Abstract: A Compressing Capacitively Coupled Transimpedance Amplifier (CCTIA) circuit (10) has an amplifier (AMP) with a variable capacitance feedback network (C1, C2, C3, Q1, Q2) coupled between a current receiving amplifier input node and an amplifier output node. The output node outputs a voltage in response to a received current. The variable capacitance feedback network is responsive to the output voltage for establishing one of a plurality of different transimpedance values for the circuit such that the circuit exhibits a greatest transimpedance value for an input current having a magnitude below a threshold magnitude, and a lesser transimpedance value for an input current having a magnitude equal to or above the threshold magnitude.

Abstract: A hinge (20) includes two hinge plates (22, 24) and a connecting hinge pin (32). A coil spring (48) supported on a bushing (44) overlies the hinge pin (32), which is free to move along its longitudinal axis (30). A cam follower (42) on the hinge pin (32) engages a cam (32) mounted to one of the hinge plates (22), so that the hinge pin (32) slides longitudinally as the hinge plates (22, 24) pivot relative to each other about the hinge pin (32). As the hinge pin (32) slides longitudinally, it axially compresses or decompresses the spring (48). The cam (32) is oriented such that pivoting of the hinge plates (22, 24) in either direction from an open position compresses the spring (48), providing a restoring force which tends to retain the hinge plates (22, 24) in the open position.

Abstract: A lower vacuum housing (34) of a sensor dewar (26) is fabricated in a single brazing operation from ceramic and metallic components. The components are assembled with ceramic-to-metal interfaces and metal-to-metal interfaces. Brazing is accomplished by active brazing of the ceramic-to-metal interfaces and non-active brazing of the metal-to-metal interfaces. Specific combinations of active braze alloys and non-active braze alloys are provided for various combinations of dewar materials.

Abstract: A feedthrough (34) is formed of a feedthrough plate (44) having at least one bore (46) therethrough and a feedthrough pin (48) hermetically sealed into the bore (46). The feedthrough pin (48) includes an elongated pin (50) having an axis of elongation (52), a recess (54) in at least one end of the pin (50), the recess (54) extending parallel to the axis of elongation (52), and a gold coating (56) within the recess (54). There are preferably a plurality of bores (46) in the feedthrough plate (48) and a corresponding plurality of the feedthrough pins (48). The gold coatings (56) at the ends of the feedthrough pins (48) are desirably lapped to ensure coplanarity and a smooth surface finish especially suited for wire bonding or tab bonding.

Abstract: A light source radiates an infrared beam that passes through a chopper, a calibration cell and the exhaust plume of a motor vehicle passing in front of the source. A photosensor assembly includes a plurality of photodetectors which are spaced closely adjacent to each other and simultaneously sense the beam after it propagates through the plume. An optical beam homogenizer or integrator disposed between the plume and the photosensor unit causes the light incident on the photodetectors to have uniform intensity. The photodetectors are sensitive to different wavelengths corresponding to spectral absorption peaks of constituents of the composition of the plume, including carbon monoxide (CO), carbon dioxide (CO.sub.2), hydrocarbon (HC), water vapor (H.sub.2 O) and nitric oxide (NO). A computer computes the composition of the plume as the percentages of the constituents based on the sensed transmittances of the respective wavelengths through the plume.

Abstract: An array of dual-band HgCdTe radiation detectors (10) wherein individual detectors include a first layer (14) having a first type of electrical conductivity and a bandgap selected for absorbing radiation within a first spectral band. The radiation detectors also each include a second layer (16) overlying the first layer. The second layer has a second type of electrical conductivity that is opposite the first type of electrical conductivity. Each radiation detector further includes a third layer (18) overlying the second layer, the third layer having the first type of electrical conductivity and a bandgap selected for absorbing radiation within a second spectral band. The first and second spectral bands are selected from SWIR, MWIR, LWIR, and VLWIR. The first, second and third layers are contained within at least one mesa structure (10a, 10b) that supports on a top surface thereof a first electrical contact (24) to the first layer and a second electrical contact (28) to the third layer.

Abstract: A system for receiving electromagnetic energy with reduced signal aliasing in the cross-scan direction. The system is adapted to be mounted on a spacecraft or an aircraft for movement over a surface in the cross-scan direction and has a sensor for receiving electromagnetic energy. The invention (10) includes an arrangement for directing energy to the sensor which has an astigmatic blur in the cross-scan direction which is effective to reduce aliasing of a signal transmitted or received by the system in the cross-scan direction of movement. In the illustrative embodiment, the invention (10) includes an array (20) of radiometric detectors. A reflective optical arrangement directs energy from a surface to the detector array. The optical arrangement includes at least one mirror (16) which has a small controlled cylindrical surface perturbation which introduces an astigmatic blur into the received image which reduces aliasing of the signal in the cross-scan direction.

Abstract: A photovoltaic diode unit cell (10) includes a first layer (14) having a first type of electrical conductivity and a second layer (16) of Group II-VI material having a second type of electrical conductivity that differs from the first type. The first layer and the second layer are coupled together so as to form a photovoltaic junction (15) therebetween. The photovoltaic junction is coupled via electrical interconnects (18, 20, 22) to a readout 24 and collects first charge carriers resulting from an absorption of IR radiation within the layer 14. The junction also collects second charge carriers resulting from the absorption of visible light in a region of highly graded crystal potential formed, in a Liquid Phase Epitaxy (LPE)-grown embodiment of this invention, at an interface of a substrate and the first layer. The substrate is subsequently removed, preferably by a mechanical operation followed by a wet chemical etch, to expose the region of highly graded crystal potential.

Abstract: An adaptive dynamic range control circuit architecture is disclosed that enables an IR-FPA (10) to achieve a higher dynamic range. The circuit architecture significantly reduces a resolution required for an analog-to-digital converter (ADC 24) that converts the analog output signals of the IR-FPA to a digital representation. In a preferred embodiment of this invention a column CTIA readout integrated circuit architecture is used in conjunction with the adaptive feedback circuitry of this invention to provide pedestal suppression on a per-pixel basis for the IR-FPA. The use of the circuitry of this invention modifies the conventional column CTIA amplifier configuration to a configuration having an auto-zeroed charge ratioed gain stage (50). One advantage to this technique is that by suppressing the charge pedestal, the usable signal output from the IR-FPA can be brought off-chip to the readout integrated circuit at a much higher gain.

Abstract: A single integrated source of infrared and ultraviolet energy with minimal visible radiation therein. The invention (10) includes a first source of infrared and visible radiation (12) and a second source of ultraviolet and visible radiation (14). In a specific implementation, visible radiation from the infrared source (12) is eliminated by a filter (20) comprising a germanium substrate coated with a thin film multilayer stack. The filtered infrared beam and the ultraviolet beam are combined by a set of mirrors. A cold first mirror (30) directs the ultraviolet energy to a cold second mirror (22) which then transmits infrared energy and reflects ultraviolet energy. The visible radiation from the ultraviolet source is eliminated by transmission through the first cold mirror. The first and second mirrors provide a composite output beam which is collimated by a third mirror (36) and output as a single beam. For safety, a shutter (24) is provided in front of the ultraviolet source (14).

Abstract: Two dichroic mirrors (26, 30) and a dichroic beamsplitter (36) are introduced into the conventional Michelson Fourier transform spectrometer to accommodate two spectral bands. A conventional Michelson Fourier transform spectrometer (FTS) uses two mirrors (20, 22), one fixed (20) and the other moving (22). The present invention replaces each of the two mirrors (20, 22) with a pair of mirrors, one of which is a dichroic mirror (26, 30). The present invention involves inserting the first dichroic mirror (26) fixed in position between the beamsplitter (12) and the first plane mirror (20) and inserting a second dichroic minor (30), which can be moved in a direction normal to the plane surface, between the beamsplitter (12) and the second plane mirror (22). The first dichroic mirror (26) and second dichroic mirror (30) transmit long wavelength radiation and reflect short wavelength radiation.

Abstract: A radiation detector (1) unit cell (10) includes an n-p+ LWIR photodiode that is vertically integrated with a p+-n MWIR photodiode in a n-p+-n structure. Electrical contact is made separately to each of these layers in order to simultaneously detect both the LWIR and MWIR bands. The electrical contact is made via indium bump interconnections (23, 25, 27) enabling the unit cell to be subsequently hybridized with a topside mounted electronic readout integrated circuit (30). The n-p+-n structure in a given pixel of an array of radiation detector pixels is electrically isolated from all neighboring pixels by a trench (28) that is etched into an underlying substrate (12). To compensate for a reduction in the optically sensitive area due to the placement of the electrical contacts and the presence of the pixel isolation trench, a microlens (34) may be provided within, upon, or adjacent to the backside, radiation receiving surface of the substrate in registration with the unit cell.

Abstract: A method and apparatus are provided to eliminate spectral interference variation contained in optical signals transmitted to an optical detector or array of optical detectors, the spectral variation deriving from the presence of a layer deposited on the detector having a different index of refraction from the detector. The practice of the invention involves optically coupling a plate to the layer using an adhesive, with the proviso that the plate, layer and adhesive have substantially the same index of refraction so that a composite thickness with the refractive index of the layer is formed. Given the inverse relationship between thickness of the layer and period of the interference in wavenumber, the effective increase in thickness of the layer yields a corresponding decrease in the period.

Abstract: An in-situe chemical gas or fluid analyzer for vehicles, industrial, environmental and process control applications. As applied to a vehicle (1) having an internal combustion engine, the analyzer includes: (i) a source of electromagnetic radiation (14, 16); and (ii) a sampling cell (12) which collects emission gases of interest and which is capable of withstanding hostile environments while preserving a "clear" optical path between the sensor sampling cell and the source of radiation. The analyzer further includes: (iii) a solid state sensor (24, 26, 28, 30, 32 ) of monolithic construction which selectively detects electromagnetic radiation that is absorbed or emitted by one or more chemical species of interest, that compensates for temporal and spatial variations in illumination level provided by the source, and that provides an electrical signal output, in either analog or digital format, that is related to the measured concentrations.

Abstract: Optical immersion of a semiconductor photodetector to a plano-convex lens is obtained with a spring arranged to urge the photodetector to abut the lens. To facilitate alignment of the detector and the lens, the spring defines, in one embodiment, a convex surface to abut a substrate that carries the detector. In another embodiment, alignment is facilitated by a ball positioned between the spring and the substrate. Optical noise is reduced by a dielectric between the detector and the lens, with the dielectric thickness less than 1/10 of any radiation wavelength of interest.

Abstract: A method for fabricating a two layer epitaxial structure by a liquid phase epitaxy (LPE) process, the structure being comprised of a Group II-VI semiconductor material. The method includes the steps of providing an LPE growth chamber that contains a molten Group II-VI semiconductor material 24, the molten Group II-VI semiconductor material having a first temperature (T.sub.1); growing, at the first temperature, a base layer (22) from the molten Group II-VI semiconductor material, the base layer being grown to have a first bandgap energy; employing a shutter mechanism (30) to isolate the base layer from the molten Group II-VI semiconductor material without removing the base layer from the growth chamber; reducing the first temperature of the molten Group II-VI semiconductor material to a second temperature (T.sub.

Abstract: A focal plane array (10) of radiation detectors (10b) has all features inclined with respect to an illuminating beam of radiation. That is, all features that would be orthogonally disposed with respect to an incoming wavefront are instead inclined to the incoming wavefront, an arrangement referred to as compound tipping. The disclosed embodiments of the invention create a compound tipping of the focal plane array such that there are no features of the array, such as mesa edges and sidewalls, that lie in the plane of the incoming wavefront. As a result, only a small amount of scattered light is observed, and the optical signature is significantly reduced. The invention substantially eliminates the optical signature by simultaneously tipping the focal plane features (optically and/or mechanically) in both major array axes, without degrading the imaging performance of the detective assembly.

Abstract: Interior circuit card supports and a method that facilitate fast and simple Assembly and disassembly of the circuit cards, and provide both interior and peripheral card support, are disclosed. A plurality of circuit cards 32a-32n, each having at least one interior hole 36, are positioned substantially parallel to each other with the holes of the various cards collinear. A plurality of grommets 38 are secured in the holes, with each grommet providing a first coupling. A rod 42 having a plurality of second couplings 44 is inserted through the grommets such that the second couplings mate with the grommets' first couplings to provide an interior support that maintains the spacing between the circuit cards. In the preferred embodiment the grommets are internally threaded with a groove that extends their entire length, and the rod has deformable inserts that form an interference fit with the grommets' threads. The rod is inserted and then rotated, causing the inserts to deform and grip the threads.

Abstract: An ultra low power gain circuit (UGC) implements a unique operational mode of a source follower circuit, and enables programmable gains greater than unity. A MOSFET has a gate terminal coupled to an input capacitance (Cin). A potential at a drain of the MOSFET is clocked to enable charge to flow through the channel. This charge charges a capacitor (Cout) that is connected to a source of the MOSFET. After charging Cout, the drain potential is restored to an initial value, and the charge on Cout discharges back through the MOSFET until the source voltage is one threshold drop from the gate potential, at which time the MOSFET turns off. Cout then stops discharging, and the final voltage appearing on Cout is a function of the magnitude of the gate voltage appearing on Cin. As the voltage at the source of the MOSFET changes, capacitive coupling, via (Cgs) to the gate, causes the gate voltage to also change. The value of the gate voltage determines a magnitude of a final voltage to which the source settles.

Abstract: A compositionally graded HgCdTe radiation detector (10) is constructed to have a high purity "denuded zone" (Region 2) that is formed adjacent to a radiation absorbing region (Region 1). The compositional grading results in an internally generated electric field that is orthogonally disposed with respect to an externally generated electric field applied between contacts (16, 18). The internally generated electric field has the effect of injecting photogenerated minority charge carriers into the denuded zone, thereby reducing recombination with photogenerated majority charge carriers and increasing carrier lifetime. The detector further includes a wider bandgap surface passivation region (Region 3) that functions to trap, or "getter", impurities from the denuded zone and also to reduce surface recombination effects.