Spatially modulated scene illumination for intensity-compensated two-dimensional array photon-counting LiDAR imaging

Photon-counting LiDAR using a two-dimensional(2D)array detector has the advantages of high lateral resolution and fast acquisition speed.The non-uniform intensity profile of the illumination beam and non-uniform quantum efficiency of the detectors in the 2D array deteriorate the imaging quality.Herein,we propose a photon-counting LiDAR system that uses a spatial light modulator to control the spatial intensity to compensate for both the non-uniform intensity profile of the illumination beam,and the variation in the quantum efficiency of the detectors in the 2D array.By using a 635 nm peak wavelength and 4 mW average power semiconductor laser,lab-based experiments at a 4.27 m stand-off distance are performed to verify the effectiveness of the proposed method.Compared with the unmodulated method,the standard deviation of the intensity image of the proposed method is reduced from 0.109 to 0.089 for a whiteboard target,with an average signal photon number of 0.006 per pixel.

An FPGA-Based Pulse Pile-up Rejection Technique for Photon Counting Imaging Detectors

A novel FPGA-based pulse pile-up rejection method for single photon imaging detectors is reported. Tile method is easy to implement in FPGAs for real-time data processing. The rejection principle and entire design are introduced in detail. The photon counting imaging detector comprises a micro-channel plate （MCP） stack, and a wedge and strip anode （WSA）. The resolution mask pattern in front of the MCP can be reconstructed after data processing in the FPGA. For high count rates, the rejection design can effectively reduce the impact of the pulse pile-up on the image. The resolution can reach up to 140μm. The pulse pile-up rejection design can also be applied to high-energy physics and particle detection.

Modeling the photon counting and photoelectron counting characteristics of quanta image sensors

A signal chain model of single-bit and multi-bit quanta image sensors(QISs)is established.Based on the proposed model,the photoresponse characteristics and signal error rates of QISs are investigated,and the effects of bit depth,quantum efficiency,dark current,and read noise on them are analyzed.When the signal error rates towards photons and photoelectrons counting are lower than 0.01,the high accuracy photon and photoelectron counting exposure ranges are determined.Furthermore,an optimization method of integration time to ensure that the QIS works in these high accuracy exposure ranges is presented.The trade-offs between pixel area,the mean value of incident photons,and integration time under different illuminance level are analyzed.For the 3-bit QIS with 0.16 e-/s dark current and 0.21 e-r.m.s.read noise,when the illuminance level and pixel area are 1 lux and 1.21μm^(2),or 10000 lux and 0.21μm^(2),the recommended integration time is 8.8 to 30 ms,or 10 to21.3μs,respectively.The proposed method can guide the design and operation of single-bit and multi-bit QISs.

X-ray photon counting detectors for preclinical and clinical applications

Photon counting detectors(PCDs) have attained w ide use in X-ray imaging for various preclinical and clinical applications in the past decade. This paper briefly review s the preclinical and clinical applications of PCDs based X-ray imaging systems.Starting with an introduction of X-ray single photon detection mechanism,the brief review first describes tw o major advantages of utilizing PCDs: photon energy resolving capability and electronic noise elimination. Compared to energy integrating detectors(EIDs),the aforementioned advantages make PCDs more favorable in X-ray imaging with profound benefits such as enhanced tissue contrast,decreased image noise,increased signal to noise ratio,decreased radiation dose to the small animals and patients,and more accurate material decomposition. The utilizations of PCDs in X-ray projection radiography and computed tomography(CT)including micro-CT,dedicated breast CT,K-edge CT,and clinical CT are then review ed for the imaging applications ranging from phantoms to small animals and humans. In addition,optimization methods aiming to improve the imaging performance using PCDs are briefly review ed. PCDs are not flaw less though,and their limitations are also discussed in this review. Nevertheless,PCDs may continuously contribute to the advancement of X-ray imaging techniques in future preclinical and clinical applications.

Fast fluorescence lifetime imaging techniques:A review on challenge and development

Fluorescence lifetime imaging microscopy(FLIM)is increasingly used in biomedicine,material science,chemistry,and other related research fields,because of its advantages of high specificity and sensitivity in monitoring cellular microenvironments,studying interaction between proteins,metabolic state,screening drugs and analyzing their efficacy,characterizing novel materials,and diagnosing early cancers.Understandably,there is a large interest in obtaining FLIM data within an acquisition time as short as possible.Consequently,there is currently a technology that advances towards faster and faster FLIM recording.However,the maximum speed of a recording technique is only part of the problerm.The acquisition time of a FLIM image is a complex function of many factors.These include the photon rate that can be obtained from the sample,the amount of information a technique extracts from the decay functions,the fficiency at which it determines fluorescence decay parameters from the recorded photons,the demands for the accuracy of these parameters,the number of pixels,and the lateral and axial resolutions that are obtained in biological materials.Starting from a discussion of the parameters which determine the acquisition time,this review will describe existing and emerging FLIM techniques and data analysis algo-rithms,and analyze their performance and recording speed in biological and biomedical applications.

Imaging properties of a tetra wedge readout

The decoding principle of a tetra wedge anode, which is a development of the wedge and strip anode, is described. The influence of charge cloud size on decoding accuracy is studied using the Monte Carlo method. Simulation results show that the decoding error is large when the size of charge clouds collected by the anode is small. Thus, the charge clouds collected by the tetra wedge anode should reach a necessary size to ensure accurate decoding. Finally, using the ultraviolet photon counting imaging system, the linearity and the spatial resolution of the system are tested. Experimental results show that the system has a good linearity and the spatial resolution is better than 100 μm.

Analysis of Wide-Bandgap Material OPFET UV Detectors for High Dynamic Range Imaging and Communication Applications

The ultraviolet (UV) photoresponses of Wurtzite GaN, ZnO, and 6H-SiC-based Optical Field Effect Transistor (OPFET) detectors are estimated with an in-depth analysis of the same considering the generalized model and the front-illuminated model for high resolution imaging and UV communication applications. The gate materials considered for the proposed study are gold (Au) and Indium-Tin-Oxide (ITO) for GaN, Au for SiC, and Au and silver dioxide (AgO2) for ZnO. The results indicate significant improvement in the Linear Dynamic Range (LDR) over the previously investigated GaN OPFET (buried-gate, front-illuminated and generalized) models with Au gate. The generalized model has superior dynamic range than the front-illuminated model. In terms of responsivity, all the models including buried-gate OPFET exhibit high and comparable photoresponses. Buried-gate devices on the whole, exhibit faster response than the surface gate models except in the AgO2-ZnO generalized OPFET model wherein the switching time is the lowest. The generalized model enables faster switching than the front-illuminated model. The switching times in all the cases are of the order of nanoseconds to picoseconds. The SiC generalized OPFET model shows the highest 3-dB bandwidths of 11.88 GHz, 36.2 GHz, and 364 GHz, and modest unity-gain cut-off frequencies of 4.62 GHz, 8.71 GHz, and 5.71 GHz at the optical power densities of 0.575 μW/cm2, 0.575 mW/cm2, and 0.575 W/cm2 respectively. These are in overall, the highest detection-cum-amplifi-cation bandwidths among all the investigated devices. The same device exhibits the highest LDR of 73.3 dB. The device performance is superior to most of the other existing detectors along with comparable LDR, thus, emerging as a high performance photodetector for imaging and communication applications. All the detectors show considerably high detectivities owing to the high responsivity values. The results have been analyzed by the photovoltaic and the photoconductive effects, and the series resistance effects and will aid in conducting further research. The results are in line with the experiments and the commercially available software simulations. The devices will greatly contribute towards single photon counting, high resolution imaging, and UV communication applications.

感应读出延时线阳极光子计数探测器研究

针对空间天文、生物荧光、光谱测量等领域对高灵敏、大面阵探测器的应用需求,研制出基于感应读出方式的延迟线阳极光子计数成像探测器。该探测器由微通道板、延时线阳极以及读出电路组成,其中延时线阳极的性能直接影响探测器的成像质量。作为一种电荷感应读出延时线阳极,该阳极利用信号到达的时间差解码入射光子的位置,可获得高的探测灵敏度和大的成像面积,同时简化了工艺难度并提升了可靠性。设计了感应读出延时线阳极,理论分析了探测器不同设计参数及材料对感应电荷量的影响,提出了解决异层电极间感应电荷量难以平衡的方法。据此研制出了收集面积为40 mm×40 mm的位敏阳极。测试结果表明该阳极信号传输衰减小于10%,极间串扰小于3%。利用该阳极进行了光子计数成像实验,获得了优于150μm的空间分辨率,为研制可应用于天文紫外光谱测量的大面阵、高灵敏探测器提供了理论依据及实验指导。

Three-dimensional imaging lidar system based on high speed pseudorandom modulation and photon counting

High speed pseudorandom modulation and photon counting techniques are applied to a three-dimensional imaging lidar system.The specific structure and working principle of the lidar system is described.The actual detector efficiency of a single-photon detector in an imaging system is discussed,and the result shows that a variety of reasons lead to the decrease in detection efficiency.A series of ranging and imaging experiments are conducted,and a series of high-resolution three-dimensional images and a distance value of 1200 m of noncooperative targets are acquired.

Two-dimensional photon counting imaging detector based on a Vernier position sensitive anode readout

A two-dimensional photon counting imaging detector based on a Vernier position sensitive anode is reported. The decode principle and design of a two-dimensional Vernier anode are introduced in detail. A photon counting imaging system was built based on a Vernier anode. The image of very weak optical radiation can be reconstructed by image processing in a period of integration time. The resolution is superior to 100 μm according to the resolution test. The detector may realize the imaging of very weak particle flow of highenergy photons, electrons and ions, so it can be used for high-energy physics, deep space exploration, spectral measurement and bio-luminescence detection.

Experimental research of the energy bins for K-edge imaging using a photon counting detector:a phantom and mice study

Purpose K-edge imaging based on the photon counting detectors(PCDs)is an effective enhanced imaging method because the PCDs are conducive to the K-edge imaging due to the adjustable energy thresholds.The energy bins significantly affect the image quality of the K-edge imaging,but the conventional energy bins used for K-edge imaging are continuous which weaken the K-edge signal and decline the image quality.Hence,how to get a better K-edge signal by the optimized energy bins is the key point for the K-edge imaging based on the PCDs.Method This paper experimentally studied the influence of the energy bins used for the K-edge imaging based on the PCDs.The conventional energy bins were determined by the theoretical-attenuation method(TAM),and the optimized energy bins were determined by the threshold-scan method(TSM).For the phantom and mice imaging,we performed both the K-edge subtraction algorithm and the K-edge decomposition algorithm on the projections obtained by the energy bins which were determined by the TAM and TSM.The image quality was compared using the CNR of the objective area.Results The experimental results showed that the energy bins identified by the TSM had a better performance than the TAM in both imaging methods.The TSM improved the CNR by~39%than the TAM in the phantom results and could better highlight the areas where the contrast agents are enriched(such as the kidney).Conclusions The optimized energy bins can better highlight the K-edge signal than the conventional energy bins which can improve the image quality and have the potential to reduce the amount of the contrast agents.

光子计数探测器技术应用进展

光子计数探测器(PCD)是一种用于检测X射线光子的装置,能够将光子能量直接转化为电信号,从而实现对光子的计数和测量。基于PCD的能谱CT技术(PCD-CT)可以提供额外的能谱成像信息,改善成像质量,同时降低辐射剂量。相较于能量积分探测器(EID),PCD具有能量转换效率高、成像质量好、结构设计精巧、应用范围广等优势,在超低剂量CT、特定病症检验及工业检测中具有广阔的应用前景。综述PCD-CT在能谱CT成像中的应用,为其在临床医疗诊断与工业应用提供有益参考。

Single-Photon Lidar for Fast Imaging at Low SBR and Few Photons

In low-light conditions,the single-photon light detection and ranging(Lidar)technique based on timecorrelated single-photon counting(TCSPC)is suited for collecting a three-dimensional(3D)profile of the target.We present a rapid 3D reconstruction approach for single-photon Lidar with low signal-to-background ratio(SBR)and few photons based on a combination of short-duration range gate selection,photon accumulation of surrounding pixels,and photon efficiency algorithm in this paper.We achieve the best noise filtering and 3D image reconstruction by choosing the optimal combined order of simple methods.Experiments were carried out to validate the various depth estimation algorithms using simulated data and single-photon avalanche diode(SPAD)array data under varying SBR.The experimental results demonstrate that our proposed method can achieve high-quality 3D reconstruction with a faster processing speed compared to the existing algorithms.The proposed technology will encourage the use of single-photon Lidar to suit practical needs such as quick and noise-tolerant 3D imaging.

Decoding algorithms of single photon counting imager based on two-dimensional Vernier anodes

The decoding algorithms of two-dimensional Vernier anodes are deduced theoretically.The precision of decoding and uniqueness of encoding are proved.The influencing factors of detection sensitivity and spatial resolution are discussed.The single photon imaging system is constructed,and the two-dimensional Vernier collector is fabricated.The image of the ultra-weak emission source is reconstructed.The spatial resolution of the system is about 100μm.

基于单像素单光子探测的目标识别与跟踪方法

为了实现弱回波信号下非合作目标识别跟踪,文章基于单像素光子计数激光雷达系统设计了目标识别跟踪策略,并且提出了一种目标识别跟踪方法。该方法首先将单像素光子计数激光雷达系统采集得到的三维点云经过插值处理得到直观的距离像,然后采用最大稳定极值区域算法分割目标和背景,根据目标轮廓特征识别并选择需要跟踪的目标。最后提取识别目标的质心,与激光雷达扫描中心的偏差作为误差信号,控制伺服系统在扫描的基础之上执行目标跟踪。实验结果表明,当激光发射能量为625 pJ、回波光子数为25时,该系统能对距离为5 m、角速度约为2 mrad/s的目标进行稳定的识别跟踪;验证了基于单像素光子计数激光雷达的策略及方法能够稳定的分割目标和背景,以及正确提取需要识别跟踪测距的目标质心,为弱回波信号下目标识别跟踪测距提供一种有效直观的探测方法,同时,弱信号探测作为远距离探测的必要条件,为远距离下的目标探测及识别跟踪提供了一个新的技术方向。

月基极紫外相机光子计数成像探测器Ge膜的空间质子辐照稳定性

光子计数成像探测器是月基极紫外相机等空间成像载荷的核心成像器件。Ge膜作为探测器的电荷感应层,在空间质子辐照环境下的稳定性直接影响系统的成像质量。采用Monte-Carlo法仿真了500 nm Ge膜被10、50和100 keV高能质子辐照后,Ge膜内部的质子浓度分布与空位缺陷分布。仿真结果表明,50 keV质子在Ge膜内部产生的空位缺陷对膜层内部损伤最大。对100、230、350和500 nm厚度Ge膜分别进行50 keV质子辐照实验,经方阻仪测试显示,越厚的薄膜辐照后方阻变化越大,500 nm比100 nm Ge膜方阻增加量高约500 MΩ/。通过原子力显微镜(AFM)表征发现,500 nm Ge膜辐照后出现膜层凸起与分离,均方根表面粗糙度由1.63 nm增至约10 nm。研究结果表明,在满足方阻要求的前提下,通过对Ge膜厚度的合理设计,可以有效减小高能质子辐照带来的损伤。

基于InGaAs单光子探测器的线阵扫描激光雷达及其光子信号处理技术研究

随着探测体系的发展,基于单光子探测技术的光子计数激光雷达受到了广泛关注,有效降低了系统对激光功率的需求,广泛应用在远距离测距及成像领域。针对激光雷达在人眼安全波段的工作需求,基于自由运转模式InGaAs/InP SPAD单光子探测器设计了一套多元收发的远程线阵光子计数激光雷达扫描成像原型系统,对探测器在日光背景下的探测概率影响因素展开了分析,配合主动淬灭电路设计及工作温度、偏压调整获得了系统的最佳工作点,并针对扫描视场中孤立目标特征采用了点云滤波及后脉冲预处理算法,将单个接收通道的原始数据率由200 kbps量级降低至小于1 kbps。与记录单次回波相比,单个测距周期记录四次回波可将有效数据量提升约5%。同时也对探测器的噪声及后脉冲等特性进行了分析。该系统工作波段为1550 nm,探测器线阵规模可达到128元,激光重频为20 kHz,可在2 s内实现水平200°范围内的激光三维成像,作用距离>3 km。经过成像算法处理,该系统在日光条件下成功实现多距离目标三维成像,成像目标清晰。

光子计数集成成像的压缩与重构

集成成像技术作为一种重要的裸眼三维显示技术,在完整记录三维场景信息的同时,庞大的数据量给传输和存储带来了压力。为了实现图像的有效压缩和重构,根据光子计数集成成像的特点,基于分布式压缩感知理论,提出用于图像压缩与重构的方案。该方案将图像分为参考图像和非参考图像两类,对其设置不同的测量率并分别进行重构。为保证非参考图像的重构质量,提出一种联合重构算法。该算法首先对非参考图像进行分块测量,依据与参考图像之间的相关性进行图像块分类,然后结合参考图像测量值信息构建新的测量矢量,利用新的测量矢量完成初次图像重构。为了进一步提升图像重构质量,对初次重构结果进行二次残差补偿重构,获得最终重构结果。最后通过设置不同的测量率进行了大量实验,实验结果表明,所提算法在测量率为0.25时,图像重构质量可以达到30 dB,测量率为0.4时,图像质量可以达到35 dB,算法性能具有一定的优越性。

基于MCP/sCMOS的单光子成像探测系统及算法研究

针对单光子计数成像技术探测目标信号微弱信噪比低、所得图像目标区域不清楚、背景噪声严重等问题。本文利用270±5 nm的日盲紫外滤光片、图像增益7105的微通道板像增强器(MCP)、荧光屏和最大分辨率为1504×1504的科学级互补金属氧化物半导体(sCMOS)等器件,设计了日盲紫外单光子探测系统,并通过时序控制获取了单光子光斑图像。为了突出图像中的目标区域,本文利用改进的形态学高帽变换算法,对光斑目标区域进行增强处理;随后利用三角阈值法对图像进行二值化处理,同时利用连通域对目标区域的坐标进行提取;最后运用区域极值算法在原图中的目标区域进行单光子计数。对紫外光源进行了单次曝光时间为80~100 ns的系列成像和数据处理实验,实验结果验证了所设计的单光子成像探测系统和光子计数算法的可行性。

大型客体光子计数成像技术的发展与挑战

具有光子计数能力的探测器给辐射成像领域带来了技术革新,具有巨大的应用潜力。光子计数探测器凭借其能量分辨能力将有助于提高辐射图像质量、降低辐射剂量、提高检测效率。目前,光子计数成像技术在医学诊断和行包安检等低能领域已有广泛和深入的研究,比如在能谱CT、乳腺检查、PET等领域诞生了许多成果,但是在集装箱检测及车辆安检等大型客体检测的中高能(MeV)领域研究较少,还需进一步克服技术上的困难,以达到中高能射线和高计数率条件的应用要求。本研究重点介绍了光子计数成像技术的特征优势、在X/γ射线医学诊断、安全检查辐射成像系统中的研究现状及面临的挑战,分析了其在大型客体检测中的应用现状和需要进一步突破的技术难点。