Opto-electronic high-frequency cross-correlation using avalanche photodiodes

Correlation analysis has become an important research tool in the investigation of signals and systems behaviour. We report on a special opto-electronic cross-correlator in which a silicon avalanche photodiode is used as the main component. The internal gain of this photodiode is pulse-modulated with 330 ps FWHM at 126 MHz repetition rate, or is modulated sinusoidally at frequencies of up to 882 MHz, respectively. In the pulsed mode, very weak repetitive optical pulses can be detected with 3 × 10⁻³ photons per pulse sensitivity, and with 10 ps timing accuracy. The second mode offers time-selective signal rejection capabilities with 3 ps time resolution. The opto-electronic cross-correlator can be used in displacement and distance measurement, robotics, time dispersion analysis in optical fibres, transient absorption spectroscopy, fluorescence decay measurement, lifetime-selective fluorescence detection, and in fluorescence signal suppression in Raman spectroscopy.     

Time interval measurement device based on surface acoustic wave filter excitation, providing 1 ps precision and stability

This article deals with the time interval measurement device, which is based on a surface acoustic wave (SAW) filter as a time interpolator. The operating principle is based on the fact that a transversal SAW filter excited by a short pulse can generate a finite signal with highly suppressed spectra outside a narrow frequency band. If the responses to two excitations are sampled at clock ticks, they can be precisely reconstructed from a finite number of samples and then compared so as to determine the time interval between the two excitations. We have designed and constructed a two-channel time interval measurement device which allows independent timing of two events and evaluation of the time interval between them. The device has been constructed using commercially available components. The experimental results proved the concept. We have assessed the single-shot time interval measurement precision of 1.3 ps rms that corresponds to the time of arrival precision of 0.9 ps rms in each channel. The temperature drift of the measured time interval on temperature is lower than 0.5 ps/K, and the long term stability is better than +/-0.2 ps/h. These are to our knowledge the best values reported for the time interval measurement device. The results are in good agreement with the error budget based on the theoretical analysis.     

一种具有优良分辨力、线性及温度稳定性的量化时延的产生方法

目前的很多仪器设备中需要分辨率优于ns量级的时间量化仪和延迟单元.研究了利用信号在传输时的延迟来进行时间量化的可行性及其特点.实验结果表明基于传输延迟的时间量化技术较国外报道的基于CMOS门延迟的时间量化技术有线性度好、温度稳定性好、结构简单、实现容易等特点.采用导线延迟技术实现了一个分辨率优于300 ps,量化范围优于2 ns的时间量化仪.它的特点是延迟线后级检测电路参数的差异对这种设计有影响,必须经过标定,经过标定之后对某些特殊点的时间量化精度可达12 ps.同时指出了当提高分辨率时面临的问题以及基于ASIC技术的解决方法.     

Fully programmable single-photon detection module for InGaAs/InP single-photon avalanche diodes with clean and sub-nanosecond gating transitions

We present the design and characterization of a modern near-infrared photon counting module, able to exploit the best performance of InGaAs/InP single-photon avalanche diodes for the detection of fast and faint optical signals up to 1.7 μm. Such instrument is suitable for many applications, thanks to the user-friendly interface and the fully adjustable settings of all operating parameters. We extensively characterized both the electronics and the detector, and we validated such instrument up to 133 MHz gate repetition frequency, for photon-counting and photon-timing applications, with very clean temporal response and excellent timing performance of less than 100 ps.     

多通道高精度时间-数字转换器的研制

介绍了一种基于USB2.0接口的多通道高精度时间 数字转换器(time-to-digital converter, TDC)的设计与实现。完成了NIM-LVPECL电平转换电路、高速串并转换电路、基于FPGA的数据处理及相关逻辑控制等单元电路的设计,最后给出了TDC的测试性能指标。结果表明,TDC的最小时间分辨率为403 ps,测量时间范围为0~420 us,测量“死时间”<13 ns。TDC可广泛应用于高精度的时间间隔测量领域,特别是作为飞行时间质谱仪（time-of-flight mass spectrometer, TOF-MS）的数据采集卡。     

Gamma bang time analysis at OMEGA

Absolute bang time measurements with the gas Cherenkov detector (GCD) and gamma reaction history (GRH) diagnostic have been performed to high precision at the OMEGA laser facility at the University of Rochester with bang time values for the two diagnostics agreeing to within 5 ps on average. X-ray timing measurements of laser-target coupling were used to calibrate a facility-generated laser timing fiducial with rms spreads in the measured coupling times of 9 ps for both GCD and GRH. Increased fusion yields at the National Ignition Facility (NIF) will allow for improved measurement precision with the GRH easily exceeding NIF system design requirements.     

Subnanosecond single photon counting fluorescence spectroscopy using synchronously pumped tunable dye laser excitation

A synchronously pumped tunable dye laser has been constructed and interfaced with a modified Ortec 9200 photon counting system for the purpose of measuring subnanosecond relaxation phenomena. The dye laser excitation pulse, which has an intrinsic 35-ps FWHM for Rhodamine 6G, is 350 ps when measured by time-correlated single photon counting. This value appears to be characteristic of the transit time jitter in the RCA 8850 photomultiplier tube. Subnanosecond fluorescence lifetimes of Rhodamine B with KI as a quencher have been determined by deconvolution of photons counted versus elapsed time using the method of moments; the shortest lifetime measured was 68 ps. Various technical aspects of the system are discussed with emphasis on applications to biophysical problems.     

用于激光测距的高精度时间数字转换电路

针对大容量现场可编程门阵列(FPGA)时间数字转换电路线性度较差的问题,采用小容量FPGA实现了用于激光测距的高精度、高线性度时间数字转换电路。通过对高速计数器、数字插入方法、编码器硬件算法的研究,分析了影响时间数字转换电路精度和非线性误差的因素,提出了一种降低非线性误差的方法。首先,根据所分析的影响因素,解决了高速锁存的问题,在单片小容量FGPA XC2V250上实现了时间数字转换电路;接着,通过USB接口将携带时间信息的计数器值和温度计码转为二进制编码值传给PC机,进行计算和显示;最后,设计了延时测量电路,对所设计的时间数字转换电路进行了测试,得到了各个延时单元延时的大小,并进行了数据分析和处理。测试结果显示:时间数字转换电路单次测时分辨率约为80 ps,校正后可达40 ps左右,微分非线性误差为-0.524LSB~+0.448LSB,积分非线性误差为-1.598LSB~+1.492LSB,可以满足飞行时间法激光测距中高精度测时的要求。     

时频测量高性能内插模块实现

精密时间间隔测量技术在许多重要领域都占据着十分重要的地位,本文实现了一种基于时间幅度转换法的高分辨力、高单次测量精密度、高采样率时间内插模块并应用于高精度时间间隔测量,其时间分辨力达到20ps以内,单次测量精密度优于8ps,采样率达到了8MHz。     

Subnanosecond time-correlated photon counting with tunable lasers

We present several laser based methods to improve the technique of time-correlated photon counting. Our Ar(+) laser pumped tunable dye laser can be operated in three timing configurations: acousto-optically mode locked, cavity dumped, and cavity dumped-mode locked. Performance characteristics of the laser system in various operational modes are described along with measurement techniques for both gas and liquid phase. The subnanosecond pulses generated by mode locking are extremely stable and they maintain identical pulse shapes over a 6-h period, as shown via photon counting measurements at a 15-psec channel resolution. Our RCA C31034 photomultiplier with a red sensitive GaAs photocathode provides wavelength-independent response to detected fluorescence in both the visible and ultraviolet. The present limit of our apparatus is controlled by the accuracy of deconvoluting fluorescence decay from the finite response width caused by photomultiplier transit time dispersion (0.8 nsec FWHM). Our system stability is sufficient to accurately determine exponential decays as short as 50 psec. Furthermore, we can successfully analyze dual exponential decays such as those arising from solution reorientation times of 390 psec competing with a fluorescence lifetime of 725 psec. Examples of the laser performance are selected from a variety of measurements in the gas phase and from the fluorescent dye rose bengal in the liquid phase.     

Self-suppression of reset induced triggering in picosecond SPAD timing circuits

We present a new photon timing circuit that achieves a time resolution of 35 ps full width at half maximum with single photon avalanche diodes having active area diameters up to 200 microm. The timing circuit is based on a double avalanche current sensing network that makes it particularly suited to operation at high photon counting rates. Thanks to its self-adjusting capabilities, no trimming is needed even when changing the photodetector operating conditions over a wide range.     

A photoelectron-photoion coincidence imaging apparatus for femtosecond time-resolved molecular dynamics with electron time-of-flight resolution of sigma=18 ps and energy resolution Delta E/E=3.5%

We report on the construction and performance of a novel photoelectron-photoion coincidence machine in our laboratory in Amsterdam to measure the full three-dimensional momentum distribution of correlated electrons and ions in femtosecond time-resolved molecular beam experiments. We implemented sets of open electron and ion lenses to time stretch and velocity map the charged particles. Time switched voltages are operated on the particle lenses to enable optimal electric field strengths for velocity map focusing conditions of electrons and ions separately. The position and time sensitive detectors employ microchannel plates (MCPs) in front of delay line detectors. A special effort was made to obtain the time-of-flight (TOF) of the electrons at high temporal resolution using small pore (5 microm) MCPs and implementing fast timing electronics. We measured the TOF distribution of the electrons under our typical coincidence field strengths with a temporal resolution down to sigma=18 ps. We observed that our electron coincidence detector has a timing resolution better than sigma=16 ps, which is mainly determined by the residual transit time spread of the MCPs. The typical electron energy resolution appears to be nearly laser bandwidth limited with a relative resolution of DeltaE(FWHM)/E=3.5% for electrons with kinetic energy near 2 eV. The mass resolution of the ion detector for ions measured in coincidence with electrons is about Deltam(FWHM)/m=14150. The velocity map focusing of our extended source volume of particles, due to the overlap of the molecular beam with the laser beams, results in a parent ion spot on our detector focused down to sigma=115 microm.     

Custom single-photon avalanche diode with integrated front-end for parallel photon timing applications

Emerged as a solid state alternative to photo multiplier tubes (PMTs), single-photon avalanche diodes (SPADs) are nowadays widely used in the field of single-photon timing applications. Custom technology SPADs assure remarkable performance, in particular a 10 counts/s dark count rate (DCR) at low temperature, a high photon detection efficiency (PDE) with a 50% peak at 550 nm and a 30 ps (full width at half maximum, FWHM) temporal resolution, even with large area devices, have been obtained. Over the past few years, the birth of novel techniques of analysis has led to the parallelization of the measurement systems and to a consequent increasing demand for the development of monolithic arrays of detectors. Unfortunately, the implementation of a multidimensional system is a challenging task from the electrical point of view; in particular, the avalanche current pick-up circuit, used to obtain the previously reported performance, has to be modified in order to enable high parallel temporal resolution, while minimizing the electrical crosstalk probability between channels. In the past, the problem has been solved by integrating the front-end electronics next to the photodetector, in order to reduce the parasitic capacitances and consequently the filtering action on the current signal of the SPAD, leading to an improvement of the timing jitter at higher threshold. This solution has been implemented by using standard complementary metal-oxide-semiconductor (CMOS) technologies, which, however, do not allow a complete control on the SPAD structure; for this reason the intrinsic performance of CMOS SPADs, such as DCR, PDE, and afterpulsing probability, are worse than those attainable with custom detectors. In this paper, we propose a pixel architecture, which enables the development of custom SPAD arrays in which every channel maintains the performance of the best single photodetector. The system relies on the integration of the timing signal pick-up circuit next to the photodiode, achieved by modifying the technological process flow used for the fabrication of the custom SPAD. The pixel is completed by an external standard CMOS active quenching circuit, which assures stable timing performance at quite high count rate (>1 MHz).     

Algorithm for precision subsample timing between Gaussian-like pulses

Moderately priced oscilloscopes available for the NIF power sensors and target diagnostics have 6 GHz bandwidths at 20-25 Gsamples/s (40 ps sample spacing). Some NIF experiments require cross timing between instruments be determined with accuracy better than 30 ps. A simple analysis algorithm for Gaussian-like pulses such as the 100-ps-wide NIF timing fiducial can achieve single-event cross-timing precision of 1 ps (1/50 of the sample spacing). The midpoint-timing algorithm is presented along with simulations that show why the technique produces good timing results. Optimum pulse width is found to be ～2.5 times the sample spacing. Experimental measurements demonstrate use of the technique and highlight the conditions needed to obtain optimum timing performance.     

Digital-signal-processor-based dynamic imaging system for optical tomography

In this article, we introduce a dynamic optical tomography system that is, unlike currently available analog instrumentation, based on digital data acquisition and filtering techniques. At the core of this continuous wave instrument is a digital signal processor (DSP) that collects, collates, processes, and filters the digitized data set. The processor is also responsible for managing system timing and the imaging routines which can acquire real-time data at rates as high as 150 Hz. Many of the synchronously timed processes are controlled by a complex programmable logic device that is also used in conjunction with the DSP to orchestrate data flow. The operation of the system is implemented through a comprehensive graphical user interface designed with LABVIEW software which integrates automated calibration, data acquisition, data organization, and signal postprocessing. Performance analysis demonstrates very low system noise (approximately 1 pW rms noise equivalent power), excellent signal precision (<0.04%-0.2%) and long term system stability (<1% over 40 min). A large dynamic range (approximately 190 dB) accommodates a wide scope of measurement geometries and tissue types. First experiments on tissue phantoms show that dynamic behavior is accurately captured and spatial location can be correctly tracked using this system.     

Continuous measurement of the arrival times of x-ray photon sequence

In order to record x-ray pulse profile for x-ray pulsar-based navigation and timing, this paper presents a continuous, high-precision method for measuring arrival times of photon sequence with a common starting point. In this method, a high stability atomic clock is counted to measure the coarse time of arrival photon. A high resolution time-to-digital converter is used to measure the fine time of arrival photon. The coarse times and the fine times are recorded continuously and then transferred to computer memory by way of memory switch. The pulse profile is obtained by a special data processing method. A special circuit was developed and a low-level x-ray pulse profile measurement experiment system was setup. The arrival times of x-ray photon sequence can be consecutively recorded with a time resolution of 500 ps and the profile of x-ray pulse was constructed. The data also can be used for analysis by many other methods, such as statistical distribution of photon events per time interval, statistical distribution of time interval between two photon events, photon counting histogram, autocorrelation and higher order autocorrelation.     

高分辨SPI/TOFMS的研制及VOCs分子式确定

单光子能量10.6eV的真空紫外灯可电离大部分的挥发性有机物,生成分子离子,几乎无碎片,谱图简单。本文介绍了实验室自制的真空紫外灯单光子电离反射式飞行时间质谱仪的原理、仪器结构及初步结果。测试仪器分辨率超过4000(FWHM),质量精度优于6ppm。苯的检出限可至52ppbv。将仪器用于香烟烟气和聚氯乙烯(PVC)热解产物的检测。结果表明,单光子软电离源与高分辨质谱的结合,可直接用于复杂挥发性有机物(VOCs)分子式的确定。     

基于Cortex-M3的快速发光二极管光电参数测量系统

针对发光二极管（LED）分选设备对光电参数测量系统的需求,研制了一种基于Cortex-M3（以下简称M3）的快速LED光电参数（包括光参数和电参数两部分）测量系统。该系统分为光参数检测模块（自制光谱仪）、电参数测量模块及显示模块等3部分。光参数检测模块采用M3作为主处理器,对测量获得的光谱数据进行计算,进而得出实测的LED光参数,并将光参数传递给同样以M3为主处理器的电参数测量模块。利用该系统架构,有效提高了LED参数测量的速度和性能。最后,在脱离LED分选机械控制的前提下,利用研制的LED光电参数测量系统进行了LED的实际快速测量。结果显示：电参数测量周期小于31 ms,光参数测量周期可小至10 ms,色坐标一致性误差小于0.002 5%。     

Note: Optical trigger device with sub-picosecond timing jitter and stability

We are presenting the design, construction, and overall performance of the optical trigger device. This device generates an electrical signal synchronously to the detected ultra-short optical pulse. The device was designed for application in satellite laser ranging and laser time transfer experiments, time correlated photon counting and similar experiments, where picosecond timing resolution and detection delay stability are required. It consists of the ultrafast optical detector, signal discriminator, output pulse forming circuit, and output driver circuits. It was constructed as a single compact device to optimize their matching and maintain stability. The detector consists of an avalanche photodiode--both silicon and germanium types may be used to cover the wavelength range of 350-1550 nm. The analogue signal of this photodiode is sensed by the ultrafast comparator with 8 GHz bandwidth. The ps clock distribution circuit is used to generate the fast rise/fall time output pulses of pre-set length. The trigger device timing performance is excellent: the random component of the timing jitter is typically 880 fs, the temperature dependence of the detection delay was measured to be 370 fs/K. The systematic error contribution depends on the laser used and its stability. The sub-ps values have been obtained for various laser sources.     

A source of a reference spherical wave based on a single mode optical fiber with a narrowed exit aperture

A new type of a reference spherical wave source (SWS) based on a single mode optical fiber with a narrowed down up to the submicrometer size exit aperture is proposed. It is intended for the precision point diffraction interferometers as a source of a reference wave. Systematic experimental errors which influence the measurement accuracy of the quality of the wave fronts generated by the SWSs are considered. Experimental data on wave front deformations are given. The combined root-mean-square (rms) wave deformation for a couple of the SWSs measured in a numerical aperture of NA=0.27 reaches the value of rms=0.36 nm that corresponds to rms=0.25 nm of a single SWS or about lambda2500 for the red He-Ne laser.