光子成像系统信号与噪声的统计特性分析

在去除光子图像的本底噪声时,根据微弱点目标的探测统计特性,以泊松分布均值与方差相等的特点为判据,提出了一种确定阈值选取范围的新方法。利用点过程的分析方法研究了光子受限点目标的探测统计特性,并进行了实验研究,结果表明光子受限点目标的探测统计特性服从平稳泊松点过程。利用以上分析方法可以快速地获得微弱点目标事件的期望发生率,以及在下一段时间内目标至少再出现一次的概率,从而为后续的目标探测、跟踪以及位置预测奠定了基础。     

Electroproduction of an electron-positron pair in a medium

The process of the electron-positron pair creation by a high-energy electron in a medium is analyzed. The spectral distribution over energies of created particles is calculated for the direct and cascade mechanisms of the process. The Coulomb corrections are included. The new formulation of the equivalent photon method is developed, which takes into account the influence of the multiple scattering. It is shown that the effects of multiple scattering can be quite effectively studied in the process under consideration. The text was submitted by the authors in English.     

光子计数成像研究

从APD阵列的响应特性出发,利用随机点的统计学描述,建立了光子计数成像的一维点过程数学模型。通过对光子事件发生时间统计特性的描述,分析了光子密度、门控时间、雪崩光电二极管恢复时间等因素对光子计数成像质量的影响。并采用蒙特卡罗方法,对近红外波段不同光子密度条件下多种计数间隔的成像质量进行了仿真,给出了仿真结果。     

Generation of light of second harmonic frequency in a Gaussian light

The process of second harmonic frequency generation in a chaotic (Gaussian) light on the basis of a simple quantum-mechanical model is studied in this work. It is shown that the process of second harmonic frequency generation in the chaotic light is quicker than that in the coherent light with the Poisson distribution of photon number.     

附加Kerr介质Λ型三能级原子与非关联双模相干态光场的压缩特性

采用旋波近似分析了附加克尔介质非关联双模相干态场与A型三能级原子相互作用系统的态矢量演化过程,叙述了两种光场压缩效应及应用,给出了光子数压缩和正交相位压缩计算公式,通过数值计算,绘出压缩光场随时间的演化过程并讨论了克尔介质对光场压缩特性的影响,结果表明强的克尔效应可以使光场的压缩随时间演化呈周期性变化,失谐较大时,光子数压缩品质差.     

Change of the photon statistics by one-photon absorption and by simultaneous one-photon and two-photon absorption

With the help of the generating function we investigate the change of photon statistics due to one-photon absorption. Photon distributions with antibunching approach by this process the Poisson distribution. In a second part we consider the simultaneous action of one-photon and two-photon absorption. We present the exact solution and the asymptotic state in the limit of great initial photon numbers.     

Evolution of the Photon-number Probability Distribution in the System of a Three Level Atom with an Added Kerr-like Medium

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Hamiltonian structure for Alfvén wave turbulence equations

A hamiltonian formulation using a noncanonical Poisson bracket is presented for a nonlinear fluid system that includes reduced magnetohydrodynamics and the Hasegawa-Mima equation as limiting cases. Nonlinear integral invariants for the system are found to be in the kernel of the noncanonical Poisson bracket. This Poisson bracket is given a Lie algebraic interpretation.     

On the hamiltonians for magneto-optical intensities

A multipolar semi-classical hamiltonian for magneto-optical intensities is derived by a canonical transformation taking Feynman's formulation of the conventional Pauli hamiltonian as the point of departure. Only interactions up to the order of electric quadrupole and magnetic dipole terms are retained. The resulting hamiltonians are divided into their respective time-independent, single photon and double photon parts, and the difference in the appearance of magnetic field dependent contributions in the perturbation terms is analysed. On the basis of this analysis it is argued that the magnetic field dependent term in the magnetic dipole transition moment operator may lead to a unique single photon process with an amplitude proportional to the static magnetic field. This process leads, amongst others, to transitions between totally symmetric atomic states, in contrast to the standard multipolar selection rules of ordinary spectroscopy.     

Independent photon deletions from quantized boson fields: The quantum analog of the Burgess variance theorem

It is demonstrated that if two boson fields are related by a process of independent random photon deletion, their moment-generating functions are related by an equation identical to that derived using classical arguments. A quantum analog of the Burgess variance theorem is recovered. The results confirm that the super- or sub-poissonian nature of a light beam is conserved, under the influence of independent Bernoulli deletions and/or additive independent Poisson noise. The identity results from the correspondence between classical and normally ordered correlation functions, for which vacuum fluctuations play no role.     

Photon polarization tensor in a magnetized plasma system

We investigate the photon polarization tensor at finite temperatures in the presence of a static and homogeneous external magnetic field. In our scheme, the summing of the Matsubara frequency is performed after Poisson resummation, which is easily completed and converges quickly. Moreover, the behaviors of finite Landau levels are presented explicitly. It shows a convergence while summing infinite Landau levels. Consequently, there is no necessity to truncate the Landau level in a numerical estimation. At zero temperature, the lowest Landau level (LLL) approximation is analytically satisfied for the vacuum photon polarization tensor. However, we examine that the LLL approximation is not enough for the thermal polarization tensor. The thermal tensor obtains non-trivial contributions from the finite-n Landau levels. And, photon spectra gains a large imaginary contribution in thermal medium, which is the so-called Landau damping. Finally, it is argued that the summation of Matsubara frequency is not commuted with Landau level ones, such conjecture is excluded in our calculations.     

The photon momentum

The momentum expression of a photon is derived by taking into account the absorption process by an electron. The defect of the actual momentum representation is shown by using the equations of energy and momentum conservation. The phase and group velocities of the photon that represents the particle aspect of light are also obtained with the aid of the new formulation.     

Sub- and super-Poissonian photon statistics of single-molecule fluorescence blinking

An analysis of intermittent fluorescence is presented for a single molecule driven by a continuous-wave laser field. The interruptions of fluorescence are caused by transition of the molecule to a triplet state. A method previously developed to calculate photon distribution for continuous-wave fluorescence is applied to analyze photon statistics of fluorescence blinking. The probability w _N (T) of counting N photons over a time interval T is derived for intermittent fluorescence. The photons counted over relatively short intervals are found to have a sub-Poissonian (narrower than Poisson) distribution. The photon distribution over intervals longer than the mean off time has a complicated form with two maxima; i.e., a super-Poissonian (wider than Poisson) distribution is obtained.     

Statistical analysis of recording light emitted by ZhS-19 glass

The statistical characteristics of light emitted by a radioluminescent source (ZhS-19 glass) and a light-emitting diode were obtained experimentally. The light recording in the photon counting mode was statistically analyzed. A conclusion was made that ZhS-19 glass is not a Poisson light source.     

Experimental demonstration of switching entangled photons based on the Rydberg blockade effect

The long-range interaction between Rydberg-excited atoms endows a medium with large optical nonlinearity. Here, we demonstrate an optical switch to operate on a single photon from an entangled photon pair under a Rydberg electromagnetically induced transparency configuration. With the presence of the Rydberg blockade effect, we switch on a gate field to make the atomic medium nontransparent thereby absorbing the single photon emitted from another atomic ensemble via the spontaneous fourwave mixing process. In contrast to the case without a gate field, more than 50% of the photons sent to the switch are blocked,and finally achieve an effective single-photon switch. There are on average 1-2 gate photons per effective blockade sphere in one gate pulse. This switching effect on a single entangled photon depends on the principal quantum number and the photon number of the gate field. Our experimental progress is significant in the quantum information process especially in controlling the interaction between Rydberg atoms and entangled photon pairs.     

Full-wave analysis of photonic-crystal structures with multi quantum well active region

In this paper, a semi-classical formulation for modeling photonic-crystal (PC) structures with a four-layer multi quantum well (MQW) active region is presented. The formulation treats the electromagnetic fields as a classical entity, while employing the quantum-mechanically derived rate equations to analyze the active medium. Using the Poynting theorem, we interrelate the two sets of equations, namely the MQW rate equations and Maxwell's equations. The formulation involves the stimulately emitted photon density in the former and a virtual volume current density representing the generated photons in the latter. With the help of this formulation, we then model a PC optical amplifier as well as a PC hexagonal-defect cavity laser and solve the obtained equations after replacing the involved spatial and temporal derivatives by pseudo-spectral and Runge-Kutta's formulations, respectively. The formulation also takes the effect related to gain saturation and frequency broadening into account.     

硅雪崩二极管光子辐射特性的实验研究

利用计数统计测量的方法，对工作在击穿状态下的硅雪崩光电二极管(APD)光子辐射的暂态特性以及计数统计特性进行了实验研究.将APD辐射光子的计数统计曲线与相应Poisson、热光场进行比较，发现其在采样时间为10 ms的情况下计数统计服从Super-Poisson分布.另外实验给出了APD光子辐射的光谱特性.     

Electroproduction of electron-positron pair in oriented crystal at high energy

The process of electroproduction of the electron-positron pair by high energy electron in an oriented single crystal is investigated. Two contributions are considered: the direct (one-step) process via the virtual intermediate photon and the cascade (two-step) process when the electron emits the real photon moving in the field of axis and afterwards the photon converts into the pair. The spectrum of created positron (electron) is found. It is shown that the probability of the process is strongly enhanced comparing with the corresponding amorphous medium.     

Field and intensity expectation values of quantum solitons in optical fibers

Expectation values of the field and intensity operators are evaluated for quantum solitons in the normalized fundamental soliton states with a Gaussian momentum superposition and a Poisson distribution for photon numbers. The associate quantum diffusion effects are discussed and the conditions which lead to the classical limit are identified. A numerical estimate is given using experimental data.     

Single photon self-interference via inelastic two-wave mixing in a coherently prepared cold medium

We investigate a coherently prepared cold medium for efficient single-photon inelastic two-wave mixing (ITWM), maximum Fock state entanglement and single photon self-interference. We show the possibility of generating maximally entangled single-photon state, and near 100% conversion efficiency for generating a frequency shifted TWM photon by proper choice of medium length and concentration. In addition, we demonstrate a new type of transparency effect produced by an efficient single photon self-interference, a transparency effect that is very different from the conventional electromagnetically induced transparency (EIT) process.