Dead time corrections to photon counting statistics II: Quantum theory

The recent formulation of the quantum theory of photodetection, based on the quantum theory of continuous measurements, is extended to the case of a (nonideal) detector which has non-zero dead time. A general result is proven which expresses the dead time modified counting statistics in terms of the counting statistics of anassociated ideal detector. As an illustration, the dead time corrections to the counting statistics of a single-mode free field are worked out, and these corrections are shown to be identical in form to the dead time corrections for a classical optical field of constant intensity.     

Empirical dead‐time corrections for synchrotron sources

An experimental comparison of models for performing dead‐time corrections of photon‐counting detectors at synchrotron sources is presented. The performance of several detectors in the three operating modes of the Advanced Photon Source is systematically compared, with particular emphasis on asymmetric fill patterns. Several simple and well known correction formulas are evaluated. The results demonstrate the critical importance of detector speed and synchrotron fill pattern in selecting the proper dead‐time correction.     

Measurement of X-ray photon energy and arrival time using a silicon drift detector

Detecting the X-ray emission of pulsars and obtaining the photons' time of arrival are the foundational steps in autonomous navigation via X-ray pulsar measurement. The precision of a pulse's time of arrival is mainly determined by the precision of photon arrival time measurement. In this work, a silicon drift detector is used to measure photon energy and arrival time. The measurement system consists of a signal detector, a processing unit, a signal acquisition unit and a data receiving unit. This system acquires the energy resolution and arrival time information of photons. In particular, background noise with different energies disturbs pulse profile forming, the system can also achieve a high signal-to-noise ratio profile. Ground test results show that this system can be applied in autonomous navigation based on X-ray pulsar measurement.     

硅雪崩光电二极管单光子探测器

将硅雪崩光电二极管应用于盖革模式下,制作出高量子效率、低噪音、短死时间的单光子探测器.设计并制作了雪崩抑制电路,获得探测器特性参量为无源抑制方式下死时间1μs,有源抑制下60～80ns,输出脉冲宽度15～20ns.并详细检测了探测器直到液氮温度下的特性.观察到一些新现象.     

用于脉冲星导航的X射线光子计数探测器研究

研制了用于脉冲星导航的X射线光子计数探测器原理样机, 该探测器主要由对X射线灵敏度较高的CsI光电阴极、微通道板电子倍增器和收集阳极组成. 对X射线光子计数探测器灵敏度、时间分辨率和整个系统的死时间进行了测试, 实验结果表明该探测器的灵敏度在5 keV时可达5.2× 10³ A/W, 时间分辨率可达到1.1 ns, 系统整体的死时间为100 ns. 关键词： 脉冲星导航 光子计数探测器 灵敏度 时间分辨率     

超短光脉冲波形对门模单光子探测的影响

采用两种不同的皮秒光脉冲波形进行了门模单光子探测实验.测量了单光子探测效率随探测器和超短脉冲光源之间的同步延迟细微调节时的变化曲线.结果表明：光脉冲波形直接影响光子到达时间与门脉冲时间窗口之间的精确同步和探测效率,使用其中一种脉宽较短的皮秒光脉冲时探测效率比使用另一种脉冲提高了约9%.     

基于单光子探测及脉冲位置调制的激光通信关键技术研究

为了实现高灵敏度的空间激光通信,并提高传输信道的抗干扰能力,将单光子探测技术和脉冲位置调制技术相结合,采用门控电路与反馈淬灭电路相结合的方式淬灭单光子探测器雪崩,设计了插入帧头法用于脉冲位置调制解调。用现场可编程门阵列进行了脉冲位置调制解调过程的仿真,验证了插入帧头法的有效性与可行性。在此基础上搭建了1 550 nm的脉冲位置调制激光通信实验,同时测试了单光子探测器在不同参数下的性能。结果表明,当探测效率为25%,触发延时为8.00 ns,门宽为5.0 ns,死时间为0.1μs时,单光子探测器性能最佳。最后测试了不同调制速率下单光子探测器的探测灵敏度,结果表明,当通信码速率为1 Mbps时,通信灵敏度为-51.8 dBm;当通信码速率为4 Mbps时,通信灵敏度为-41.0 dBm,实现了高灵敏度的空间激光通信。     

利用双光子吸收效应测量激光脉冲的相干时间

研究了利用反向泵浦－探测双光子吸收材料的方法来测量脉冲激光的相干时间，并测量量了２３ｐｓ，５３２ｎｍ Ｎｄ：ＹＡＧ激光脉冲的相干时间。实验和理论分析表明，光束相干作用增加了双光子吸收，利用此方法可测量其它脉宽激光的相干时间。     

基于X射线脉冲星导航的地面模拟系统研究

为进行X射线脉冲星导航的关键技术研究,搭建了基于X射线脉冲星导航的地面模拟系统.地面模拟系统由模拟X射线脉冲源、基于微通道板的高灵敏X射线光子探测器、电荷灵敏前放和主放电路、时间测量单元、X射线脉冲轮廓构造及X射线脉冲到达时间测量系统组成.该模拟系统可在地面模拟X射线脉冲星导航的星源的强度、周期及脉冲轮廓,实现对X射线脉冲星单光子到达时间的记录,构造X射线脉冲星脉冲轮廓,计算X射线脉冲到达时间.描述了基于X射线脉冲星导航的地面模拟系统的组成和工作原理,报道了基于X射线脉冲星导航的地面模拟系统的初步结果. 关键词： X射线脉冲星导航 微通道板光子探测器 脉冲轮廓     

一维游标位敏阳极光子计数探测器

报道了一维游标位敏阳极光子计数探测器,详细介绍了一维游标位敏阳极的解码原理和设计结果.搭建了基于一维游标位敏阳极探测器的紫外光子计数探测系统.该系统工作于光子计数模式,可同时测量单光子事件的一维坐标.获得了对应入射光空间强度一维分布的脉冲计数分布图.通过测试,系统的分辨率优于100μm.该探测器可以实现极微弱的高能光子、电子和离子等粒子流强度分布的一维探测,因此可以用于深空探测、光谱测量、高能物理以及生物发光探测.     

微通道板增益对光子计数探测器成像性能影响

微通道板作为二维位置灵敏阳极光子计数探测器中的电子倍增器件,其增益特性直接影响探测器的成像性能。搭建了系统测试平台,测量了微通道板的增益随电压变化曲线,并获得了3块微通道板叠加后的脉冲高度分布曲线。根据测试结果以及脉冲高度分布曲线的能量分辨率与探测器增益的均匀性之间的物理关系,选择合适电压值和增益对探测器的性能进行优化,探测器分辨率由3.56 lp/mm 提高到4.49 lp/mm ,获得了清晰图像,为探测器的研制提供了技术支持。     

单光子探测技术

近年来,以量子密钥分配为代表的各种量子信息技术应用获得了飞速发展,这些应用对单光子探测器的性能提出了非常苛刻的要求,以光电倍增管和雪崩光电二极管为代表的传统单光子探测器件已经无法满足需求。在此背景下,出现了以超导单光子探测器为代表的新型低温单光子探测器件,其性能比现有商用单光子探测器有了本质性的提升。本文综述了迄今为止各种类型的单光子探测器,并指出各自在量子信息技术应用中的优势和不足之处以及发展方向。     

Dead time correction of photon correlation functions

The dynamic range of single photon counting measurements in quasi elastic light scattering is restricted by detector and counter dead time effects. While distortions of single interval statistics have been treated at great length, only lowest order corrections or very special cases of dead time effects on temporal correlation functions were computed in the past.Dead times result in a direct distortion of correlograms on time scales comparable to the dead time. This effect exists even at low count-rates. It is independent of the count rate for paralyzable systems. Nonparalyzable systems show a count rate dependence with increasing correlation times at high count rates.Furthermore, counting saturation produces additional distortions extending to all lag times. These distortions are computed for the rather general case of -distributed intensities with arbitrary shape of the photon correlation function. Such signals are commonly found in multiparticle homodyne experiments with a finite size detector, i.e. arbitrary value of the intercept or contrast of the correlogram. Exact results are provided for the paralyzable system including the effect of fluctuating dead times. The latter case is then used to compute a useful approximation for nonparalyzable systems as well.     

Energy‐dependent dead‐time correction in digital pulse processors applied to silicon drift detector's X‐ray spectra

Dead‐time effects in X‐ray spectra taken with a digital pulse processor and a silicon drift detector were investigated when the number of events at the low‐energy end of the spectrum was more than half of the total, at counting rates up to 56 kHz. It was found that dead‐time losses in the spectra are energy dependent and an analytical correction for this effect, which takes into account pulse pile‐up, is proposed. This and the usual models have been applied to experimental measurements, evaluating the dead‐time fraction either from the calculations or using the value given by the detector acquisition system. The energy‐dependent dead‐time model proposed fits accurately the experimental energy spectra in the range of counting rates explored in this work. A selection chart of the simplest mathematical model able to correct the pulse‐height distribution according to counting rate and energy spectrum characteristics is included.     

Sub‐microsecond‐resolved multi‐speckle X‐ray photon correlation spectroscopy with a pixel array detector

Small‐angle X‐ray photon correlation spectroscopy (XPCS) measurements spanning delay times from 826 ns to 52.8 s were performed using a photon‐counting pixel array detector with a dynamic range of 0–3 (2 bits). Fine resolution and a wide dynamic range of time scales was achieved by combining two modes of operation of the detector: (i) continuous mode, where data acquisition and data readout are performed in parallel with a frame acquisition time of 19.36 µs, and (ii) burst mode, where 12 frames are acquired with frame integration times of either 2.56 µs frame^?1 or 826 ns frame^?1 followed by 3.49 ms or 1.16 ms, respectively, for readout. The applicability of the detector for performing multi‐speckle XPCS was demonstrated by measuring the Brownian dynamics of 10 nm‐radius gold and 57 nm‐radius silica colloids in water at room temperature. In addition, the capability of the detector to faithfully record one‐ and two‐photon counts was examined by comparing the statistical distribution of photon counts with expected probabilities from the negative binomial distribution. It was found that in burst mode the ratio of 2 s to 1 s is markedly smaller than predicted and that this is attributable to pixel‐response dead‐time.     

单光子探测器量子效率绝对自身标定方案

参考已有的方案,提出了一种更简单的方案来实现单光子探测器量子效率的绝对自身标定。我们利用同轴线缆和数据采集卡代替已有方案中的符合测量电路和计数器,通过精确设定同轴线缆的长度,利用电脉冲在同轴线缆的短路终端反射回波的特性,对一个测量周期中单个脉冲和连续两个脉冲进行区分,用数据采集卡记录区分结果,分别得到探测器探测到两个孪生光子的计数和仅探测到其中任意一个光子的计数,从而算出单光子探测器的量子效率。此方案不需要其他任何的参考标准或者另一个探测器.     

基于光电双开关的单光子同步探测

提出了一种基于光电双开关进行同步测量单光子的方法.这种测量方法能够有效抑制背景光以及由背景光引起的后脉冲和死时间对单光子测量的影响,有效地减少了单光子探测中的误计数,改善了单光子测量的信噪比.同时,避免了单光子探测器通常工作在门控电压方式下产生自发光子辐射的缺点.     

Dead time corrections to photon counting statistics I: Classical theory

A complete solution is given to the problem of calculating the dead time corrections to the counting statistics of an arbitrary doubly stochastic Poisson process with a non-negative random intensity function. It is shown that for the particular case of an optical field with constant intensity, the general dead time modified counting formula leads to a corrected version of results earlier derived by Bedard.     

The EIGER detector for low‐energy electron microscopy and photoemission electron microscopy

EIGER is a single‐photon‐counting hybrid pixel detector developed at the Paul Scherrer Institut, Switzerland. It is designed for applications at synchrotron light sources with photon energies above 5 keV. Features of EIGER include a small pixel size (75 µm × 75 µm), a high frame rate (up to 23 kHz), a small dead‐time between frames (down to 3 µs) and a dynamic range up to 32‐bit. In this article, the use of EIGER as a detector for electrons in low‐energy electron microscopy (LEEM) and photoemission electron microscopy (PEEM) is reported. It is demonstrated that, with only a minimal modification to the sensitive part of the detector, EIGER is able to detect electrons emitted or reflected by the sample and accelerated to 8–20 keV. The imaging capabilities are shown to be superior to the standard microchannel plate detector for these types of applications. This is due to the much higher signal‐to‐noise ratio, better homogeneity and improved dynamic range. In addition, the operation of the EIGER detector is not affected by radiation damage from electrons in the present energy range and guarantees more stable performance over time. To benchmark the detector capabilities, LEEM experiments are performed on selected surfaces and the magnetic and electronic properties of individual iron nanoparticles with sizes ranging from 8 to 22 nm are detected using the PEEM endstation at the Surface/Interface Microscopy (SIM) beamline of the Swiss Light Source.     

单分子光子源光子统计的非平衡探测

研究了在Hanbury Brown Twiss探测方式下，非平衡探测系统对光子统计测量的影响。通过记录2个单光子计数器响应的单分子光子源输出的每一个事件，分析具有泊松统计背景的实际单分子光子源的光子统计特性，讨论并给出了非平衡探测系统的单分子光子源Mandel参数。研究表明：非理想的50／50分束器、非理想的线性传输效率和非理想的探测器都会使单分子光子源Mandel参数的实际测量结果小于平衡系统的Mandel参数，最后给出了单分子光子源Mandel参数的非理想探测的校正表达式。