entire detector dynamic range, as compared to the multiple (piece-wise-linear) TPC. A simple phenomenological model of the detector non-linearity is proposed, which fits the experimental data better than the quadratic non-linearity model.

The design optimization of a dewar with a very large cold stage, for flight applications, is described. The optimization was achieved with the aid of Cosmos/m Finite Elements software, in order to arrive at a dewar of minimum weight. The design concept incorporate a symmetrical base, which includes cavities and ribs. The number and dimensions of the frame ribs were varied in order to arrive at weight optimization consistent with maintaining the cold stage natural frequency and deflections within the required limits. The final result of this weight optimization process was a dewar with a 25% weight reduction as compared with a more conventional dewar wiht a solid base. The weight of the new dewar, the natural frequencies and center of mass location were 522gm, 1095Hz, 1435Hz, 2022Hz, 3239Hz 0, 17.4mm, 0, respectively. The weight of the traditional dewar, the natural frequencies and center of mass location were 709gm, 1080Hz, 1411Hz, 2111Hz, 3230Hz, 0,15.0mm, 0, repsectively.

High-resolution IR scanning systems able to scan large areas quickly require linear detector arrays with more than 1000 elements and high sensitivity, achieved by TDI. ELOP initiated the development of such a long detector array in the 3-5μm spectral region. The architecture of the detector is based on several sub-segments butted together in a staggered configuration to achieve the desired detector length. One problem is the large non-uniformity of the detector, which is exacerbated by the cos⁴α optical effect. With the entrance pupil imaged on the cold shield aperture to enhance efficiency, the angle a becomes large. This imposes significant additional non-uniformity that has to be compensated and affects the dynamic range of the electronics. A way to overcome this problem is suggested, based on de-selecting specific pixels in any TDI channel. Another problem is that while higher TDI levels increase the SNR, they increase the smear (blur) due to vibrations, drift etc. The optimal TDI level depends on the specific conditions of the system, namely: signal level and vibrations. Using superfluous pixels in the overlap between segments, several TDI levels can be operated simultaneously, allowing a decision to be made automatically as to the optimal TDI level for operation.

An accurate model for propagation of infrared energy within the marine atmospheric surface layer remains an elusive goal. Within the first tens of meters of elevation above the sea surface there are substantial vertical gradients of mass and temperature. This has a strong effect on the prediction of extinction of the infrared signal. There exist models to enable the computation of the effects generated by these factors, but often these models contribute only extinction factors. The refractive propagation factor is proposed as a critical component of an accurate transmission model within the marine surface layer. The propagation factor is a multiplicative quantity that is derived entirely from the local refractive field and the geometry of the entire transmission system. A ray-trace model is used to compute the refractive magnification or minification. The ray-trace model also elucidates the importance of mirage images to account for all energy received at the sensor. I will present a comparison of the model with field data that contain episodes of anomalously large signal intensities. The core thesis of this paper is that the necessary final component in a complete model for near-sea-surface infrared transmission is the propagation factor induced by refractive effects.

NATO Task group TG16 is cooperating on topics related to ship self-defence. One of these topics is related to IR Search and Track sensors, which are in development for detection of low altitude air targets. In particular the group is working on models to predict the range performance of these sensors. Newly developed models include marine boundary layer effects such as refraction due to temperature gradients, scintillation due to turbulence and particle size distributions. TG16 organized in May 2001a trial in the Mediterranean Sea near Livorno, Italy, called POLLEX to further validate these models. Seven nations particulated with complementary instruments for measurements of the target signatures and environmental characteristics. Three targets were provided, a series of small visual/IR sources at a fixed distance, visual/IR soruces on a ship moving in and out up-to and beyond the horizon and a helicopter. The weather conditions during the measurement period showed interesting variations in Air to Sea Temperature DIfference and atmospheric turbulence. Data have been analzyed and samples of the results, as collected and/or analyzed by the participants, are discussed in this paper.

Ballistic Missile Defense has been set as a national priority for the Department of Defense. IR focal plane arrays (IRFPAs) are needed for ballistic missile defense (BMD), as well as many other military systems. BMD IRFPA applications extend from surveillance using ground, airborne and space-based platforms, to both endo- and exo-atmospheric interceptor seekers. Even though IRFPAs using material systems, such as HgCdTe and InSb, are adequate for most tactical military applications, certain IR systems for BMD exert a much more stringent requirements. For example, when IRFPAs are used in a system where the target is very cold, the background noise is orders of magnitudes lower than tactical scenes. In this case, the total noise of the IRFPA is dominated by the internal detector noise. With a cold dim target at a far away distance, IRFPAs with extended wavelengths are needed to receive as many photons as possible. The requirements of BMD IRFPAs with high sensitivity, large format, small pixel size and high frame rate, plus long cutoff wavelength and operating at low temperatures presents great challenges to IRFPA technology. Multi-color FPAs and active/passive fusion can greatly enhance the important task of discrimination and aim point selection.

Many target-tracking applications require an optical system to acquire the target in a wide field of view and then switch to a narrow field of view for tracking, and identification. This process is complicated by the time required, and the resulting loss of image data during the FOV switch. The objective of the investigation was to develop a dual field of view infrared lens system that could accomplish the FOV switch without the loss of any image data. The design was based on achieving this requirement with the lens system integrated with a range of commercially available mid wave infrared cameras. The results of trade studies and evaluation of user mission profiles, resulted in a system with 100mm and 500mm focal lengths, with a field of view switch within one frame period. The FOV switch was further required to coordinate with the frame synchronization timing to eliminate any loss of data during the FOV change. The requirements also specified a fully integrated system housed in a sealed enclosure that would support extended field deployment in a military environment with no maintenance. Presented herein are details of the design trade studies and specification development, highlights of the resulting optical design with a discussion of the optimization methods employed. Also included are details of the packaging challenges and solutions and sample performance data collected from successful field tests of the first two prototype units.

Many applications of infrared technology require the use of narrow bandpass filters with excellent out-of-band rejection. Frequently, system designs require that the filter be placed in close proximity to a detector or focal plane array. More than twenty-five years ago Donald Stierwalt discovered that some filters that met out-of-band rejection specifications in a spectrophotometer did not meet specification when integrated into a focal plane assembly. In fact, he reported that proximal to the detector, one filter passed three orders of magnitude more out-of-band light. Since then, the Stierwalt Effect has become widely quoted and poorly studied. Many assume that it has to do with scatter in the film, but very little data has been reported. Here, we report the observation of the Stierwalt effect in an optical filter that was seeded with model defects. The seeding was done by depositing sparse 1μm polystyrene spheres upon a clean substrate before sputter depositing a simple band-stop filter. Light rejection from filters prepared in this way showed a strong dependence upon the distance between the film and the detector. Filters deposited without the spheres showed a much smaller effect.

Next generation IR Search and Track Sensors (IRSTs) will use IR Focal Plane Arrays (IRFPAs) because of their benefit concerning increased sensitivity, higher update rate and inhernet capability of enhanced processing. Moreover the full stare RIST concept allows a more flexible set-up on the platform to be protected such as ships, airplanes or air defence sites. The increased sensitivity is primarily a consequence of the large amount of detector elements in use, leading to longer integration times in comparison with present generation IRSTs. If increased sensitivity is not required, a trade-off can be made on dimensions of the optics, the most vulnurable part of the system. It was found during a series of experiments at various locations, that in many occasions optical phenomena in the marine boundary layer, such as sub-refraction and scintillation, provide additional sensitivity, when appropriate signal handling is used. Of course this enhanced sensitivity is partly reduced by the greater extinction in this boundary layer due to higher relative humidity and aerosol concentration. These phenomena have been investigated in great detail and new models tend to predict their magnitude when adequate input parameters are used. This paper describes the basics of next generation IRSTs and the results of the investigations on enhanced IR point target detection performance by proper use of the atmospheric 'multiplier' effects.

The Passive InfraRed Airborne Tracking Equipment (PIRATE) has been developed for the Eurofighter aircraft. The equipment is mounted in the forward fuselage and fully integrated into the weapon system. PIRATE is fundamentally a Track While Scan infrared search and track (IRST) system which also performs conventional navigation FLIR functions. In the primary air-air role, the equipment passively detects, tracks, classifies and prioritizes multiple airborne targets under all aspects, look-up, look-down and co-altitude conditions. The IRST functions are fully integrated into the aircraft attack and identification sub-system and can be diverted to specific search and track areas as a result of commands on the communication bus. The pilot has several selectable operating modes depending upon the particular combat mission requirement. The priority functions are to search specific scan volumes in conjunction with other aircraft sensors in a Multiple Target Track Mode. Imaging modes are used to visually identify single targets of particular interest or to generate IR images of the scene as a general flying aid or landing aid in bad weather or night time conditions. These images are displayed on the Head Up Display (HUD), Multifunction Head Down Display (MHDD) or the pilots helmet visor. The primary functions, system design overview and the application of current technologies will be presented.

In the science of Infrared Thermography, all objects emit electromagnetic radiation of a wavelength dependent on the object's temperature. This radiation is detected and measured with infrared radiometers (IR imagers). The imagers contain an infrared detector that converts the emitting radiation into electrical signals that are displayed on a gray-scale or color display monitor. Each IR radiometer is designed to receive the naturally emitted radiation energy in a specific spectrum band such as 3-5 um (short wave) or 8-12 um (long wave). EnTech Engineering, Inc. has developed a system, based upon both ground and aerial mounted Infrared Thermographic technologies, capable of detecting buried pipelines, detecting leaks in these hidden pipelines, and mapping both the pipelines and their leaks. EnTech® Engineering, Inc's patented INSITE II, Infrared Thermography based Buried Pipeline Mapping & Leak Detection System uses a custom designed high resolution, wide band, 3-12 um, Infrared detector. This infrared scanning system produces a temperature map (thermogram) consisting of thousands of individual thermal readings repeated 60 times per second. The thermal images, or thermograms, are recorded and stored on digital instrumentation videotape. This thermogram is then modified to work within EnTech® Engineering, Inc.'s patented data collection and analysis hardware and software. After the thermal data is processed, it can be displayed on a monitor in multiple shades of gray-scale or color. The colors displayed on the thermogram are arbitrarily set by the Thermographer to best illustrate the infrared data being analyzed. The scope of service for this project was to perform an EnTech® INSITE II, Infrared Thermographic Subsurface Pipeline & Pipeline Leak investigation on an approximately 7,500 feet long by 300 feet wide, 2,250,000 square feet, 52 acre, potential railroad yard site located in Texas. The purpose of the investigation was the detection of surface thermal anomalies indicative of, but not limited to

An electrostatic MEMS actuator, known as the "Artificial Eyelid," can be used as a micromechanical chopper for uncooled IR detectors such as pyroelectrics and microbolometers. These flexible film actuators act as tightly curled shutters, providing transmission of IR radiation to the sensor elements when open and reflection of the IR when closed. The actuator structure consists of a curled polymer/metal film stack which is microfabricated and released from an IR transparent substrate. The film stack is uncurled by applying an electric field between the curled film and the transparent fixed electrode on the substrate. Devices produced to date have ranged in size from 50 microns to 2 mm on a side and can be fabricated in array form to chop the IR signal for a FPA. Recently, 4 x 4 mm arrays with actuator elements ranging in size from 250 x 600 microns to 600 x 1000 microns have been fabricated with 95-100% of the elements functioning at 150-280 V. Current status of the development of these actuators and testing of micromechanical chopper arrays will be discussed.

Astronomical arrays operating at (sub)millimeter wavelengths are seriously compromised by rapid variations in atmospheric water vapor that distort the phase coherence of incoming celestial signals. The signal received by each antenna of the array suffers a phase delay that varies rapidly with time and from antenna to antenna. Unless corrected, these distortions limit the coherence time of the array and seriously compromise its sensitivity and image quality. Building on the success of a prototype infrared radiometer for millimeter astronomy (IRMA), which operates in the 20μm region to measure the column abundance of atmospheric water vapor, this paper describes the latest version of the IRMA concept, which has been developed for operation at Llano de Chajnantor, future site of the Atacama Large Millimeter Array (ALMA). Since there is presently limited infrastructure at the Chilean site the design must pay careful attention to all aspects of remote operation.

This paper reports on the development of a new class of thermal cameras. Known as the FLAsh STabilized (FLAST) thermal imaging camera systme, these cameras are the first to be able to capture snapshop thermal images. Results from testing of the prototype unit will be presented and status on the design of amore efficient, miniaturized version for produciotn. The camera is highly programmable for images capture method, shot sequence, and shot quantity. To achieve the ability to operate in a snapship mode, the FLAST camera is designed to function without the need for cooling or other thermal regulation. In addition, the camera can operate over extended periods without the need for re-calibration. Thus, the cemera does not require a shutter, chopper or user inserted imager blocking system. This camera is capable operating for weeks using standard AA batteries. The initial camera configuration provides an image resolution of 320 x 240 and is able to turn-on and capture an image within approximately 1/4 sec. The FLAST camera operates autonomously, to collect, catalog and store over 500 images. Any interface and relay system capable of video formatted input will be able to serve as the image download transmission system.

The emergence of uncooled infrared detectors has opened new opportunities for IR imaging both for military and civil applications. Infrared imaging sensors that operate without cryogenic cooling have the potential to provide the military or civilian users with infrared vision capabilities packaged in a camera of extremely small size, weight and power. Uncooled infrared sensor technology has advanced rapidly in the past few years. Higher performance sensors, electronics integration at the sensor, and new concepts for signal processing are generating advanced infrared focal plane arrays. This would significantly reduce the cost and accelerate the implementation of sensors for applications such as surveillance or predictive maintenance. We present the uncooled infrared detector operation principle and the development at CEA/LETI from the 256×64 with a pitch of 50 μm to the 320×240 with a pitch of 35 μm. LETI has been involved in Amorphous Silicon uncooled microbolometer development since 1992. This silicon IR detection is now well mastered and matured so that industrial transfer of LETI technology was performed in 2000 towards Sofradir. Industrial production of 320 μ240 microbolometer array with 45μm pitch is then started., we present the readout circuit architectures designs and its evolution from the 256×64 array to the different version of 320×240 arrays. Electro-optical results obtained from these IRCMOS are presented. NEDT close to 30 mK is now obtained with our standard microbolometer amorphous silicon technology.

A new concept for embedded fiber optic temperature sensor is described. In this sensor the temperature is inferred by analyzing the infrared radiation, which is emitted from the tip of an infrared transmitting optical fiber. The sensor can be adjusted for ambient or high temperature measurements and has a spatial resolution approximately equal to the diameter of the optical fiber. The measurement is immune to changes that can occur along the embedded fiber. Inferring the temperature directly from thermal radiation makes this technique both more accurate and simple relative to other embedded fiber optic temperature sensors. A prototype sensor was constructed by embedding silver halide optical fibers in epoxy and the sensor was used to monitor the temperature of the epoxy. Preliminary results are described which prove the validity of the new technique. Such a sensor can be useful for temperature measurements of smart structures.

We present a novel dry micromachining technique for the release of the thermally isolated spiral thermocouples, which achieve the highest thermal resistance for a rectangular pixel with a fixed size. The sensors are fabricated using mask-less post-processing of standard CMOS chips that contain CMOS readout electronics. Basic 1D thermal modeling of the sensors is presented and its limitations. Analysis of the performance of the sensors is derived from the modeling. Mechanical resonant frequencies for the structures are also shown. Design of such sensors in standard CMOS technology is reviewed, as well as results of fabricated devices. Fabricated devices include single elements and arrays up to 32*32 elements with pixel size and pitch of several tens of microns.

Until today, almost all objective lenses and windows of LIR imagers use crystal Germanium (Ge) as the optical material. Germanium is heavy, expensive and very sensitive to the environmental temperature change. When the temperature rises above 120° C, the lens becomes opaque. It is necessary to overcome these shortcomings. Using the analytic universal skew ray tracing formula and the automatic optical system design software developed by us, we successfully designed a 150mm/F1 objective lens using Ge and non-Ge materials for the LIR imager of the missile seeker and airborne surveillance. We also successfully designed a 25mm/F1 objective lens with large FOV of 30°x40° using only non-Ge materials for the LIR imager of the helmet mounted search and rescue system. Good image quality is obtained. The cost is less than half of the Ge lens and the high temperature resistance is much better. In order to increase the S/N ratio 4 times for the low-sensitivity UFPA, an immersed Ge lens for the UFPA is also successfully designed. Currently, most of UFPAs use high-cost Digital Signal Processing (DSP) module. The LIR imager needs at least two circuit boards. We present a design that uses low-cost Altera processor and the imager only needs one board without Thermal Electrical Cooler (TEC). Therefore, three "AA" batteries can operate the imager for more than 4 hours. By inserting data between pixels and enhance the contrast, the image from the 120x120/50μ UFPA is even better than the image from the 240x320/50μ array. This gives us an opportunity to reduce the imager cost to 2/3 of the larger format without degrading the image quality. These innovative researches give us a chance to build a small, lightweight, inexpensive, and good image quality LIR imager for homeland security and many other military and commercial applications. Two patents were pending and one was granted.