Landau-level lifetimes in PbTe nipi superlattices, PbTe/PbEuTe and InAs/AlSb quantum wells

Landau-level lifetimes are determined from saturation cyclotron resonance (CR) in wide parabolic wells, quantum wells and bulk PbTe–Pb_1−xEu_xTe systems. These narrow gap structures exhibit strong band non-parabolicity necessary to terminate the normally equi-spaced Landau-level ladder. It was not possible to saturate the bulk sample, but short lifetimes, of between 1.5 and 8 ps, were obtained for the wide parabolic well and the quantum well, respectively, utilising a multi-level rate equation model. We also report the first pump–probe cyclotron resonance result in an InAs–AlSb quantum structure. The pump–probe experiment provides a direct determination of the lifetime, giving τ=40 ps in this InAs–AlSb sample. This shows good agreement with an 8×8k·p calculation.     

Three-dimensional imaging with detector arrays on arbitrarily shaped surfaces

Conventional multiview imaging systems commonly utilize a planar lenslet array and a rigid, flat image sensor in the pickup stage to capture different views of the scene. In this Letter, we remove this constraint by proposing the concept of three-dimensional (3D) imaging with detector arrays that may conform to arbitrarily shaped surfaces or platforms. A nonplanar detector array configuration can be used in combination with a flexible lenslet array to capture different views. The orientation and optical axes of individual image sensing elements could vary. A point-by-point 3D reconstruction algorithm is described and the feasibility of the proposed approach is demonstrated through simulated imagery.     

Cold radiation shields for IR detector arrays

Off-set and integral cold shields are compared for cold shield shading effects when used with frontside and backside irradiated IR arrays. The integral cold shield, within its range of application, eliminates cold shield shading for frontside arrays and is more desirable. For backside arrays, off-set cold shield shading can be significantly reduced to tolerable levels when the array is prepared on thick transparent substrates. For these arrays, the integral cold shield is more difficult to implement and thus less desirable than the off-set cold shield.     

Demonstration of large format mid-wavelength infrared focal plane arrays based on superlattice and BIRD detector structures

We have demonstrated the use of bulk antimonide based materials and type-II antimonide based superlattices in the development of large area mid-wavelength infrared (MWIR) focal plane arrays (FPAs). Barrier infrared photodetectors (BIRDs) and superlattice-based infrared photodetectors are expected to outperform traditional III–V MWIR and LWIR imaging technologies and are expected to offer significant advantages over II–VI material based FPAs. We have used molecular beam epitaxy (MBE) technology to grow InAs/GaSb superlattice pin photodiodes and bulk InAsSb structures on GaSb substrates. The coupled quantum well superlattice device offers additional control in wavelength tuning via quantum well sizes and interface composition, while the BIRD structure allows for device fabrication without additional passivation. As a demonstration of the large area imaging capabilities of this technology, we have fabricated mid-wavelength 1024 × 1024 pixels superlattice imaging FPAs and 640 × 512 MWIR arrays based on the BIRD concept. These initial FPA have produced excellent infrared imagery.     

InAs/GaSb superlattices for advanced infrared focal plane arrays

We report on the development of high performance focal plane arrays for the mid-wavelength infrared spectral range from 3–5 μm (MWIR) on the basis of InAs/GaSb superlattice photodiodes. An investigation on the minority electron diffusion length with a set of six sample ranging from 190 to 1000 superlattice periods confirms that InAs/GaSb superlattice focal plane arrays achieve very high external quantum efficiency. This enabled the fabrication of a range of monospectral MWIR imagers with high spatial and excellent thermal resolution at short integration times. Furthermore, novel dual-color imagers have been developed, which offer advanced functionality due to a simultaneous, pixel-registered detection of two separate spectral channels in the MWIR.     

Beam position estimation by means of detector arrays

The application of detector arrays for the estimation of optical beam position is considered. An estimation algorithm is synthesised, and estimator performance is analysed. Estimator performance depends on the number of detectors in the array and on the received radiation and its associated shot noise. It is shown that by choosing an appropriate number of detectors in the array, the designer can always drive the estimator into shot-noise-limited operation. In this case, the performance may be either quantum-limited or background-noise limited, depending on the energy of the optical beam and on the background field.     

Target azimuth estimation by means of optical detector arrays

Estimation of a target azimuth by means of arrays of optical detectors is investigated. A maximum likelihood algorithm of estimation is developed, and simpler suboptimum algorithms are described. The performance of the maximum likelihood estimator is analysed. It is shown that for a small detector beamwidth the array accuracy becomes an oscillating function of the target azimuth. The minimum accuracyà depends on the detector beamwidth and onN, the number of detectors in the array. The largerN, the largerÃ; with a givenN, the optimum beamwidth which provides maximum accuracy can be found. The optimum beamwidth implies 100% overlapping of the detector beams, i.e., the semiangle of detector sensitivity should equal the angular separation of the detectors.     

Pulsed laser deposited superlattices based on perovskite oxides

Recent advances made in the field of pulsed laser deposited superlattices made up of perovskite oxides are reviewed. The superconducting properties and the effect of adjacent layers in ultra-thin YBCO are studied in YBCO/(Pr_xY_1−x)BCO superlattices. We describe the effects of layering in (La_0.7Ba_0.3)MnO₃for the purposes of fundamental studies and possible applications of these newly recognized colossal magnetoresistance materials.     

基于荧光技术的啶虫咪农药检测仪的研究

设计了一套基于线阵CCD光电转换原理的荧光检测系统。利用该系统实现了对啶虫咪农药荧光光谱特性的检测。用CCD检测仪取代了常用的光电转换器件——光电倍增管，通过与光栅结合实现了光谱的快速分析。根据噪声和信号在小波变换下表现出的截然不同的性质，提出基于小波变换技术的荧光信号特征提取及消噪方法。结果表明，采用小波去噪能更好地保留荧光光谱峰值处的信息，可以大大提高系统的检测精度。     

Infrared detector arrays with multiplexing cryogenic read-out electronics for isophot

Cryogenic Read out Electronic circuits (CRE) are developed in a CMOS technology for the multiplexing operation at temperatures around 4 K and below of extrinsic photoconducting detectors and detector arrays of Ge and Si in the Infrared Space Observatory (ISO) instrument ISOPHOT covering a wavelength region between 10–200 μm. Measurements on the 66 elements spectroscopic array ISOPHOTS2 show performance data of an NEP around 4 × 10⁻¹⁷W/√Hz and a voltage responsivity of 10¹⁴V/Ws at low background operation.     

Lenticular arrays based on liquid crystals

Lenticular array products have experienced a growing interest in the last decade due to the very wide range of applications they can cover. Indeed, this kind of lenses can create different effects on a viewing image such as 3D, flips, zoom, etc. In this sense, lenticular based on liquid crystals (LC) technology is being developed with the aim of tuning the lens profiles simply by controlling the birefringence electrically. In this work, a LC lenticular lens array has been proposed to mimic a GRIN lenticular lens array but adding the capability of tuning their lens profiles. Comb control electrodes have been designed as pattern masks for the ITO on the upper substrate. Suitable high resistivity layers have been chosen to be deposited on the control electrode generating an electric field gradient between teeth of the same electrode. Test measurements have allowed us to demonstrate that values of phase retardations and focal lengths, for an optimal driving waveform, are fairly in agreement. In addition, results of focusing power of tuneable lenses were compared to those of conventional lenses. The behaviour of both kinds of lenses has revealed to be mutually similar for focusing collimated light and for refracting images.     

Nonlinear Bragg structures based on ZnS/ZnSe superlattices

Nonlinear optical response of periodic ZnSe/ZnS heterostructures is reported using interband excitation of a ZnSe sublattice by nano-, pico- and femtosecond laser pulses. A considerable shift of the reflection spectrum and large relative reflection changes were observed in a wide spectral range corresponding to the transparency region of ZnSe far from the intrinsic absorption onset. Evaluated refraction-index change is about −0.05 with the relaxation time being about 3 ps. In the case of femtosecond excitation, a wide-band nonlinear response is observed for both one-photon near-UV and two-photon near-IR excitation. The nonlinear refraction is supposed to be controlled by population-induced absorption changes in ZnSe single crystals and relevant refraction-index modification via Kramers–Kronig relations. The nonlinearity relaxation time is supposed to trace a transition from a non-equilibrium to a quasi-equilibrium distribution of electrons and holes within ZnSe conduction and valence bands, respectively, rather than the electron–hole recombination time. The nonlinearity mechanism does not reduce to just population-dependent absorption saturation, but essentially results from the specific distribution function in the first instance after excitation.     

Stressed and unstressed Ge:Ga detector arrays for airborne astronomy

We have constructed and used two dimensional arrays of both unstressed and stressed Ge:Ga photoconductive detectors for far-infrared astronomy from the Kuiper Airborne Observatory (KAO). The 25 element (5×5) arrays are designed for a new cryogenically cooled spectrometer, the MPE/UCB Far-Infrared Imaging Fabry-Perot Interferometer (FIFI). All of the pixels for the stressed array performed well on the first flights with FIFI; 25% of the detectors in the array are more sensitive than our best single element detector, with background limited noise equivalent powers (NEPs)3.0×10^–15 W Hz^–1/2 at 158 m and 40 km s^–1 spectral resolution. The average array element performs within±15% of this value. With a bias field of 0.1 V/cm, the average detector response is 20±6 Amp/Watt at 158 m. The cutoff wavelength and response also compare well with our single element detectors. The unstressed array delivers significantly better performance than our single element detector due to the lower thermal background in the new spectrometer. The average background limited NEp at 88 m and 35 km s^–1 spectral resolution is 7×10^–15 W Hz^–1/2. The least sensitive pixel is only 40% less sensitive. The unstressed array response at 88 m with a bias field of 1 V/cm is 5±1 Amp/Watt. Twenty four of the 25 elements worked on the first flights-on subsequent flights all channels have worked. Some of the exciting new science possible with far-infrared detector arrays is also discussed.     

基于“猫眼效应”的狙击手光电探测仪

为从技术层面上提高反狙击能力,通过分析狙击步枪瞄准镜的反射特性,利用线阵CCD捕捉瞄准镜回波信号研制出主动式狙击手光电探测仪。介绍了探测仪的主要指标参数,并模拟实际使用环境验证了其探测效果。试验结果表明:在城市作战中狙击手通常伏击的距离为20 m~200 m,探测仪可准确探测微光瞄准镜及口径为32 mm、40 mm、42 mm和50 mm的白光瞄准镜,且不受镜子和手电筒凹面镜等反射体干扰,但对加装蜂窝板的瞄准镜,当距离大于80 m后无法可靠探测。     

基于线阵CCD反狙击探测仪的研制

针对传统反狙击探测方法主动性差、定位精度低的不足,提出了一种运用"猫眼效应"原理实现激光主动探测的反狙击方法.系统采用半导体激光器作为光源,以线阵CCD作为激光回波探测器.光学系统将一定角度的接收视场和线阵CCD的2 160个像元位置相对应,探测精度可达mrad量级.CCD工作时序由FPGA产生,其程序可在线编译.结合帧减和阈值比较算法,最大程度上剔除了噪声,试验探测距离可达250 m.     

Multichannel prototype detector based on segmented straws

The design and technology of assembling a prototype detector based on segmented straws with a granularity of 4 cm² are considered. The prototype with a sensitive area of 400 × 200 mm contains two straw planes with a diameter of 4 mm shifted with respect to each other by the straw radius. The total number of registration channels is 360. The results of a test bench study of the prototype are presented.     

基于四象限探测器的激光导引镜头的研制

为了满足激光制导对大视场、高线性度探测的性能要求,基于激光制导炸弹的应用需求,介绍了四象限探测器的工作原理和特点,分析了光斑大小、能量均匀性、线性度、探测距离等参数对探测精度的影响;结合系统性能指标,选择了合理的光学系统结构类型,完成了光学系统设计和光机结构设计;利用畸变、点列图、足迹图、能量集中度等指标对系统性能进行了评价,并分析了目标大小和探测距离对光斑大小的影响。测试结果表明,激光导引镜头总视场为±20°、线性视场为±10°、目标大小为1.5~2.4 m、探测距离为50 m~4 km、测角精度优于0.2°,能够满足激光导引的需求。     

Ultra-broadband absorber based on cascaded nanodisk arrays

An ultra-broadband perfect absorber consisting of cascaded nanodisk arrays is demonstrated by placing insulator-metal-insulator-metal nanodisks on insulator-metal film stacks. The absorber shows over 90% absorption in a wavelength range between 600 nm and 4000 nm under transverse magnetic (TM) polarization, with an average absorptivity of 91.5% and a relative absorption bandwidth of 147.8%. The analysis of the electric field and magnetic field show that the synergy of localized surface plasmons, propagating surface plasmons, and plasmonic resonant cavity modes leads to the ultra-broadband perfect absorption, which accords well with the results of impedance-matched analysis. The influences of structural parameters and different metal materials on absorption performance are discussed. Furthermore, the absorber is polarization-independent, and the absorption remains more than 90% at a wide incident angle up to 40° under TE polarization and TM polarization. The designed ultra-broadband absorber has promising prospects in photoelectric detection and imaging.     

地面长波红外高光谱成像气体探测研究

报道了地面长波红外遥测的新进展 ,具体阐述了窗扫时空调制傅里叶光谱成像技术的实现过程.演示装置基于角锥反射镜M ichelson干涉具 ,构成了空间调制干涉 ;采用了制冷型长波红外焦平面探测器组件 ,通过对数据立方体的采集、重组、基线校正、切趾、相位校正和傅里叶变换等处理 ,实现了长波红外波段高光谱成像.自研的CHIPED-1长波红外高光谱成像原理实验装置的探测灵敏度指标噪声等效辐射通量密度NESR在单次采样时达到了5.6 × 10-8 W · (cm-1 · sr · cm2 )-1 ,与商品化时间调制干涉高光谱成像仪相当 ;反映了技术的先进性 ,并留有较大的改进空间.通过测试聚丙烯薄膜的透过率曲线 ,CHIPED-1红外高光谱成像原理实验装置的光谱响应范围达到了11. 5 μm.文章还以室外高楼和乙醚气体的探测实验为例 ,研究了二维分布化学气体VOC的高光谱成像探测方法.在复杂背景和低试验浓度情况下 ,从同一波数的红外光谱切片上 ,观察不出乙醚蒸气的存在 ,但是进行了差谱处理后 ,可以清楚看到乙醚蒸气的空间分布.高光谱方法应用在有机蒸气VOC的红外探测领域 ,相对于宽波段热成像方法 ,具有灵敏度高、抗干扰能力强和识别种类多等诸多优势.