Detectors, Focal Plane Arrays, and Applications

Size restrictions of radiation detecting with semiconductor photodetectors

Evgenij A. Salkov, George S. Svechnikov, Nikolai M. Krolevets

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The article presents an analysis of problems which arise in thermal radiation detection by means of a photodetector when the photodetector and/or light source is of small size. Practical expediency of the analysis is linked with the problem of adequate identification of small objects which are observable within the spectral region of thermal radiation and, on the other hand, with lossless transmission and processing of optical information. Consequently, it is necessary to take into account the physical peculiarities of both detector and emitter to determine the real capabilities of the transmitting-detecting processes. Quantum limitations which stem from uncertainty relations (impulse-coordinate, energy-time and phase-photon number) and classic restrictions of mode number of thermal radiation within the cavity of a small fixed volume have been examined. Corrections are introduced in expressions for both the detectivity spectral dependence and noise equivalent temperature. These correspond to size-corrections to the spectral distribution of `small-blackbody' radiation. It is also shown that a light source of a small size drastically influences the time which is required to detect this light source, or an object which consists of small-size particles (porous, cloud-like objects etc.). The spectral `quality' of blackbody emission is discussed briefly in connection with heterodyne detection.

Characterization of infrared detectors for space applications

Didier Dantes

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Over the past decade, AEROSPATIALE has become Europe's leader in the field of optical payloads for space applications. This leadership was made possible by AEROSPATIALE's will to develop the assets required for mastering the key performances of optical payloads, i.e. geometrical, modulation transfer function, radiometric and spectral performances. Infrared detectors have a heavy weigh in the performances of infrared payloads, and this leaded AEROSPATIALE to perform very accurate characterization of infrared detectors. This paper looks at those figures of merit of infrared detectors which are of interest to optical payload's performances. These parameters are detector sensitivity and associated dispersions, temporal noise and associated dispersions, contributors to spatial noise (pixel to pixel variation of non linearity, spectral response, 1/f noise, dark level variation versus temperature,...), frequency response, modulation transfer function, geometrical detector performances. The techniques required for detector characterizations compliant with the required accuracies for each of these parameters are described. Performances of test benches available at AEROSPATIALE are presented, with associated performances: vacuum chambers and cooling test sets, optical sources for radiometric and MTF measurements, electronics for detector power supply, clock generation, video and image processing.

Uncooled multispectral detectors and their applications

Volkmar Norkus, Guenter Hofmann, Christian Schiewe

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The article describes the basic design and essential properties of developed multispectral detectors. The presented detector concept on the basis of lithium tantalate (LiTaO₃), a pyroelectric material, makes the parallel measurement possible in four spectral channels in the wavelength range of typically 1 - 25 micrometers . The detector consists of an optical unit with the beam splitter and interference filters for the spatial and spectral dispersion of the incident total radiation and the responsive elements with appropriate low-noise preamplifiers. The detector is a discrete and compact component in a TO 8 transistor casing (empty set 14 mm X 10 mm) with an aperture of typically empty set 2 mm. Essential properties of a four-channel detector for the gas analysis (CO; CO₂; HC; REF) are described and the influence of the beam splitter geometry on the overlap of the measuring spots in the spectral channels is discussed. As a detector application a novel multichannel pyrometer is presented by means of which the influence of the object emissivity on the measuring accuracy has been reduced considerably.

Second-generation infrared detectors: present situation and prospects in France

Daniel Amingual, Francis Bertrand

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This paper presents the state of the art of second generation cooled and uncooled infrared detector technologies. Indications concerning the situation of the market and the industry are given. Future prospects are geared to a double approach: increasing performances and cost reduction. We present the main technological actions at Laboratoire Infrarouge to achieve these goals.

Collective flip-chip technology for HgCdTe IRFPA

Jean-Luc Tissot, Francois Marion

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After a description of the flip-chip techniques developed at LETI, we present its main advantages and its evolution. Using this basic method, a mass production procedure has been developed in order to decrease the cost of the technological step. With this new method, we are able to simultaneously hybridize several linear or 2D arrays directly onto readout circuits on empty set 100 mm silicon wafer. The electrical accessibility to the components provided by the method enables more detailed electrical tests to be carried out with an automatic prober before manual integration in cryogenic conditions which is done only for good electrical devices. We have also developed a high reliability method in order to hybridize very large IRFPA. With this improved technique, 256 X 256 arrays can undergo several thousand 300 K - 77 K cycles without degradation.

Complete range of lightweight cryocoolers for integrated Dewar assembly (IDA)

Patrick Curlier

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Abstract not available.

HgCdTe detector technology at Kunming Institute of Physics

Junhong Su, Gehong Zeng

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HgCdTe detector and thermal image system laboratories at Kunming Institute of Physics have been carrying the research and development of HgCdTe detectors and thermal imaging systems for a wide range applications for over 20 years. During this period, significant progress has been made in many areas such as HgCdTe material, detector, miniature dewar and cooler to meet the requirements of civil and military operations. This paper describes these activities and present status of HgCdTe technology at Kunming Institute of Physics, and some of the problems we faced and how they were solved.

Optically coupled quantum well infrared detectors

Wen-Gang Wu, Liqiu Cui, De Sheng Jiang, et al.

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This paper proposes and demonstrates for the first time a novel optically-coupled quantum well infrared detector for conversion of mid or far infrared radiation into near infrared radiation. It is in fact the monolithic integration of a GaAs/A1GaAs multiple quantum well intraband photodetector (QWIP) and an InGaAs/GaAs quantum well resonant cavity light emitting diode (RCLED) in which the active region is sandwiched in between a GaAs/AlAs quarter wave n-type distributed Bragg reflector (DBR) and a GaAs/AlGal\As/A1As/AlXGal\As quarter wave p-type DBR. Experimental results show that this new optoelectronic device exhibits an impressive external efficiency because of Fabry-Perot resonance microcavity enhancement and mode-coupling effects in the RCLED, and that its internal efficiency of the photon energy conversion is about unity for high quality InGaAs/GaAs quantum wells. Since near infrared detectors normally have much higher detectivity values than those for far infrared detectors, the proposed detector, demonstrated here by a one-dimensional array, should be easy to scale up into large two-dimensional focal plane arrays (FPAs) and suitable for thermal imaging application using optical interconnection directly. This new unique approach combines the recently developed vertical-cavity surface emitting laser (VCSEL) technology with the newly established QWIP technology both based on GaAs and related epitaxially grown alloys, such as A1GaAs and InGaAs. Its advantage over conventional approach, usually applying an InSb or a HgCdTe detectorarray hybrid bonded to a Si chip for multiplexing, is that it uses a mature materials system and avoids hybrid bonding and any thermal mismatch.

Study of GaAs/GaAlAs infrared photodectors with novel characteristics

Chun-Xia Du, Jun Deng, Qun Li, et al.

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A new type of GaAs/GaAlAs infrared photodetectors based on a new physics mechanism has been designed. Its simulation, manufacture, experiment measurements and analyses have been performed. Some novel important characteristics are obtained which are compared with the conventional GaAs/GaAlAs quantum well infrared photodetectors, such as, its low dark current, large absorption bandwidth, high response speed, low noise, and the choice of suitable operation bias. From our elementary work, the novel features of this kind of device will be very attractive in the application.

Interface properties of HgCdTe passivated with the combination of CdS and ZnS

Gehong Zeng, Jingshao Zhang, Tianzhu Shen

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The process for forming CdS and ZnS films on n and p type of HgCdTe with x - 0.218 in aqueous sulfide solutions is described. The XPS analysis was carried out and photodiodes passivated with deferent thickness of sulfide were fabricated to assess the validity of the procedure. The results indicate that the native sulfide layers formed in this way show almost the same properties as those grown in nonaqueous solutions.

Improved interconnect circuit for high Tc superconducting microbolometer

Fang Qiao Zhou, Zhihong Mai, Xinjian Yi

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A novel interconnect circuit (interface) for high T_c superconducting microbolometer has been designed. The interconnect circuit is composed of a constant-current bias and a silicon preamplifier chip. All of the components are mounted in a liquid nitrogen-cooled Dewar. Our preliminary results demonstrate a proof of principle for designing superconductor-semiconductor hybrid integrate infrared detectors with some electronic process functions.

Real-time measurement of temperature field by colorimetric method

Hua Zhang, Baojian Liao, Jiluan Pan

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Real-time measurement of temperature field is an important but very difficult problem in metallurgy, welding and various hot working process. The authors proposed a colorimetric method for measuring temperature field with ICCD as sensor. Two filters with different wavelength are mounted on a high speed rotating disk in front of the ICCD, so that two images can be taken by ICCD quickly and successively for the colorimetric estimation. Temperature range which can be detected by the designed device is 1100 approximately 1600 K. The measuring time for one field is less than 120 ms. Due to the inherent law of the method, the distance between the object and device has no effect on the measured results, therefore it does not need calibration for measurement at different position, which is one of the great advantages of the proposed method.

Experimental investigation on thermal imaging by a high Tc super conducting microbolometer

Fang Qiao Zhou, Jing Ju, Zhihong Mai, et al.

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In order to examine the performance of high T_c superconducting microbolometer operating as infrared detector, a preliminary thermal imager with linear array infrared detector consisting of 8-element high T_c superconducting microbolometers has been established. The experimental thermal imager consists of the linear array infrared detector, optical system, optic-mechanic scanning system, electronic circuits, and microcomputer. In this paper, the constructures and the operation principles of each parts for this experimental thermal imager are described. The noise mechanism of the imager is also discussed.

Double-band infrared image processing system using rosette scanning

Haifeng Wan, Zhi Liang, Qingchuan Zhang , et al.

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In this paper, a double band infrared image processing system using rosette scanning is introduced. The system is composed of a double band infrared scanning head, a double color detector which works at the ranges of 3 approximately 5 micrometers and 8 - 12 micrometers , a hardware system in order to acquire, process and display the infrared images rapidly. With this system, some infrared targets with different temperature were detected and the corresponding algorithm to recognize targets was studied. The experiments show that the system has good locating accuracy and high recognition probability.

Influence of growth conditions on the qualities of CdxHg1-xTe (0 x 1) layers grown by MOVPE

Chaowang Liu, Bingwen Song, Yue Wang, et al.

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We report the influence of growth conditions on the qualities of CdTe, HgTe and HgCdTe layers grown by MOVPE, CdTe and HgTe layers were grown onto 2 degree(s)(100)GaAs substrates. HgCdTe layers were grown onto hybrid substrates 2 degree(s)(100)CdTe/GaAs with 3 micrometers buffers using interdiffused multilayer process. Surface morphology and compositional uniformity of HgCdTe layers have been investigated. Although the growth conditions have not been optimized, the layers have smooth and specular surface with remarkable featureless except some occasions with elongated hexagonal features. The morphology is sensitive to slight variations of concentrations of reactants, and (100)CdTe/(100)GaAs layers can be grown in a narrow range at Cd-rich conditions. Compositional uniformity of (Delta) x equals +/- 0.005 mol.CdTe over 1 cm² area of HgCdTe layers have been reached for both LWIR and MWIR material. The grown layers can be p- or n-type, depending upon the buffer thickness, Hg concentrations during growth and postgrowth treatment and the substrate temperatures.

Numerical simulation and analysis of the new 8- to 14-um GaAs/GaAlAs quantum well infrared photodetectors

Qun Li, Chun-Xia Du, Jun Deng, et al.

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The simulation of a new type of GaAs/GaAlAs quantum well infrared photodetectors based on a new physics mechanism has been performed. The essential work is concentrated on the device parameters' influence on the energy levels and absorption peaks, they would have important effects on device design. Moreover, a new characteristics-infrared detector with bias-tuned wavelength is proposed.

Research on P+-GexSi1-x/p-Si heterojunction internal photoemission long-wavelength infrared detector

Ruizhong Wang, Peiyi Chen, Peihsin Tsien, et al.

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In this paper, we present a new electrode structure for P⁺-Ge_xSi_1-x/p-Si heterojunction internal photoemission (HIP) long-wavelength infrared detector (LWIRD). The advantages of this structure has been verified by experimental results. The electrical and photoresponse characteristics of the detector with 100 nm-thick Ge_0.3Si_0.7 layer at 77 K are reported. In addition, a new analytic quantum efficiency model for P⁺-Ge_xSi_1-x/p-Si HIP LWIRD is built based on modification of old model. Comparing with old models, it is characterized in that the impact of carriers transporting on quantum efficiency is considered. It is shown that this model is more consistent with actuality than old model through the comparison between the theoretical results and experimental results. The optimal thickness of Ge_xSi_1-x layer can be estimated by this model and the result also agrees with the experiment.

High Tc superconducting microbolometer detector arrays

Zhihong Mai, Xinjian Yi, Xing-Rong Zhao, et al.

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8-element microbolometer detector arrays of high T_c superconducting films have been fabricated using both granular and epitaxial YBCO films deposited by electron beam evaporation with post annealing and laser ablation respectively. The devices were patterned by ion beam milling. The characteristics for optical response of the arrays were investigated in the region of 8 approximately 14 micrometers . A blackbody at the temperature of 500 K was used as a radiation source for sensitivity measurement. The microbolometer array was mounted in a temperature variable dewar. The operating temperature of the array was regulated at the center of the resistive transition edge using a temperature controller. The average noise equivalent power and the average normalized detectivity of the arrays were in the order of 10^-12 WHz^-1/2 and 10⁹ cmHz^1/2W^-1 respectively at the chopping frequency of 10 Hz. The frequency response of the arrays were also studied in our experiments.

Thermal analysis of thin film resistor arrays for dynamic IR scene simulation

Bin Liu, Liping Wang, Baomin Zhang

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The electrically heated thin film resistor array presents promising future to provide dynamic IR scenes for hardware- in-the-loop simulation. Its radiant output is principally affected by the time-dependent temperature distribution on the emitting surface. And the performance is limited principally by the thermal constraints. In this paper, the numerical analysis of heat transfer in the thin film resistor array is conducted by the use of finite difference technique. The investigation is concentrated on thermal crosstalk between neighboring elements and relation of temperature distribution with applied power.

Reflectivities and electronic band structure of Hg0.8Cd0.2Te

Runqing Jiang, Xierong Hu, Jiaxiong Fang, et al.

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The fundamental reflectivity spectrum of Hg_0.8Cd_0.2Te have been investigated. The feature of the spectra is the presence of E₁ and E₂ peaks with the fundamental absorption region. The lower energy peak can be split into a doublet (E₁ and E₁ + (Delta) ₁). A 3D saddle point is used to fit the E₁ and E₁ + (Delta) ₁ critical point and some simulated calculation is done for E₂ at X point. The calculated results are compared with the measured results and prominent features of the dielectric spectra are identified with critical-point transition at the (Lambda) and X points in the Brillouin zone.

Pseudorandom encoding of fully complex modulation to biamplitude phase modulators

Robert W. Cohn, Wenyao Liu

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Pseudorandom encoding is a statstica11ybased, pixel-by-pixel mapping of complex valued modulations Auto modul6tors that do not produce a!! comp1e values.' The resulting far-field 1iffraction pattern closely approximates that from the desired, but unimplementabic, complex modulation. Since the methed is point-oriented, the desired complex modulation can be synthesized and encoded without resorting to time consuming constrained global optimizations e.g. simulated anneding,4 genetic,3 and Gerchberg Saxton4 algorithms. In addition to reducing design time, the resulting diffraction patterns can have reasonably high diffraction efficiencies and low levels of background noise.

Gain performance research and analysis of aluminized MCP in third-generation image tube

Jinliang Yan

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MCP's ion barrier film plays an important role in improving the life of the third-generation image intensifier. This paper analyses the ion barrier film's mechanism, material and structure, and designs a new equipment having the function of quenching cold and ion sputter which is used successfully to deposit an uniform, compact and hard adhesive film at the input of the MCP. Finally, some performance such as electron gain and dark current etc. of the MCP with 40 angstroms thick barrier film are measured and analyzed.

Study of thermo-optical tunable reflecting filter based on dual interference effect

Bing Zheng, Zheng Chen

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A novel tunable optical filter has been proposed and investigated here, which is a thin film-slab substrate combination system, operating on principle of Dual Interference Effect introduced first time. According to theoretical analysis, the reflectance for a specific wavelength varies periodically with the changing of refractive index of the slab substrate for a given thickness of film. Experimentally, the tested samples are fabricated by depositing approximately 90 nm SnO₂ semiconductor film on 3 mm Na-glass substrate, the measured ratio of reflectances at operating wavelength 632.8 nm/670 nm is as high as 15 dB.

Theory of optical transfer function for photodetector arrays

Dazun Zhao, Yong Zhang, Hua-Kuang Liu

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Existence conditions of optical transfer function for discrete imaging systems with focal plane photodetector arrays and aliasing phenomenon due to insufficient sampling intervals are analyzed. A concept of average discrete point spread function based on the characteristics of photodetectors is proposed. A theory of statistical transfer function for discrete imaging systems is suggested.

Photoelectric properties of a voltage-tunable two-color quantum well infrared photodetector

Liqiu Cui, De Sheng Jiang, Yaohui Zhang, et al.

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A new voltage-tunable two-order GaAs/AlGaAs multistacks quantum well infrared photodetector (QWIP) has been investigated in this work. The infrared photodetector consists of GaAs/AlAs/AlGaAs double barrier quantum wells (DBQWs) and GaAs/AlGaAs square quantum wells (SQWs) with photovoltaic and photoconductive dual-mode operation in the 3 approximately 5.3 micrometers and 7.5 approximately 12 atmosphere windows. Experimental and theoretical studies have been conducted on the device physics of the intersubband transitions based on photoexcitation from ground state to different upper subbands including quasibound subband in DBQWs to virtual energy levels within the continuum in SQWs. These allow a better understanding of the optical and transport behaviors of the QWIP. The unique performance and very simple voltage-tunable switching behavior of the two-color GaAs/AlGaAs QWIP are expected to be quite competitive with HgCdTe and InSb infrared photodetectors for large area staring array imaging and two- color or multi-color detecting applications where material uniformity and simple device technology are important.

CCD camera application in the investigaton of optical materials damage processing

Fei Chen, Shao-Xian Meng

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A new detecting system that is used to investigate the damage of optical materials is presented in this paper, which consists of a digital camera and a Nomarski polarized light interferometer. Because of the digitalization and automatization we can investigate the damage processes of optical materials in a much more precision than ever we could. The experimental results agree well with our analysis.

Measurement of peak power of laser pulses using avalanche photodiodes

Qianqian Wang, Jinghai Liu, Rongfu Xu, et al.

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The applications of avalanche photodiodes (APDs) to linear measurement are discussed in this paper. Some factors that affect APDs' responsivity are analyzed in detail. Two available methods to maintain APDs' responsivity constant are proposed and a system which measures the peak power of low-level 1.06 micrometers laser pulses using APD detector is successfully demonstrated.

High-speed imaging by use of a photoswitch array

Anshi Chen, Jing Zu

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A new technique for recording the shadow image of a moving projectile is presented. The technique is both simple to understand as well as efficient in image recording and processing. The key to the method is the way in which the photoswitch array produces two analog output corresponding to the positions of the upper edge and the lower edge of the projectile. The two outputs are converted into a digital data stream and acquired by a computer. A simple computation is applied to reconstruct the image. Analytical results for system transfer function and time response is evaluated and verified experimentally.

New type of multijunction thermopile IR detector

Tietun Sun, Li Hui Guo

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A newly designed thin-film thermopile infrared detector, which as an absorption layer and a sensitive area on two sides are fabricated using integrated-circuit technology. The device uses a series-connected thermocouples array whose `hot' junction are supported on a thin Myler film of 1 - 3 micrometers thickness. By a special method of fasting the shadow mask, the thermopile with 48 Bi-Sb couples for 2 X 2 mm² area produces a responsivity of 50 - 70 V/W and relaxation time of about 70 ms.

High-sensitivity photoelectric pressure sensor based on a monolithic dual photodiode

Weimin Zheng, Tianning Cao, Junxia Qian

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This paper presents a novel and simple photoelectric pressure sensor. The pressure sensing element is a linear capsule with a miniature opaque windowshade on its center. The photo detector is a monolithic dual photodiode. The two photodiodes of this detector are used as reference photodiode and the detection photodiode, respectively. Through this differential structure, the displacement of the windowshade caused by the fluid pressure is picked up, while the influence of the environmental perturbation can be eliminated. The nonlinearity error can be corrected by a single chip computer. This sensor has excellent stability, linearity and high sensitivity as well as good manufacturability. Experiment results show that the minimum detectable pressure is less than 20 Pa with the measurement range of 0 approximately 6 HZ, the nonlinearity error without correction is less than +/- 0.3% within the range of 6000 Pa.

High-integration CMOS vision chips

Guoyu Wang

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CMOS technology, as a popular VLSI technology, is very attractive for achieving `smart' vision devices. This paper introduces two high integration CMOS vision chips, fabricated using unmodified commodity 0.8 micrometers CMOS process, with the resolution of 369 X 287 and 768 X 574. In addition to a photodiode array, two devices include all necessary circuits to drive and sense the array, as well as TV signal formatting and other control functions. On-chip automatic exposure control enables the use of a fixed- aperture lens. On-chip automatic gain control improves dark pictures and on-chip black-calibration maintains image stability. The miniature cameras using the chips enjoy great reductions in size, cost, and power consumption.

Improving the measuring resolution of CCD by curve fitting

Li Ding, Songcan Lai, Xinyi Wu

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When the dimension of measurand is measured with a charge couple device (CCD), the measuring accuracy is limited in interval of array photosensor. It we want to improve the measuring resolution, we often finish it by improving the magnifying power of optical system. But if we do this, we shall limit the measuring range of CCD. If using a analog- digital converter, we can get the pulse amplitude of CCD array photosensor. Using numerical method to the pulse amplitude, we can change intersect value to continuous value. With the segmentation level, we can get a improving resolution. In this paper, we give a hardware frame chart and the calculation course.

Method of using pulse laser to calibrate transient surface temperature detectors

Lieguo Liang, Hanchang Zhou, Deheng Pan

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A dynamic calibration system for transient surface temperature detectors is introduced. In this system a pulse laser and a continuous laser are used as excitation sources. The static and dynamic calibrations have been carried out respectively with the use of the continuous CO₂ laser and Nd-glass pulse laser. Several quick response thermocouples have been tested on the system. The experimental results have shown that this calibration system can be used to calibrate transient surface temperature detectors with a time response on order of microseconds.

Applications of a new time-frequency analysis in high-G accelerometer dynamic calibration by laser differential Doppler technique

Zhijie Zhang, Jing Zu

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Based on high-G accelerometer dynamic calibration by laser differential Doppler technique, the time-frequency analysis of the Doppler signal is presented. The analysis aims at obtaining its amplitude linearity after an accelerometer is single-calibrated. The system is presented. And the time- frequency analysis and its algorithm flow diagram are described in detail. The calculating results are given.

Measurement of noise of photovoltaic HgCdTe and InSb infrared detector

Zhongyun Tian, Ruoxi Ji, Shengqiong Lei, et al.

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An investigation of noises in two linear detector has been described in this paper. Noises were measured at 80 K from 10 - 100 KHz at different reverse bias. In all samples of HgCdTe and InSb. 1/f noises were observed. In order to decrease 1/f noise, processing needs improving further. The various noises have been discussed.

Influence of reverse bias voltage and light intensity on some properties of position-sensitive detector (PSD)

Ai-ming Lu, Hong-xing Yuan, Anzhi He, et al.

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The influence of reverse bias voltage and light intensity on the linearity, position precision and response time of position sensitive detector (PSD) is described from the view of engineering application in this paper. And a series of verifying experiments are carried, the results proved that the reverse bias voltage and the working intensity of laser have little influence of linearity of PSD, but their influence on the bias of the output signal of PSD can't be neglected. At the end of this paper some conclusions are summarized.

Characterization of HgCdTe epilayers grown on GaAs(211)B by molecular beam epitaxy

Shida Chen, Xianzhong He, Li Lin

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The growth of HgCdTe(MCT) epilayers on GaAs(211)B substrate by molecular beam epitaxy (MBE) have been reported. The growth procedure of MCT is described. Various characterization techniques have been employed for evaluating the quality of MCT epilayers. A planar PV array are fabricated for assessment of MCT epilayer quality. The present results represent an important step toward the demonstration of MBE epilayers for fabrication of focal plane arrays.

Four-unit composite thin film IR detector

Zhen Pang, Ben-He Jiang, Huanjun Qi, et al.

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The composite thin-film IR image detector consists of pyroelectric, LCD and electronic information processing technique. It can reproduce thermal image directly under the condition of uncooled, room temperature. The pyroelectric film signal charge amplifier and LCDs are its mainly components. It is respectively composed of PVDF (or PVDF- TGS, PVDF-PZT) film, TFT and LC film. The device properties parameter are relatively high level, D^* approximately 10⁸cmHz^1/2w^-1, NEP approximately 10^-9 W and NETD approximately 10^-1 K. The four units is a IR signal detector and to make a foundation for 32 X 32 units and above of multiunits plane array. It is a novel, convenient thermal detecting device and possesses a quite prospects of development and application.

Performance prediction and computer simulation of staring thermal imaging systems with OTL96

Hongbing Fang, Jian Jiao, Defu Pi, et al.

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According to the characteristics of staring thermal imaging systems, a software named OTL96 was completed. The performance curves of the staring thermal imaging systems can be predicted from this software. In OTL96, an improvement method has been developed for calculating the minimum resolvable temperature difference. The critical coefficient is introduced in this method and the prediction result is more consistent with the experiment. OTL96 also has the function of imaging simulation, which can simulate the formation process of the thermal image. This paper illustrates some techniques used in OTL96 and some results will be introduced at the same time.

Detectivity limit of the LWIR photoconductive HgCdTe detector

Wei-Jian Zheng

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The photoconductive (PC) detectivity of longwave infrared (LWIR) HgCdTe detector at low and very low temperature is calculated, and it can be concluded that detectivity limit is related to parameters of material, it is restricted by both specifications of material as well as device and application requirement of IR system. Natural limit and technical limit of PC detectivity of LWIR HgCdTe at liquid nitrogen temperature zone is presented.

Bridgman growth and assessment of CdTe and Cd1-yZnyTe crystals

Yu Long Mo, Quanling Yue, Chaowang Liu, et al.

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In order to meet with the epitaxial growth of large area Hg_1-xCd_xTe (MCT) with various compositions for infrared focal plane arrays, CdTe and Cd_1-yZn_yTe (y equals 0.020, 0.025 and 0.040 for various x) crystals with 120 mm length and 20 - 40 mm diameter have been successfully synthesized and grown by the vertical Bridgman method. These crystals were grown unseededly or seededly and free of any macroscopic defects e.g. micro-cave and crackles. Wafers with areas from 12 X 18 mm² to 30 X 35 mm² in the <111> orientation have been obtained from large grain of the ingot. Effects of changing the ampoule base shape upon the crystal growth have also been investigated. A necked ampoule bottom is preferred to ones employing seeding. Assessments of the samples have included infrared transmission (range 2.4 - 24 micrometers ), etch pit density, X-ray photography and three-crystal rocking curve measurement. Good quality MCT epitaxial films (areas of 12 X 18 mm² and 20 X 20 mm²), as demonstrated by good surface topography, electrical parameters, have been grown by liquid phase epitaxy and metal organic chemical vapor epitaxy onto CdTe(CT) and Cd_1-yZn_yTe(CZT) substrate materials produced in our study.

8x8 silicon photodiode matrix module

Dawei He, Jinggui Lu, Fuwen Zhang

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8 X 8 silicon photo diode matrix module has been successfully fabricated by hybrid integrating technique. In this paper, the principle, the design, the structure, fabrication process and its main parameters of PIN-PD matrix module which has special arrangement of electrode and structure of piling up optical-electro isolation are mainly described.

Experiment and research on the TDI CCD camera

Haining Wang, Zhonghui Wei

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At present, CCD is widely applied in many fields. Here, we introduce you a special linear area CCD camera which uses Time-Delay-Integration (TDI) technique to provide high sensitivity, high speed, high spatial resolution and wide dynamic range performance under low light conditions. TDI is a method of scanning which provides greater sensitivity than other video scanning methods, and the interface that it needs is quite different from conventional ones. In the paper, the principle and the features are presented. In order to apply the TDI method and verify the effect, we do an experiment of grabbing moving image through using CT-E1 and CL-E2 2048X96 TDI Line Scan CCD camera produced by DALSA INC.. We design a grabber and make a complete system by ourselves. The system includes: camera, camera control, frame grabber, revolving stage, PC. The result indicates that when the line-shift-rate of the CCD camera is not synchronized with the rate of moving object, the image that we obtain is not clear. But when we use phase-shift- compensation technique and make the line-shift-rate of the camera match the rate of the image, we can get very distinct image.

Imaging approach of pyroelectric FPAs using LCDs

Huanjun Qi, Ben-He Jiang, Zhen Pang

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This paper approaches a novel pyroelectric imaging device. We combined the IR pyroelectric FPAs elements with LCDs elements, and studied the possibility of this test. The study of pyroelectric FPAs is a new, important section of IR FPAs, and the pyroelectric FPAs has important and widely usage, but the display section of the equipment using FPAs is more complicated. Researchers have studied the pyroelectric FPAs deeply, and have made some theory and test progress. With the development of film-making and the high- integrated degree of the amplified circuit, the signal that received by the detector can be amplified to drive the LCDs directly. We used the plane-display property of the LCDs, and made the LCDs as the display element of the pyroelectric FPAs detectors, and mounted the LCDs on the back of the pyroelectric FPAs. The output signal of the amplifier is as an additional electric field of an external one, and the LCDs is modulated by the additional electric field and it can display the heat field of the object than detected by the pyroelectric IR FPAs detectors.

Coupling efficiency of metal gratings in a normal incident GaAs/AlGaAs quantum well infrared detector

Yu Jun Yang, Guanqun Xia, Shichang Zou, et al.

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A numerical calculation of coupling efficiency of planar metal grating coupled GaAs/AlGaAs quantum well infrared detectors has been made in this work. The results showed that the coupling efficiency is a function of the ratio of the grating period (Lambda) to the intersubband resonance wavelength (lambda) for various degrees of metal filling. In the vicinity of n(Lambda) /(lambda) < 1 (n is the refractive index), filling factors round 0.5 - 0.7 give large longitudinal electric-field components, which induces a strong coupling to the intersubband absorption in the quantum well structures of the semiconductor. Numerical calculations provide detailed guidelines for obtaining optimum coupling for GaAs/AlGaAs quantum well infrared detectors.

Surface pretreatment of LPE HgCdTe epilayer for passivation technology of photodiode array

Yi Li, Song He

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A new surface pretreating method of the LPE HgCdTe surface involves three steps. The state of the surface before and after the pre-treatment process has been investigated by Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy. The treated surface following the processes is compared to the untreated surface. The results show the Electron Channel Pattern and morphology of the treated surface are better than that of the untreated surface. The optical and electrical parameters of before and after the treated epilayers have not changed. The oxides and contaminants have been reduced and eliminated. The photodiode arrays with good performance have been fabricated on the LPE HgCdTe which is treated as the described approach. The experimental results indicate that the appropriate surface pre-treatment is an important part of the photodiode array technology.

Ultraweak bioluminescence imaging and image processing

Tianming Chen, Susheng Wang, Qin Li, et al.

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A photon counting imaging system which can detect emission down to the order of 1 counts cm^-2 sec^-1 (at the photocathode) has been developed, and it has been used to obtain the ultraweak bioluminescence images of a living Kunming mouse. In this paper, we give statistical analysis for calculation of the photon distribution in images obtained, and we use Chi-square ((chi) ²) statistic to get signal and noise distribution to process these images. It has been proved that the imaging system has the ability in detecting ultraweak bioluminescence of animals, and the statistical method for image processing can effectively increase the signal/noise ratio and improve the image quality.

Digital CMOS active pixel image sensor for multimedia applications

Zhimin Zhou, Bedabrata Pain, Jason C.S. Woo, et al.

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Two charge-scaling successive approximation A/D converters for on-focal-plane column-parallel data processing in CMOS active pixel image sensors (APS) are presented. The converters are designed in a thin but long fashion to fit a pitch size of 40 micrometers for 2.0 micrometers technology and 24 micrometers for 1.2 micrometers technology. Designed for multimedia and other commercial and industrial applications, each in column A/D converter achieves a 8 bit resolution and accuracy with a signal swing of 1 V. Maximum conversion rate exceeding 200 kHz enables high speed digital readout beyond 200 frames/sec for large format 1 K X 1 K CMOS image sensors. A prototype device of 64 X 64 APS image array with 8 bit digital output was demonstrated up to 1 kHz frame rate, and with column-wise non-uniformity less than 2 LSBs.

Detectors, Focal Plane Arrays, and Applications

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