A feasibility study for the solar occultation observation from space has been carried out. An ordinary Michelson type Fourier transform spectrometer with 1 cm^-1 resolution and 10 Hz rapid sampling showed best feasibility by the trade offs among the sensitivity and resource consideration. For the low- cost and quick development, it is assumed to use design similar to a commercial laboratory model. By using 200 K TE cooled PC-MCT detector, it showed least resource requirement and the SNR greater than 150 over 800 to 3300 cm^-1. By using 80 K MCT, it is possible to achieve the SNR greater than 500 can be achieved with more resources for weight and power.

The SPIRIT III (spatial infrared imaging telescope) radiometer is the primary instrument aboard the midcourse space experiment (MSX), which was launched on 24 April 1997. The Space Dynamics Laboratory at Utah State University (SDL/USU) developed and implemented a ground-based procedure to optimize the focus of the SPIRIT III radiometer. The procedure used point source data acquired during ground measurements. These measurements were obtained with a calibration source consisting of an illuminated pinhole near the focus of a cryogenically cooled collimator. Simulated point source measurements were obtained at multiple focus positions by translating the pinhole along the optical axis inside and outside the optimum focus of the collimator. The radiometer was found to be slightly out of focus, and the detector focal plane arrays were moved to positions indicated by the test results. This method employed a single cryogenic cycle to measure both the distance and direction needed to adjust each array for optimal focus. The results of the SPIRIT III on- orbit stellar point source observation demonstrate the success of the technique. This paper describes the method and hardware used to achieve focus optimization.

A small bispectral infrared detection (BIRD) push broom scanner for a small satellite emission is described, which is dedicated to the detection and analysis of high temperature events (HTE). Current operating and planned satellite sensors are not designed for high temperature event observation and therefore show some serious drawbacks such as saturation of the IR channels for target temperatures higher than 50 degrees Celsius, low spatial resolution in case of daily coverage, low coverage of spatially high resolving systems, or not adequate IR channels. The BIRD instrumentation is a first attempt to overcome these disadvantages. For this purpose two infrared line scanners (3.4 - 4.2 micrometer and 8.5 - 9.3 micrometer) are combined with a wide angle stereo scanner (WAOSS) in the visible. Because of the limited resources of a small satellite the design of all instruments is based on the usage of staring focal plane arrays. To observe HTE directly the covered sounding area should be as large as possible whereas at first glance the ground resolution of the sensor should be in order of some 10 m. These demands are in contradiction with the number of the infrared detector array elements currently available. For this reason methods of subpixel target detection and analysis have to be used. According to this concept a combination of the data from at least to radiometric high sensitive infrared sensor channels is used to compensate the lack of high ground resolution. Adding to the infrared cameras a suitable CCD-line scanner for a pre-classification with a higher ground resolution, a marked improvement can be achieved.

We have designed a compact all-reflective near infrared (1 - 2.5 micrometer) long slit spectrograph and imager (CAIRS) for the UK infrared telescope (UKIRT). CAIRS will provide a comprehensive spectroscopic and imaging capability in the near infrared. In spectrograph mode, it uses one slit or two slits for use with image slicers so that it can be used to provide two-dimensional spectroscopy over an extended field. Different gratings can be used in order to reach resolving powers up to 5000. As the instrument uses only mirrors, there is no chromatic aberration and all primary aberrations are almost completely eliminated over a large field of view.

The wide-field infrared explorer (WIRE) is a cryogenically cooled infrared telescope designed to study the evolution of galaxies. Presented in this paper is the stray light design and analysis of WIRE. Unwanted radiation from off-axis sources such as the moon, and thermal emissions from the aperture shade are suppressed by the use of key stray light design features. These include the placement of the aperture stop at the secondary mirror, tapering of the main baffle vanes, and use of ring baffles for the secondary obscuration and outer ring. Details concerning the issues of baffle design, mirror scatter, and non-optical component scatter are provided. The point source transmission (PST) curve, which characterizes the sensor's off-axis response, and the aperture shade thermal contribution were computed using the stray light analysis program APART. The results indicate that the stray light impact on the WIRE mission is minimal.

An off-axis scatter facility was developed to support the Space Dynamics Laboratory in a number of earth limb measurement programs where the off-axis performance of the sensors was critical to the validity of the data. The facility was developed from three fundamental assumptions. (1) Careful control of any light scattered from the optical system being measured to make certain that it did not return to re-enter the system and corrupt the measurement. (2) Use of black specular surfaces in a unique shape to direct and attenuate scattered light. (3) Utilization of clean room technology to filter air to reduce scattering from particulates in the air and to prevent dust from degrading the specularity of the special surfaces. Therewithal analyses of atmospheric and surface scattering showed that surface scattering effects could be suppressed below atmospheric scattering limits by use of properly shaped specular walls. Analysis of measurements made in the facility demonstrated that the measurements were limited by Rayleigh scattering from the air molecules in the facility and not from dust or water droplets in the air nor from scattering from any chamber surfaces. Measurements of the Cassini narrow field camera showed a noise floor at 2.8E-12 of on-axis response.

The spatial infrared and imaging telescope (SPIRIT III) was flown aboard the Mid-Course Space Experiment (MSX), a Ballistic Missile Defense Organization sponsored program. SPIRIT III is a long-wave infrared instrument package consisting of a high off-axis rejection telescope, a five- color radiometer, and a six-channel interferometer. End-of- life temperature requirements for the radiometer, interferometer, telescope, and baffle are less than 12 K, less than 11.5 K, less than 20 K, and less than 70 K, respectively. Cooling for the instrument is provided by a single-stage, 9 K solid-hydrogen-filled cryostat. In November 1994, just prior to launch, the cryostat suffered a loss of vacuum in the insulation space, which resulted in extensive damage to it and the instrument. After months of investigation and analysis, it was determined that the primary cause of the vacuum loss was a stress corrosion failure in the cryogenic plumbing. A decision was made to rebuild portions of the cryostat and instrument, but because of time constraints and the way parts of the cryostat parts were bonded, many sections of multilayered (MLI) insulation were not replaced during the rebuild. To measure what impact, if any, the degraded insulation might have on thermal performance, a test using liquid helium was carried out prior to the MSX satellites' launch in April 1996. Once on orbit, temperatures inside the cryostat equilibriated, but the instrument temperatures ran warmer than expected despite the cryogen being near the predicted 9 Kelvin. The cryostat eventually ran out of cryogen one month short of the initial, on-orbit predictions. This paper describes the cryogenic system, illustrates the pre- launch thermal performance predictions, and discuses the on- orbit thermal performance.

Through analysis of spectral imaging data acquired with the airborne visible infrared imaging spectrometer (AVIRIS) from an ER-2 aircraft at 20 km altitude, it was found that narrow channels near the center of the strong 1.38 micrometer water vapor band are very sensitive in detecting thin cirrus clouds over different geographical regions. Based on this observation from AVIRIS data a channel centered at 1.375 micrometer with a width of 30 nm was selected for the moderate resolution imaging spectrometer (MODIS) for remote sensing of cirrus clouds from space. The sensitivity of this channel to detect thin cirrus clouds during the day time is expected to be one or two orders of magnitude better than the current infrared emission techniques. As a result, much larger fraction of the satellite data is expected to be identified as being covered by cirrus clouds. In order to make better studies of surface reflectance properties, thin cirrus effects must be removed from satellite images. We have developed an empirical algorithm for removing/correcting thin cirrus effects in the 0.4 - 1.0 micrometer region using channels near 1.375 micrometer. This algorithm will be incorporated into the present MODIS atmospheric correction algorithms for ocean color and land applications.

This new paper presents a nonlinear filtering technique for speckle noise reduction when the statistical clutter model is known. It is assumed that the noise or image statistical contributions are not known. The method has been successfully used for speckle noise reduction on electro-optical and SAR images for pre-filtering in multi-sensor image registration applications. A detailed software description of this speckle and noise reduction algorithm is also presented.

Due to the complex shape of particles, it is difficult to calculate the scattering matrix of the nonspherical cirrus particles exactly. One of the most widely used techniques to calculate the optical property of nonspherical cirrus particles is the geometrical optics approximation method. We describe the FORTRAN code to calculate a 4 by 4 scattering matrix of both convex and concave cirrus particles using the geometrical optics approximation method together with the Fraunhofer diffraction theory. The randomness of the ice crystal face is also considered. Examples of the scattering matrix are presented. In addition, we discuss the complexity of calculating nonspherical particles from the theoretical point of view.

An algorithm to derive the effect of the land surface on the emergent radiation from the top of the atmosphere in the coastal zone is proposed. The surface is simulated by checkerboard type of terrain composing pixels, either land or ocean. The look-up-table method is used for the atmosphere- surface correction, where two parameters based on the diffuse transmission and reflection function of the atmosphere are introduced to investigate the contribution of adjacent pixels. These parameters are independent of the surface reflection properties. At present, the ocean surface is in accordance with the Cox and Munk model surface, whereas that of land is assumed to be Lambertian. The upwelling radiation emerging from the top of the atmosphere is expressed by a sum of radiative interactions between the surface and the atmosphere, and it is simulated using these parameters and combinations until convergence. An example of numerical simulation is shown at a wavelength of 0.56 micrometer, which corresponds to the center wavelength of the shortest channel of ASTER on EOS-AM1. The dust-like model is used for the aerosols and the land surface albedo is 0.2 or 0.4. The ocean wind is 5 m/sec and the refractive index is 1.333. The effect of the land surface on the radiance over the ocean is stronger just off the coastal zone and decreases exponentially with increasing of distance from the land. It depends upon the solar zenith angle and atmospheric condition as well. The present new version enables us to quantitatively discuss radiative transfer over the non-uniform composite surface including coastal zone. A typical numerical simulation is performed over the Tsukuba lake area in Japan.

Cirrus cloud sounder (CCS) is a photopolarimeter with six radiation channels and a polarization channel. By CCS, cirrus cloud and other kinds of cloud can be detected from space by means of reflectance, cloud peak pressure, polarization and optical depth. For clear sky, atmospheric aerosols can be also sounded remotely from space. Linear, elliptical and circular polarization can be measured by the polarization channel.

We present the optical, mechanical and electronic design of MANIAC, the mid- and near-infrared array camera, together with some recent astronomical results. MANIAC is a two-channel intrument that offers observations from 1 to 5 micrometer and from 8 to 28 micrometer at the same time. The advantages of the purely reflective optical design of MANIAC are discussed as well as the options that are provided by simultaneous observations in the two regimes. The construction of MANIAC will be completed in a modular way, each of the five phases offering a fully operational instrument. Here, we report on completion of the first phase, a mid-infrared camera based on a Rockwell 128 by 128 pixel Si:As detector. With a pixel scale of about 0.2', the MANIAC mid-infrared channel offers diffraction-limited imaging in the N and Q bands at a 4m-class telescope and a field of view of 26' by 26'. The achieved sensitivity is very close to the background limit under all observational modes. We also discuss the scientific importance of high-resolution mid-infrared observations, describe the observing methods and characterize the performance of the detector array.

The analysis methodology and corresponding analytical tools for the design of optimized, low-noise, hard target return CO₂ differential absorption lidar (DIAL) receiver systems implementing both single element detectors and multi-pixel imaging arrays for passive/active, remote-sensing applications are presented. System parameters and components composing the receiver include: aperture, focal length, field of view, cold shield requirements, image plane dimensions, pixel dimensions, pixel pitch and fill factor, detection quantum efficiency, optical filter requirements, amplifier and temporal sampling parameters. The performance analysis is accomplished by calculating the system's CO₂ laser range response, total noise, optical geometric form factor and optical resolution. The noise components include speckle, photon noise due to signal, scene and atmospheric background, cold shield, and electronic noise. System resolution is simulated through cascaded optical transfer functions and incudes effects due to atmosphere, optics, image sampling, and system motion. Experimental results of a developmental single-element detector receiver designed to detect 100 ns wide laser pulses (10 - 100 kHz pulse repetition rates) backscattered from hard- targets at nominal ranges of 10 km are presented. The receiver sensitivity is near-background noise limited, given an 8.5 - 11.5 micrometer radiant optical bandwidth, with the total noise floor spectrally white for maximum pulse averaging efficiency.

The development and test results of a prototype detector/amplifier design for a background limited, pulsed 100 ns, 10 - 100 kHz repetition rate LIDAR/DIAL receiver system are presented. Design objectives include near-matched filter detection of received pulse amplitude and round trip time-of- flight, and the elimination of excess correlated detector/amplifier noise for optimal pulse averaging. A novel pole-zero cancellation amplifier, coupled with a state-of-the- art SBRC (Santa Barbara Research Center) infrared detector was implemented to meet design objectives. The pole-zero cancellation amplifier utilizes a tunable, pseudo-matched filter technique to match the width of the laser pulse to the shaping time of the filter for optimal SNR performance. Low frequency correlated noise, (1/f and drift noise) is rejected through a second order high gain feedback loop. The amplifier also employs an active detector bias stage minimizing detector drift. Experimental results will be provided that demonstrate near-background limited, 100 ns pulse detection performance given an 8.5 - 11.5 micrometer (300 K B.B.) radiant background, with the total noise floor spectrally white for optimal pulse averaging efficiency.

The atmospheric infrared sounder (AIRS) is a high resolution IR spectrometer (lambda/(Delta) (lambda) congruent 1200) which will map global temperatures and identify atmospheric aerosols from orbit by monitoring key atmospheric absorption lines. The focal plane consists of ten bilinear photovoltaic (PV) and two photoconductive (PC) HgCdTe detector arrays (modules) sampling a 3.7 to 15.4 micrometer spectral window in 15 bands. To attain the desired temperature accuracy, tight constraints on focal plane performance parameters such as linearity better than 0.1%, quantum efficiency (QE) on the order of 70%, low noise or noise equivalent quantum flux density (NEQFD), and no outages at key spectral lines have been imposed. Assessment of focal plane performance begins at the detector and readout levels where flight candidate detector arrays and CMOS readouts are selected. PV detector arrays and their readouts are hybridized (PC modules are wire-bonded directly) into modules which are then individually tested under simulated flight conditions. Five of the twelve module types are incorporated into an engineering-level (EM) focal plane upon which the module level tests are repeated as a prelude to the fabrication and testing of a separate, fully populated, flight-level (PFM) focal plane. Module testing has demonstrated that many difficult system requirements have been met, and work continues to optimize module performance. Lockheed Martin IR Imaging Systems' (LMIRIS) overall design of the infrared (IR) detector/Dewar assembly and focal plane development program is given, followed by a summary of PV and PC module data.

The atmospheric infrared sounder (AIRS) is being developed for the NASA Earth Observing System (EOS) program with a scheduled launch on the first post meridian (PM-1) platform in the year 2000. AIRS is designed to provide both new and more accurate data about the atmosphere, land and oceans for application to climate studies and weather prediction. Among the important parameters to be derived from AIRS observations are atmospheric temperature profiles with an average accuracy of 1 K in 1 kilometer (km) layers in the troposphere and surface temperatures with an average accuracy of 0.5 K. The AIRS measurement technique is based on very sensitive passive infrared remote sensing using a precisely calibrated, high spectral resolution grating spectrometer operating in the 3.7 micrometer - 15.4 micrometer region. The instrument utilizes a cryogenically cooled infrared spectrometer that uses a pair of pulse tube cryocoolers operating at 55 K to cool the HgCdTe focal plane detectors to 58 K. The instrument also has cryoradiators operating at 190 K and 150 K to cool the spectrometers' optical bench to 155 K. The cryocooler system is a highly integrated part of the AIRS instrument development whose design is focused to maximize the overall performance of the instrument. This paper provides a brief description of the AIRS instrument design and focuses on the results achieved to date on the development and integration of the pulse tube cryocoolers into this demanding instrument. In particular, the paper describes the cooler cryogenic and the overall thermal performance of the cryocooler. The thermal characteristics of the cooler system with the cold link coupling assembly also are presented.

This paper extends the previously reported results of cryogenic optical testing (SPIE Volume 2543, 1995) by including the results of further reduction of the test data for the 170-mm-diameter silicon carbide mirror and the 178-mm- diameter aluminum mirror. Both mirrors were manufactured by the Vavilov State Optical Institute, St. Petersburg, Russia, for infrared applications and were loaned to LMMS for these tests. Optical tests were performed in the Lockheed Martin cryogenic optical test facility at liquid helium temperatures, using a Zygo Mark II interferometer. The initial surface figures were 0.18 waves and 0.08 waves for the aluminum and the SiC mirrors, respectively, with figure error being given as rms wavefront error at 0.6328-micron wavelength at room temperature. It was found that the maximum change in shape after cooling was between 0.007 and 0.036 waves for the SiC mirror and between 0.017 and 0.062 waves for the aluminum mirror.

IASI is an infrared atmospheric sounding interferometer devoted to the operational meteorology and to atmospheric studies and is to be installed on board the ESA/EUMETSAT Polar Platform METOP to be launched in 2002. The required operating lifetime is 5 years. SAGEM/SAT has been developing the cold acquisition unit since 1991. The B-phase study was dedicated to the manufacture of the critical components, among which the IR detectors, optics, cold links and packaging. They concern the 3 types of detectors (InSb, HgCdTe-photovoltaic, HgCdTe- photoconductive) and the assembly technologies. The quantum detectors operate in the IR spectrum, so they are cooled at 100 K. The large spectrum (3.4 to 15.5 micrometer) is divided into 3 spectral bands. After manufacturing of these components, a program of test has been conducted and is reported for the evaluation of the technologies. It shows how the detector focal planes can sustain the space environmental conditions of an operational mission. It comprises two main files of test, mechanical evaluation and electrical evaluation. The detector environment has also been considered with aging and radiation tests, performed successfully. The B- phase is now achieved and all these development and testing activities are here reported.

Since 1986 there is a cooperation between NASA and DARA, Germany's space agency, to develop a flying telescope three times the size and ten times the light gathering ability of its predecessor -- the Kuiper Airborne Observatory. This project is called SOFIA -- Stratospheric Observatory for Infrared Astronomy. The 2.5 meter telescope for the visible through the infrared and the sub-millimeter wavelengths to the microwaves will be mounted in a modified Boeing 747-SP with a cavity at the port side behind the wings. It can be opened at stratospheric altitudes of around 41,000 feet, above 99.9 percent of the interfering water vapor. When not in use, the telescope will be sheltered from environment by a door in the fuselage. Vibrations of the aircraft would spoil the telescope's images. Therefore the telescope has to be isolated from the aircraft's structure. One promising solution for the rotational uncoupling is a segmented spherical air bearing with a bearing sphere diameter of 1.2 meter, which carries the telescope on a thin air cushion. In this paper a new technology of air bearings with micro nozzles manufactured with the aid of a laser is presented. The innovation is rooted in the unique combination of excellent static and dynamic characteristics. These types of air bearings were developed at the Lehrstuhl fur Feingeratebau und Mikrotechnik at the Technical University of Munich, and they are produced in series by the AeroLas GmbH, Munich.

By considering a one-dimensional cross-section through the rough surface, we derive a purely geometrical constraint on the statistical distribution of shadowed facet slopes that should be satisfied by any model of surface emissivity that includes the effect of self-shadowing. Our purpose is not to develop a single shadowing model, but to provide a condition that any valid shadowing model should satisfy. Although the emphasis of the presentation is theoretical, some practical ramifications also are discussed.

Cryocooler vibrational stability is an important issue in IR sensing. Unfortunately, several common approaches to this problem require that the cryocooler transfer function be accurately measured. We present a digital solution using a simple iterative algorithm for an axially aligned dual-piston cooler. We derived a formula for this algorithm to predict the vibration force attenuation A_k equals [1 - (mu) (cos(phi) + j sin(phi) )/1 + (epsilon) ]^k where k is the algorithm iteration number, (mu) is an algorithm parameter, (phi) is the maximum absolute error in the measured transfer function phase, and (epsilon) is the relative error in measured transfer function gain. If (mu) is chosen so that 0 less than (mu) less than 2 (1 + (epsilon) ) cos(phi) , the algorithm will provide an exponential vibration attenuation. As long as (phi) less than (pi) /2, it is possible to find a value for (mu) so the algorithm will converge. To demonstrate this property of the algorithm, we constructed a cryocooler vibration model using two large axially-mounted audio speakers mounted on a rigid structure with numerous vibration modes. Speakers were driven using 2 D/A channels and vibration forces were measured using an A/D and an accelerometer mounted on the structure. After accurately measuring the vibration response transfer function of the model, we corrupted phase angles between -(pi) /2 and (pi) /2. In each corrupted transfer function case, the control algorithm quickly converged to greater than 25 db below uncompensated vibration power and within 5 db of the static model vibration floor. Tests were then conducted on a Hughes 65K SSC cryocooler. The algorithm was able to significantly reduce vibrations and remain stable under a variety of changing operation parameters and cooling loads.

This paper deals with quantification of a two-dimensional (2- D) sampling process by pixel array. The idea is based on transformation of the Wigner-Seitz cell, which defines the sampling lattice in the spatial domain, into a 'bandwidth cell' in the spatial frequency domain. The area of the bandwidth cell is a quantitative measure of the sampling process. On this basis a description of the oversampling process is developed. We compare different configurations of the sampling pixel array.

The wide-field infrared explorer (WIRE) is a small spaceborne cryogenic telescope specifically designed to study the evolution of starburst galaxies. The use of advanced, large format, infrared hybrid focal plane array technology provides a large sensitivity gain over previously flown missions. The hybrid focal plane arrays (HFPAs) used in this instrument are 128 by 128-element arsenic-doped-silicon blocked impurity band infrared detector arrays connected via indium column interconnects to matching cryogenic multiplexers. The WIRE instrument includes two focal plane mount assemblies (FPMAs), each of which includes a HFPA optimized for a particular wavelength band. Details concerning design, fabrication and performance of the critical components of the WIRE FPMAs are described.

We are developing Germanium Blocked Impurity Band (BIB) detectors using Liquid Phase Epitaxy (LPE) to grow the high purity blocking layer and the heavily doped infrared absorbing layer. The properties of both epilayers require very low structural and electrical defect concentrations. To achieve these stringent demands, we have developed a high purity LPE process which can be used for the growth of high purity as well as purely doped Ge epilayers. We chose a low melting point, high purity metal with negligible solubility in Ge as a solvent. A good candidate is Pb, a group IV element with a solubility <1017 cm3 at 650°C which does not form electronic levels in the band gap of Ge. The Ge single crystal substrates are optically polished and orientated -4-2° away from (111). The first tests with BIB structures with just the purely doped absorbing layer grown on high purity substrates with LPE look very promising. The detectors exhibit extended wavelength cutoffwhen compared to standard Ge:Ga photoconductors (165 m vs. 120 rim) and show the expected asymmetric currentvoltage dependencies. Future work on these devices will include optimizing doping, dark current, layer thickness, absolute responsivity, Noise Equivalent Power (NEP), and even longer wavelength cutoff as well as an indepth understanding of how the parameters are interrelated. Keywords: Germanium, Far Infrared Detectors, Epitaxy

Traditionally, photoconductive (PC) HgCdTe detectors have been used in interferometers for detection in the 14-15 .tm range. In this paper we present recent quantum efficiency and junction impedance data which demonstrate that P-on-n HgCdTe photovoltaic (PV) detectors with 16-17 m cutoff wavelengths at 70 K are suitable for use in spaceborne remote sensing interferometrjc instruments such as IMG-2, ATRAS, TES and CCOSM. Theperformance of these large-area detectors is of particular importance for interferometers because they have higher linearity at higher fluxes than PCHgCdTe arrays. The linearity requirement of 1% for the IMG-2 instrument, with background fluxes in excess of 1016 ph/cm2-s, is only marginally met by PC HgCdTe detectors. We present, for the first time, data showing better than 1% linearity at fluxes of l.3x10'7phlcm2-s for PV HgCdTe detectors with 60 K cutoff wavelengths of 15.5 pm. Keywords: HgCdTe, infrared detectors, photovoltaic detectors, linearity, interferometers,mercury cadmium telluride, IMG-2

High resolution infrared imaging system calls for very long scanning arrays with several thousands of detectors and high performance. This paper presents the recent technological developments and the electrooptical performances obtained at LETI I LIR (Infrared Laboratory) on 1500 detector linear HgCdTe arrays working in the 3-5 and 8-10 pm spectral ranges. These very large arrays (length 50 mm) have an indirect hybrid architecture composed of butted HgCdTe PV detection circuits and Si CMOS readouts hybridized on a mechanically close-matched fanout substrate. Defect free dicing and butting, respecting the detector pitch, is made by accurate and non damaging techniques. Keywords: Infrared, HgCdTe, linear array, butting, focal plane array

Probably the most important factor in producing HgCdTe detectors of high performance is surface passivation. A good passivant for PC HgCdTe detectors accumulates the surface thereby reflecting minority carriers from surface imperfections and increasing minority carrier lifetime. A variety of passivants are known and used to various degrees, including sulfides, fluorides, oxides, and others. One of the problems with known passivants is that they tend to accumulate the surface too strongly, thus producing non-optimal results. We have developed a new passivation process which passivates the surface without strong accumulation. This results in detector resistance that is about 50%higher than that achieved with traditional KOH passivation, responsivities that are from 100 to 200% higher, and detectivities that are from 50to 100% higher for long wavelength devices. Materials and processing details used to achieve these results, as well as experimental data will be presented. Keyword: passivation, infrared, HgCdTe, detector

In this work the design and performance of a 537 (H) x505 (V) -element PtSi Schottky-barrier diode (SBD) IRCCD are described. To downsize the JR camera, the pixel size of the IRCCD has been reduced to 15.2mx11.8jtm. The package size of the IRCCD is l4mmxl4mm. The reduction of the pixel size causes a decrease in thermal sensitivity. However, the noise equivalent temperature difference (NETD) of the IRCCD is less than 0.13°C, because the transfer conversion gain from the electrons to the voltage has been increased, by decreasing the capacitance of its FDA. Furthermore, the NETD can be decreased to 0.1 1°C by increasing the platinum deposition temperature to 340°C. The IRCCD has an electrical shutter function with which the exposure time can be varied from 1/500 second to 1/5000 second. In addition, the IRCCD has a mixed-signal-mode shutter function, which was developed to expand the dynamic range. The mixed-signal-mode shutter function is performed by mixing the signal electrons of two kinds of pixels, one shuttered and the other unshuttered. The IRCCD also has a temperature monitor diode on a chip to control the cooling system of the JR camera. However, inclusion of this diode causes an increase in the fixed pattern noise. To reduce this noise, the monitor diode is forward biased for only a moment for temperature measurement. Keywords: PtSi SBD IRCCD, downsizing, electrical shutter, temperature monitor diode

For different applications the use of uncooled thermal infrared detectors is often a low-cost alternative to the cooled semiconductor detectors. By the development of a large number of novel detector technologies the thermal and spatial resolution ofthe thermal detectors could be improved considerably. On the basis of the pyroelectric material lithium tantalate (LiTaO3) a cheap and flexible detector technology was developed for the design and manufacturing of user-specific arrays even at small batch quantities. The possibilities of this technology are described by the example of newly developed linear arrays with 128 responsive elements of different sizes (pitch 100 i.tm) and 256 responsive elements (pitch 50 jtm) as well as a two-dimensional array with 16 x 8 responsive elements. The given detector properties ofthe arrays clearly show that the achieved detector properties meet the demands of many applications. Responsive elements having a thickness of less than 5 jtm can be produced by the use of ion-beam etching for the stmcturing ofthe pyroelectric chips. In connection with a low-noise CMOS read-out circuit, NEP-values lower than 1 .5 nW were obtained by it at a chopping frequency of 128 Hz. The effective capacity of the detectors is illustrated on the basis of two detector applications in devices for the twodimensional temperature measurement and in a spectrometer. Keywords: infrared, uncooled detector, pyroelectric, array, manufacturing, properties, thermal imaging, spectrometer

The nucleation of CdTe onto basal plane sapphire and the subsequent growth of a CdTe buffer layer has been studied using in-situ laser reflectance (probe wavelength 633 nm, HeNe laser). The production of midwave infrared focal plane arrays requires the growth of typically 10 micrometer of CdTe (111)B buffer layer in order to grow out problems due to stacking faults, dislocation clusters and twinning. A-face and B-face growth of CdTe is seen to produce different reflectance 'signatures' within the first 6000 angstroms of growth, so enabling the early identification of problems with the growth process. Laser reflectance was also successfully demonstrated to predict the thickness of the buffer layer. Oscillations in the laser reflectance are attenuated due to absorption by the film at the probe wavelength used after approximately 6000 angstrom. However by the on-line calculation of the growth rate at every half wavelength oscillation, it is possible to extrapolate a film thickness for the total growth time. This extrapolated value is seen to be in good agreement with the thickness calculated ex-situ by beta-back scattering. The dependence on the buffer layer growth on the nucleation conditions was also investigated. The determination of whether the buffer layer grows A-face or B-face is seen to be more influenced by the II:VI ratio than the temperature during nucleation. For a nucleation temperature of 400 degrees Celsius, with a II:VI ratio of 6:1 the growth of the buffer layer is seen to be 100% A-face. As the II:VI ratio is increased the degree of A-face growth is seen to decline and the material becomes dominated by B-face growth. At a II:VI ratio of 60:1 the material is entirely B-face and predominantly untwinned. The difference in the two growth modes is manifested in the laser reflectance. Greater scattering of the laser light occurs during B-face growth due to the increased roughening compared to A-face growth. Consequently the reflectance signal in the B-face signature is seen to fall away more rapidly than is the case with A-face growth.

The contribution of the series resistance and contact resistance has been taken into account while working out the relation between zero bias resistance-area product and perimeter-to-area ratio of the diodes in variable area diode test structures. The effect of these resistances on the interpretation of the results from the variable area array experiment in HgCdTe test structures is discussed. The analysis of the experimental data to explain some of the past unexplained observations is presented.

Lead-sulphide films were deposited on glass substrates by XeCl(308 nm) excimer laser ablation of lead target in H₂S ambient gas. Series of pulses at the repetition rate of 1 HZ were directed to the target surface. The pulse energy was set at about 200 mJ/pulse. Pulse duration was about 60 ns. The deposited films were characterized by absorption spectroscopy, scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS).

Surface forest fires (SFF) is the most common natural type of the forest fire causing a great ecological and economic damage. Although quite a lot of experimental works have been devoted to an investigation of SFF, a problem of a dominating mechanism of transferring energy from the zone of reaction to a forest fuel has not been solved yet. Exact profiles of the combustion product concentrations in the fire front are not known, and limiting conditions of its spread have not been properly investigated. To detect forest fires passive optico- electronic systems located on space apparatus are coming into use. However, to estimate the efficiency of space techniques, identification methods, classification and prediction of the forest fire development it is necessary to know thermal flows in the assigned spectral intervals, attenuation of an irradiation by an atmosphere, by particles of smoke and crowns of the trees, efficient combustion areas depending on the type of the fire and some other characteristics. Besides, it is necessary to take into account that a combustion process of the forest fuels depends on their density, moisture content, initial temperature and humidity of the air as well, speed and direction of the wind, the angle of terrain relief slope. Investigation of SFF in the natural, large scale experiments is complicated because of the bad reproduction of the results and considerable dependence of the combustion parameters on external factors. In general this problem is solved by means of laboratory devices which allow to model partly the conditions of the surface forest fire initiation and spread. For example, in the works set-ups for physical modeling SFF in specialized aerodynamic pipes are described. However, this method has unavoidable drawback caused by the fact that a real process of the forest fuel combustion in an open space is modeled by a combustion of the forest fuel in a half-closed space where the experiments are made. Closeness of the space in specialized aerodynamic pipes results in a change of temperature and composition of the medium and influences velocity fields of the fire front as a result of the traction force change in the area of SFF. Hoover, experimental works on investigation of the fires in laboratory conditions continue, new laboratory set-ups being made allowing to exceed the range of investigating forest fuel combustion with more exact approximation to the real conditions. In contrast to the natural investigations laboratory experiments can be carried out all the year round with less material expenses.3122

The problems of working out the IR-CW-LFM-lidar with transformation of one frequency laser radiation into two frequency and tuning probability are considered. Comparative analysis results for characteristics of two frequency laser radiators put into differential IR-CW- LFM-lidars are given. The perspectivity for amplitude-phase electrooptical devices developmeni is shown. Their scheme decisions are considered. Theoretical and experimental investigation results of transformation parameters effect on purity of radiator output spectrum, as the main function, which determines the metrological characteristics of IR-CW-LFM-lidar on the whole are presented. The possibilities of IR-CW-LFM-lidars with frequency transformation realizing different ways of gas remote sensing are estimated. The experimental setup's structural scheme is presented. Keywords: remote sensing, infrared lidar, linear frequency modulation, electrooptical frequency transformation

A hybrid structure, including an isotypic p-lnP-p-In_0.53Ga_0.47As heterojunction and a Pd-p-InP diode, is grown. The current-voltage and capacity-voltage characteristics, the spectral photosensitivity, and the dependence of the photocurrent on bias and magnetic field are investigated. It is shown that photosensitivity is virtually the same at the two main maxima and constitutes I_ph equals 6*10^-2 A/W for (lambda) _max equals 0.90 micrometer and I_ph equals (2-4)* 10^-2 A/W for (lambda) _max equals 1.55 micrometer. The photo-emf at (lambda) equals 0.90 micrometer under the influence of the gas mixture air +500 ppm H₂ increases by factor 10. This increase is virtually instantaneous, the drop-off reaches -3 min. The current transport mechanism is investigated and the explanation of variation of photo-emf (photocurrent), and dark current in H₂-atmosphere are presented. Such a hybrid structure is of practical interest for detecting both hydrogen and radiation in the near-IR region of the spectrum. Different types of n(p)-InGaAs diode structures have been an object of multifaceted investigations for a number of years, especially in connection with their possible extensive practical applications. Technical developments have been directed primarily toward optimizing the constriction of p-i-n structures, Schottky diodes, avalanche photodiodes, and heterojunctions for fast photodetectors in the wavelength range 1.3 - 1.6 micrometer. The problem of producing detectors for hydrogen gas and hydrogen-containing gases has occupied a prominent spot for a number of years among possible practical applications of semiconductor diode structures. Among our own published studies of this problem, we call attention to Ref. 7 concerning an InGaAs-based photodetector as hydrogen detector. In this communication we report the results of experimental studies of a hybrid structure based on an isotypic p-InP-p-ln_0.53Ga_0.47As heterojunction and a Schottky barrier formed by a palladium contact on p-InP.

Investigations of the performance of quantum well infrared photodetectors (QWIPs) as compared to other types of semiconductor infrared detectors are presented. Two types of QWIPs are considered: GaAs/A1GaAs intersubband quantum well photoconductors and type II staggered InAs/InGaSb photodiodes. In comparative studies the HgCdTe photoconductors and photodiodes, PbSnTe photodiodes, Schottky barrier photoemissive detectors and doped silicon detectors are considered. HgCdTe photodiodes indicate better performance in comparison with GaAs/A1GaAs QWIPs operated in the range 35to 77 K. The cooling requirements for GaAs/A1GaAs QWIPs with cutoff wavelengths below 10 tm are less stringent in comparison with extrinsic detectors and Schottky barrier devices. The theoretically predicted performance of long wavelength InAs/GaInSb photodiodes are comparable with HgCdTe photodiodes. Keywords: infrared photodetectors, HgCdTe photodiodes, GaAs/AlGaAs photodetectors, quantum well InAs/GaInSb photodiodes.

The simulated interferometric patterns of the primary aberrations obtained with two rotationally sheared wavefronts are presented. The shearing angle is seen to control the number of fringes in the interferometric pattern. For small shearing angles, the phase difference in the argument of the cosine function reduces to the derivative of the wavefront multiplied by the shearing angle.

A simple and elegant method to determine unambiguously the phase from several phase-shifted interferograms (intensity fringe patterns) is presented. Instead of calculating the arc- tangent, a line integral of the phase gradient is evaluated. The ambiguities introduced due to the multiple values of the arc-tangent function are avoided, eliminating the necessity for the complex methods of phase unwrapping. This method works effectively even in the regions of high intensity gradients, is insensitive to the profile of the illuminating beam and to the shape of the domain boundaries. The algorithm is applied to the special case of four phase-shifted interferograms to demonstrate the phase determination procedure.

The Geostationary Earth Radiation Budget (GERB) instrument is to be flown on ESA's Meteosat Second Generation (MSG) satellite in 2000. The purpose of the instrument is to measure accurately the daily cycle of the reflected and emitted radiation of the Earth over at least a five year period. The measurements will be made from geostationary orbit and will complement those planned from instruments in low Earth polar orbits. The data from GERB will provide the first consistent measurements of the hour-by-hour variation of clouds and simultaneous measurements of the radiation balance, and will allow climate models to be further developed and validated. The instrument will accumulate images of the Earth disc every 15 minutes in wavebands of 0.32 - 4.0 pm and 0.32 - 30 im with a nadir resolution of 50 km. The detector for this instrument consists of a 256 pixel linear array of thermoelectric (TE) elements. The TB array operates at room temperature and is blacked to give a flat spectral response over the 0.32 - 30 im band. The detector hybrid consists of the 256pixel detector plus 4 Application Specific Integrated Circuits (ASICs), comprising 64 channels each, which perform front end analogue signal processing, A/D conversion and multiplexing. As the MSG platform is spin-stabilised, the Earth image is stabilised on the detector using a de-spin mirror and is only present on the detector for 40 ms. Integration of the signal over the 40 ms and taken over a 15 minute observation period enables the radiance in both long and short wavebands to be measured to an accuracy better than 1%. The detector concept is described and test results of a prototype system are presented. Keywords: JR detectors, thermoelectric, gold black, EOS

Modeling the optical response of grating profiled PtSi/Si structures is examined to demonstrate the potential of microstructuring in optimizing the absorption of infrared detectors. Coupling to angularly broad surface plasmon polariton resonances near normal incidence is, in fact, achieved at both Si/PtSi and SiO₂/PtSi interfaces for the same grating parameters in the wavelength ranges 3.0 - 4.4 micrometer and 1.3 - 1.9 micrometer respectively. These ranges correspond to two infrared, atmospheric transmission windows, and demonstrate the potential for a single device geometry to operate optimally in two different spectral bands. It is also shown that, throughout these spectral bands, it is possible to attain reflectance significantly lower than that of the planar structure counterparts in the angle range 0 degrees to plus or minus 20 degrees (corresponding to the use of F1.4 optics), along with containment of low reflectance to that angle range. Absorption mediated by the PtSi/Si surface plasmon polariton mode may be of particular interest in these Schottky barrier structures, since there would be considerable enhancement in the generation of hot carriers in the near barrier region where they have a better chance of direct or indirect (via elastic scattering) promotion over the barrier to give rise to a detectable charge.

It is given the general picture of transient processes in low- background IR detectors under variable extrinsic irradiation, is shown how this picture is exhibited in the operation of these devices and how their problems can be solved. Special attention is given to the effect of the detector contacts on the performance of the devices and optimization of their operation.

Cadmium mercury telluride (Hg_1-xCd_xTe or MCT) non- equilibrium detector structures which allow room temperature operation have been grown by metal-organic vapor phase epitaxy (MOVPE). These devices suppress the auger generation by reducing the intrinsic electron and hole concentrations in the active region of the device. The MCT characteristics in this region should then be determined by the extrinsic doping concentration. In order to minimize the remaining generation processes within this so called (pi) -region, it is best formed from low acceptor doped (low X10¹⁵ cm^-3) MCT, with as low a trap density as possible. The p⁺(pi) n⁺ device structure which is required to achieve the non-equilibrium phenomena requires stringent control on acceptor and donor doping, as well as composition. Acceptor doping studies with trisdimethylamino arsine (DMAAs) have been performed using GaAs and CdZnTe substrates. Minority carrier lifetime results have been obtained which are near rotatively limited and comparable to As-doped, Hg-rich liquid phase epitaxy (LPE) grown layers on CdZnTe substrates. Ambient temperature, auger-suppressed devices have levels of 1/f noise which currently limit their use in imaging applications. However, they are of great interest in other applications such as approximately equals 10 micrometer negative luminescence emitter devices and heterodyne detection of 10.6 micrometer infrared (IR) radiation from carbon-dioxide lasers. Reduction in the series resistances has been achieved by utilizing a device design with a n⁺ MCT common which should improve the frequency response of these devices. Another design modification, predicted to reduce the leakage current, has been the introduction of low doped, wide band gap regions either side of the (pi) -region. In practice these structures have produced over an order of magnitude improvement in the leakage current characteristics.

A new method to determine unambiguously the phase from several phase-shifted interferograms (intensity fringe patterns) has recently been demonstrated. This method is applied to very noisy interferograms, specifically to the case of four phase- shifted interferograms, to demonstrate the phase determination procedure.

The temperature dependence of the detected incidence of thermal radiation in a wavelength interval is evaluated for a quantum and thermal detector. In both cases, the temperature dependence of emissivity is considered a contributing factor.