Evaluation of the Autocorrelation Function from Measurement of the Photocount Distribution

This paper establishes a clear relation between the photocount distribution (PCD) of a low light level signal and its autocorrelation function (AC). The conclusion is that the evaluation of the AC from the measurement of the PCD is equivalent to that of the AC. Although the signal to noise ratio decreases when AC evaluation is obtained from PCD measurements, this technique allows AC values to be obtained more quickly and easily. Theoretical evaluation of the variances involved in these measurements and a simulation checking procedure are also described.     

Non-Standard Normalization of the Second-Order Factorial Moment as a Method of Reducing the Error Involved in Characterizing Spectral Profiles

The use of non-standard normalized second-order factorial moment may reduce the error involved in analyzing a light signal.

In this work we derive the theoretical expression of the error obtained when this kind of functions is used. Experimental results for a periodic square wave-shape profile are given.     

Photocount statistics in mesoscopic optics

We report the first observation of the impact of mesoscopic fluctuations on the photocount statistics of coherent light scattered in a random medium. A Poisson photocount distribution of the incident light widens and gains additional asymmetry upon transmission through a suspension of small dielectric spheres. The effect is only appreciable when the average number n of photocounts becomes comparable or larger than the effective dimensionless conductance g of the sample.     

Determination of the Parameters Characterizing a Two Lines Spectrum by Measuring n(2)(T): Rectangular Profiles Approximation

In the present paper we study the possibility of analyzing a light beam with a spectrum of two lines, by measuring the normalized second order factorial moment of the photon-counting distribution of the light beam. Two lines with rectangular profile are considered in order to simplify calculations and experiments. The error in the determination of width, separation and relative height of lines is studied by means of an experimentally checked theoretical model.     

基于混沌和随机共振的微弱信号检测

推导了分数阶线性振子系统响应的一阶稳态矩的频率不变性和相移特性, 并通过理论分析得出, 在随机共振机制下, 分数阶线性振子对系统响应一阶稳态矩的幅值具有放大作用. 构造Duffing混沌振子检测器, 利用混沌系统对参数摄动的敏感性以及对噪声的免疫能力实现弱信号检测. 数值模拟证实, 该方法可以有效地从噪声背景中将微弱正弦信号检测出来, 并且相对传统的混沌检测方法能显著降低信噪比检测门限.     

Quantum mechanical photoncount formula derived by entangled state representation

By introducing the thermo entangled state representation,we derive four new photocount distribution formulas for a given light field density operator.It is shown that these new formulas,which are convenient to calculate the photocount,can be expressed as integrations over a Laguerre-Gaussian function with a characteristic function,Wigner function,Q-function and P-function,respectively.     

Two quantum-mechanical photocount formulas

We derive two quantum-mechanical photocount formulas when a light field's density operator rho is known; one involves rho's coherent state mean value and the other involves rho's Wigner function; when this information is known, then using these two formulas to calculate the photocount would be convenient. We employ the technique of integration within an antinormally ordered (or Weyl-ordered) product of operators in our derivation.     

Factorial moment of the photon counting distribution of gaussian-lorentzian light under various spatial coherence

The generating function of the photon counting distribution is studied under consideration of the spatial coherence. The high order factorial moments are induced from the generating function, and are found to be experimental proof for the theory. The behavior of the second factorial moment is investigated for the purpose of spectroscopy of Rayleigh scattered light. The factorial moment measurements are made by using a digitalized electric system. The spectral line shape is determined quantitatively under various spatial coherence conditions.     

电磁轨道发射中炮口电弧的抑制

采用一种导通时阻抗极低的外触发开关作为旁路器件, 在电枢即将出膛前开通此消弧器件, 使回路电流从器件流过, 从而达到抑制甚至消除炮口电弧的目的。对比试验表明, 在触发了消弧开关的试验中, 出膛时炮口电压显著降低, 轨道电流几乎全部流过消弧器件, 高速摄影亦显示电弧亮度明显降低, 消弧器件可有效抑制炮口电弧。通过比较触发信号与器件导通信号, 发现消弧器件的导通时刻较触发信号时刻有一定的延迟, 这在一定程度上影响了消弧器件抑制电弧的性能。     

Photocount statistics of gaussian light with analytic spectral profile

The letter derives an explicit expression for the generating function of the photocount distribution corresponding to gaussian light characterized by a triangle-shaped correlation function. The first six moments are compared with those derived from the approximate formula of Rice.     

Slow light via four-wave mixing in a hot rubidium vapour

In this work,we report on an off-resonant four-wave mixing experiment via a ladder-type configuration in a hot rubidium atomic vapour.We find for the first time,to the best of our knowledge,that the generated light is delayed compared with the reference.At the same time,the seeded signal beam is also delayed,though the delay time is not as so large as the one that the generated light has.Both delayed times can be adjusted experimentally by controlling the two-photon detuning.The experimental results are in good agreement with our theoretical predictions.Our results may be important for storing telecom-band photons.     

Approximate approach to the quantum statistics of the superposition of coherent and chaotic fields

Formulae recently derived for the integrated intensity distribution, the photon-counting distribution and its factorial moments in the statistics of the superposition of multimode coherent and chaotic fields are analyzed in greater detail and their validity as approximate formulae for light of arbitrary spectrum is investigated. It is shown by explicit calculation of the third factorial moment of the photon-counting distribution for the superposition of a one-mode coherent field with a Gaussian Lorentzian field that the proposed formulae hold with very good accuracy over a wide range of conditions.The authors thank Dr. Z. Braunerová and M T. Kojecký of the Computer Center of Palacký University for their help with calculations.     

Photon counting statistics of superposition of one-mode coherent light and chaotic light consisting of two Lorentzian spectral lines

The approximate photon counting distribution si calculated for the polarized superposition of one-mode coherent light and chaotic light consisting of two Lorentzian spectral lines. Further the exact and approximate third factorial moments of the photon counting distribution are proposed in this case. Also the second factorial moment for the superposition of one-mode coherent light and chaotic light consisting ofn Lorentzian spectral lines is given.The authors thank Dr. Z.Braunerová from Laboratory of Computer Science of Palacký University for performing the numerical calculations and Dr. V.Peinová for some verifying calculations.     

Photocount statistics of chaotic lasers

We derive the photocount statistics of the radiation emitted from a chaotic laser resonator in the regime of single-mode lasing. Random spatial variations of the resonator eigenfunctions lead to strong mode-to-mode fluctuations of the laser emission. The distribution of the mean photocount over an ensemble of modes changes qualitatively at the lasing transition, and displays up to three peaks above the lasing threshold.     

强流电子束加速器中气体开关的电磁辐射等效模型

对触发开关和主开关产生电磁辐射的机理进行了详细的分析,将气体开关导电通道等效为电偶极子,理论分析了其辐射电磁波的空间分布,以同轴电缆为实验对象,研究了电磁辐射的干扰。实验测量了触发开关和主开关的电磁辐射信号,结果表明, 运用偶极辐射等效可以很好地描述二者的辐射特性。在强流电子束加速器产生电磁辐射的时刻,同轴电缆中感应出了一定强度的电流,幅值达3 V,已经足以对其他信号的准确测量产生影响。     

高能碰撞实验数据非整数分割时的阶乘矩分析

在对相空间用非整数分割作阶乘矩分析时,由二粒子或多粒子关联所引起的非均匀因素的影响必须加以认真考虑.本文对高能碰撞末态粒子的阶乘矩在相空间进行非整数分割时的分析方法进行了仔细研究,建立了一套完整的对非整数分割下阶乘矩的分布进行修正的方法.用NA22实验组的实验数据计算,证明其方法是正确的.     

Manipulation of photon statistics of highly degenerate incoherent radiation

Highly degenerate incoherent radiation has a Gaussian density matrix and a large occupation number of modes f. If it is passed through a weakly transmitting barrier, its counting statistics is close to Poissonian. We show that a second identical barrier, in series with the first, drastically modifies the statistics. The variance of the photocount is increased above the mean by a factor f times a numerical coefficient. The photocount distribution reaches a limiting form with a Gaussian body and highly asymmetric tails. These are general consequences of the combination of weak transmission and multiple scattering.     

Direct observation of nonclassical photon statistics in parametric down-conversion

We employ a high quantum efficiency photon number counter to determine the photon number distribution of the output field from a parametric down-converter. The raw photocount data directly demonstrates that the source is nonclassical by 40 standard deviations, and correcting for the quantum efficiency yields a direct observation of oscillations in the photon number distribution.     

一种时间相关吸收光谱技术分析新方法

时间相关吸收光谱技术,如腔衰荡光谱技术(CRDS)和腔衰减相移光谱技术(CAPS),是近三十几年发展起来的一类新型吸收光谱检测技术,它具有探测灵敏度高、响应速度快、不受光源强度起伏变化影响等优点。传统的吸收光谱技术都是基于Lambert-Beer定律,如直接吸收光谱技术(DAS)、波长调制光谱技术(WMS)和腔增强吸收光谱技术(CEAS)等,这类光谱技术在探测物质微弱吸收的时候一旦遇到较强的背景光信号就变得难以测量,而且光源的不稳定性也会对检测带来一定的限制。时间相关吸收光谱技术由于其不受光源强度起伏变化的特点,在很大程度上能够弥补传统吸收光谱技术所存在的缺陷,但其也有自身的局限性。首先在理论上,CRDS和CAPS这两种时间相关吸收光谱技术并不统一,而且在现有光谱理论下,Pulse-CRDS在应用时使用的脉冲光源的脉宽必须远小于谐振腔本身的时间常数,对于长脉宽的脉冲光或者反射率低(小于99.9%)的腔体,现有理论将不再适用;CAPS在应用时光源调制信号必须是周期性的正弦信号或者方波信号,对于其他类型的周期调制信号或者非周期性信号,现有理论并没有涉及。针对上述提到的时间相关吸收光谱技术的局限性,提出了一种新的分析时间相关吸收光谱技术的方法,即利用一阶传递函数,将谐振腔视为一阶传感系统,对时间相关吸收光谱技术理论进行统一解释,在公式推导上证明新方法下的推导结果和现有理论结果的一致性。针对Pulse-CRDS,以高斯脉冲光为例,给出一阶传感理论下的透射光强表达式,并对一系列不同的脉冲宽度γ、谐振腔时间常数τ_real以及从输出信号中拟合而得的时间常数τ_anal进行了模拟仿真。经过分析比较后发现,当γ<0.3τ_real时,τ_anal和τ_real的偏差小于1%;当γ>0.3τ_real时,τ_anal和τ_real的偏差渐渐变大,将不再满足实验条件。为了使Pulse-CRDS在长脉宽脉冲光下也能应用,本文给出了修正函数,使得在脉宽大于腔衰荡时间0.3倍的情况下,经过修正补偿后,衰荡时间的误差小于1%。对于CAPS系统,搭建相应实验平台,LED中心波长选用405 nm,使用方波调制信号,测量不同频率下的入射参考信号与探测信号的相位差和探测信号峰-峰值,通过由一阶传递函数推导而得的相频特性和幅频特性,拟合得到时间常数τ,结果分别为7.24和7.25 μs,残差范围分别为[-0.01, 0.02]和[-0.02, 0.025],两者结果基本一致。实验结果验证了一阶传感系统理论完全适用于时间相关光谱的信号分析,并且一阶传感系统理论还使得时间相关光谱技术的理论得到了统一。     

Evolution of classical light statistics in coherent difference-frequency generation

Classical solution of coherent nonlinear difference-frequency generation process based on the averaging of stochastic quantities over the initial photocount distributions in pump and signal input radiations is presented in this paper. The evolution of second-order light statistics in difference-frequency generation with coherent and chaotic input radiations is calculated for arbitrary values of the time or space parameter.The author would like to thank Dr. M. Krková and Dr. J. Bajer from the Palacký University in Olomouc for performing the numerical calculations.