强荧光背景环境中荧光涨落谱--蒙特卡罗模拟研究

荧光涨落谱方法(Fluorescence Fluctuation Spectroscopy)通过分析微小探测区域内的荧光涨落信号,获得粒子亮度、扩散系数以及溶液浓度等信息。利用Monte Carlo模拟方法,研究了溶液中自荧光背景和系统噪声对荧光涨落谱的影响。结果表明,利用双组分光子计数统计方法,可以有效去除低亮度、高浓度背景组分自荧光和均匀分布系统噪声产生的影响。本结果为利用荧光涨落谱方法测量细胞体系复杂环境中的蛋白质相互作用提供帮助。     

Photon counts modulation in optical time domain reflectometry

The quantum fluctuation of photon counting limits the field application of optical time domain reflection. A method of photon counts modulation optics time domain reflection with single photon detection at 1.55 μm is presented. The influence of quantum fluctuation can be effectively controlled by demodulation technology since quantum fluctuation shows a uniform distribution in the frequency domain. Combined with the changing of the integration time of the lock-in amplifier, the signal to noise ratio is significantly enhanced. Accordingly the signal to noise improvement ratio reaches 31.7 dB compared with the direct photon counting measurement.     

Photon-in/photon-out endstation for studies of energy materials at beamline 02B02 of Shanghai Synchrotron Radiation Facility

A new photon-in/photon-out endstation at beamline 02B02 of the Shanghai Synchrotron Radiation Facility for studying the electronic structure of energy materials has been constructed and fully opened to users. The endstation has the capability to perform soft x-ray absorption spectroscopy in total electron yield and total fluorescence yield modes simultaneously. The photon energy ranges from 40 eV to 2000 eV covering the K-edge of most low Z-elements and the L-edge of 3d transition-metals. The new self-designed channeltron detector allows us to achieve good fluorescence signals at the low photon flux. In addition, we synchronously collect the signals of a standard reference sample and a gold mesh on the upstream to calibrate the photon energy and monitor the beam fluctuation, respectively. In order to cross the pressure gap,in situ gas and liquid cells for soft x-ray absorption spectroscopy are developed to study the samples under realistic working conditions.     

Fluorescence fluctuation spectroscopy in subdiffraction focal volumes

We establish fluorescence fluctuation spectroscopy (FFS) with nanoscale detection volumes generated by stimulated emission depletion. Our method applies fluorescence correlation spectroscopy and fluorescence intensity distribution analysis to extract molecular information about mobilities and fluorescence emission in solution. The combination of correlation analysis with that of photon intensity distributions reveals a fivefold squeezing of the detection volume over current diffraction-limited systems, which is in full agreement with the simultaneously demonstrated 25-fold reduction in (axial) focal transit time. Our method significantly extends the potential of far-field FFS, including for the noninvasive investigation of molecular reactions at higher concentrations.     

What are the correct L‐subshell photoionization cross sections for quantitative X‐ray spectroscopy?

For fundamental parameter‐based, quantitative X‐ray fluorescence, X‐ray photoelectron spectroscopy or Auger electron spectroscopy, it is crucial to accurately know the photoionization cross sections (PCS). This atomic probability to absorb the exciting photon and eject a photoelectron, in general, followed by a subsequent decay resulting in the emission of a fluorescence photon or an Auger electron, strongly depends on the electron configuration and photon energy. Two contrary models for the photon energy dependence of the L‐subshell PCS, or the 2s, 2p ½ and 2p 3/2; energy levels, respectively, exist in the literature, and an experimental verification was not available until recently. In this work, the two models for calculating the PCS are discussed, and their influence on quantitative experiments is demonstrated by means of the fluorescence production cross sections for the three L shells. Depending on the excitation conditions, these fluorescence production cross sections and, thus, the derived quantitative results can differ significantly if the wrong PCS model is employed. Copyright © 2016 John Wiley & Sons, Ltd.     

Theoretical study on single-molecule spectroscopy

The photon-by-photon approach for single molecule spectroscopy experiments utilizes the information carried by each detected photon and allows the measurements of conformational fluctuation with time resolution on a vast range of time scales, where each photon represents a data point. Here, we theoretically simulate the photon emission dynamics of a single molecule spectroscopy using the kinetic Monte Carlo algorithm to understand the underlying complex photon dynamic process of a single molecule. In addition, by following the molecular process in real time, the mechanism of complex biochemical reactions can be revealed. We hope that this theoretical study will serve as an introduction and a guideline into this exciting new field.     

Fast, flexible algorithm for calculating photon correlations

We introduce a new algorithm for computing correlations of photon arrival time data acquired in single-molecule fluorescence spectroscopy and fluorescence correlation spectroscopy (FCS). The algorithm is based on rewriting the correlation as a counting operation on photon pairs and can be used with arbitrary bin widths and spacing. The flexibility of the algorithm is demonstrated by use of FCS simulations and single-molecule photon antibunching experiments. Execution speed is comparable to the commonly used multiple-tau correlation technique. Wide bin spacings are possible that allow for real-time software calculation of correlations, even for high count rates.     

光子计数深度获取系统误差机理研究和矫正

采用两路光子时间到达点构建光纤式光子计数伪随机码深度获取系统.为了研究降低深度误差的方法,以高斯函数为激光回波脉冲,计算瞬时概率密度函数,引入"时间行走"效应数学模型,推导深度误差克拉美罗下限.随着激光回波能量的增大,深度误差先降低再增大,并且码长越长,深度误差越小.采用理论推导的累积分布函数,生成光子时间到达点,蒙特卡洛仿真伪随机序列光子探测过程,结果大于理论数值模拟,符合克拉美罗下界原理.17组标定实验表明:由于目标表面特性的不同而导致探测到激光回波中光子数的浮动,该浮动引发光子"时间行走"效应,并带来伪随机码深度获取系统的互相关函数的整体偏移.采用数值拟合方程拟合不同光子计数比例值下的深度误差,测量得到的光子计数比例值,代入拟合的矫正方程,矫正后的深度均方误差下降至1cm.     

Electron-Impact Induced Molecular Fluoresence Spectroscopy

Abstract

By the bombardment of gaseous molecules with monoenergetic electrons the molecules can be electronically excited and/or fragmented, depending upon the energy supplied by the electrons. Any fragments which may be produced also have the possibility of being produced in electronically (as well as vibrationally and rotationally) excited states. The electronically excited molecules and fragments both possess the possibility of radiative decay (fluorescence). The measurement of this fluorescence as a function of both electron energy and photon wavelength is termed “electron-impact induced fluorescence spectroscopy.” A plot of fluorescence intensity as a function of the electron energy at a given photon wavelength is generally referred to as an “excitation function,” which is exactly analogous to the excitation spectrum which can be obtained in conventional (optically excited) fluorescence spectrometry. A plot of the fluorescence intensity as a function of photon wavelength at a given electron energy is termed the “fluorescence spectrum.” A three dimensional plot of the fluorescence intensity as a function of both the photon wavelength and the electron energy may also be constructed, and is referred to as an “excitation contour plot.”     

Investigation of ultrafast dynamics of CdTe quantum dots by femtosecond fluorescence up-conversion spectroscopy

The ultrafast carrier relaxation processes in CdTe quantum dots are investigated by femtosecond fluorescence upconversion spectroscopy.Photo-excited hole relaxing to the edge of the forbidden gap takes a maximal time of ～ 1.6 ps with exciting at 400 nm,depending on the state of the photo-excited hole.The shallow trapped states and deep trap states in the forbidden gap are confirmed for CdTe quantum dots.In addition,Auger relaxation of trapped carriers is observed to occur with a time constant of ～ 5 ps.A schematic model of photodynamics is established based on the results of the spectroscopy studies.Our work demonstrates that femtosecond fluorescence up-conversion spectroscopy is a suitable and effective tool in studying the transportation and conversion dynamics of photon energy in a nanosystem.     

Identification of single fluorescently labelled mononucleotide molecules in solution by spectrally resolved time-correlated single-photon counting

We describe a method to identify single dye-labelled mononucleotide molecules in solution with high classification probability based on confocal microscopy in combination with spectrally and time-resolved fluorescence detection with two detectors. For efficient excitation of the labelled mononucleotide molecules JA133-dUTP, JA169-dUTP, Cy5-dCTP, and JA242-dUTP a short-pulse diode laser emitting at 634 nm with a repetition rate of 64 MHz was applied. The time-resolved fluorescence signals of individual molecules were analyzed and identified by a maximum likelihood estimator (MLE). Scatter plots of spectrally and time-resolved fluorescence data demonstrated the existence of four distinct populations with symmetrical shape. The distributions of each of the mononucleotide conjugates were determined by fitting a superposition of two independent Gaussians. Taking only those single-molecule bursts which contain more than 50 photon counts, three labelled mononucleotide molecules were identified in solution by spectrally and time-resolved fluorescence spectroscopy with a probability of correct classification of ≈99%. Received: 31 March 2000 / Revised version: 31 May 2000 / Published online: 13 September 2000     

Observation and characterization of the fluorescence decay of the 2s2p(6)np 1P(o) excited states of Ne

Fluorescence decay of the 2s2p(6)np (1)P(o) excited states of neon has been observed directly for the first time. This process has also been observed indirectly by threshold photoelectron spectroscopy and in electron/photon coincidences. The measurements have allowed this weak decay channel to be characterized and branching ratios derived. The fluorescence excitation spectrum is well described by a simple Rydberg model that highlights the interplay and competition between the decay channels of autoionization and fluorescence.     

利用多像素光子计数器的光学串话效应提高光子探测效率

通过分析多像素光子计数器(MPPC)的工作原理和其光学串话(OC)效应的特点,提出在使用MPPC输出雪崩信号的幅度或电荷量作为光子计数的参量时,利用MPPC的OC效应能提高MPPC的光子探测效率的观点,并从理论上分析了OC效应对光子探测效率的影响。理论分析结果显示,在这两种光子计数模式下,利用OC效应能明显提高MPPC的光子探测效率。利用本文模型计算得出当MPPC的雪崩单元数M为1 600个,忽略OC效应时的光子探测效率等于30%,光学串话概率等于50%,以及单脉冲入射光子数均值为10时,包含OC效应影响的等效光子探测效率可提高50%,达45%左右。该结果对MPPC在天体物理、粒子物理、荧光光谱探测等弱光探测场合的应用有一定指导意义。     

Numerical analysis of In0.53Ga0.47As/InP single photon avalanche diodes

A rigorous theoretical model for In 0.53 Ga 0.47 As/InP single photon avalanche diode is utilized to investigate the dependences of single photon quantum efficiency and dark count probability on structure and operation condition.In the model,low field impact ionizations in charge and absorption layers are allowed,while avalanche breakdown can occur only in the multiplication layer.The origin of dark counts is discussed and the results indicate that the dominant mechanism that gives rise to dark counts depends on both device structure and operating condition.When the multiplication layer is thicker than a critical thickness or the temperature is higher than a critical value,generation-recombination in the absorption layer is the dominative mechanism;otherwise band-to-band tunneling in the multiplication layer dominates the dark counts.The thicknesses of charge and multiplication layers greatly affect the dark count and the peak single photon quantum efficiency and increasing the multiplication layer width may reduce the dark count probability and increase the peak single photon quantum efficiency.However,when the multiplication layer width exceeds 1 μm,the peak single photon quantum efficiency increases slowly and it is finally saturated at the quantum efficiency of the single photon avalanche diodes.     

A review of X-ray intensity fluctuation spectroscopy

This article reviews the literature on X-ray fluctuation intensity spectroscopy or, as it is often called, X-ray photon correlation spectroscopy. It highlights measurements using different types of diffuse scattering. To cite this article: M. Sutton, C. R. Physique 9 (2008).     

Photon-number-resolving detection at 1.04 μm via coincidence frequency upconversion

We demonstrate photon-number-resolving detection based on coincidence frequency upconversion. Pumped by synchronized pulses, the photon signal of the coherent state at 1.04 μm was upconverted into visible replicas with preserved photon number distribution. The upconverted photons were then registered by a silicon multipixel photon counter. The photon-number-resolving performance was improved by reducing the background counts with a synchronous pump as the coincidence gate and reducing the intrinsic parametric fluorescence influence with long-wavelength pumping. A total detection efficiency of 3.7% was achieved with a quite low noise probability per pulse of 0.0002.     

Measurement of surface concentration of fluorophores by fluorescence fluctuation spectroscopy

Fluorescence fluctuation spectroscopy is applied to study molecules passing through a small observation volume, usually subjected to diffusive or convective motion in a liquid phase. We suggest that such a technique could be used to measure the areal absolute concentration of fluorophores deposited on a substrate or embedded in a thin film, with a resolution of a few micrometers. The principle is to translate the solid substrate in front of a confocal fluorescence microscope objective and to record the subsequent fluctuations of the fluorescence intensity. The validity of this concept is investigated on model substrates (fluorescent microspheres) and DNA biochips.     

时间相关单光子计数光谱仪的优化

分析了原有时间相关单光子计数光谱仪存在的不足,提出了改进方案。研制了高速数据采集系统,采用PCI总线技术、FPGA技术,开发了高速光谱数据采集卡,取代了原有的多道分析仪,数据采集速度达到20 MB/s,比原有仪器提高了约200倍;改善了仪器的性能、减小了体积。介绍了光谱仪系统的集成和工作流程,并对仪器的性能进行分析,通过多种标准样品的试验数据分析和对比,光谱仪系统具有最高的灵敏度-单光子计数,测得荧光寿命可达到ps量级,而且可以测得时间分辨光谱。     

利用圆锥辐射优化飞秒荧光光谱的光学参量放大

基于非共线光学参量放大的飞秒时间分辨荧光光谱技术是一种新的超快光谱研究方法.文章研究了荧光放大的参量过程.超连续的种子光其瞬时光强可以被线性放大.由于系统高达107的放大能力,泵浦脉冲能量的微小不稳定性在最终放大输出信号中将产生很大起伏.提出了一种利用圆锥辐射作为参考消除此干扰的方法.研究表明,探测的荧光动力学曲线有显著改善.