耗散旋波介质中的色散关系

应用Maxwell经典电磁理论，结合旋波介质的本构关系，研究耗散旋波介质中光波的色散关系．结果表明，色散关系与介质电导率、旋波因子等因素密切相关．     

电磁波在旋波介质中的传播特性研究

介绍了旋波介质的结构特征，讨论了旋波材料的电磁性质和物质方程，结合麦克斯韦方程和边界条件。给出了电磁波入射介质的反射系数和透射系数。，     

非旋波近似下级联型三能级原子与腔场相互作用的量子动力学性质

研究非旋波近似下级联型三能级原子与单模腔场的相互作用.结果表明：非旋波近似下，由于虚光场的影响，辐射场的平均光子数和二阶相干度的演化曲线均出现了“小锯齿状”，表现为系统的量子噪声，随着ω和的增大，量子噪声分别减小和增大；非旋波近似下，系统的反聚束效应较旋波近似的强；研究结果还揭示了平均光子数N(t)和二阶相干度g²(t)与原子-场耦合系数λ的关系. 关键词：     

广义Helmholtz方程的Green函数及旋波介质色散关系的另一求解方法

运用并矢法求解广义Helmholtz方程,结合Fourier变换、留数定理等数学处理,给出方程的并矢Green函数解析表达式;并进一步就旋波介质给出其中色散关系的另外一种求解方法．     

一种研究非旋波近似演化问题的系统近似方法

以一个与玻色场耦合的二能级粒子为例，证实了在静态极化子问题的研究中取得成功的相干态近似方法，同样也能够有效地用于非旋波近似下量子系统的时间演化问题。结果同时表明，在一般情况下，哈密顿算符中的非旋波项不能被忽略；并提供了在频率空间进一步检测非旋波项效应的可能性。     

非旋波近似下双光子Jaynes-Cummings模型中光子反聚束效应的研究

利用弱场-弱耦合-短时近似，研究了旋波近似与非旋波近似下双光子Jaynes－Cummings模型（JCM）中光子的反聚束效应，分析了虚光子过程对此效应的影响。     

旋波介质物质方程的等价性证明

在旋波介质研究过程中,人们提出了多种形式的物质方程.由于表达形式和使用符号的不同,很容易造成误解和混淆.本文对常用的4种物质方程形式进行了推导和整理,给出了它们之间的对应关系.     

薛定谔猫态光场与二能级原子相互作用系统的量子特性

在非旋波近似下,通过采用相干态正交化展开的方法,研究了薛定谔猫态光场与二能级原子相互作用系统中,原子的布局数和光场的反聚束效应,并与旋波近似下的结果进行了对比.在旋波近似与非旋波近似下,讨论了初始光场强度、相干态间的相位角以及失谐量对原子布局数和光场反聚束效应的影响;在非旋波近似下,讨论了强弱耦合情况下光场的反聚束效应.研究结果表明:旋波近似与非旋波近似下,原子的布局数随着初始光场强度的不同,表现出不同的特性;当初始光场强度较小时,旋波近似与非旋波近似下,原子的布局数表现出相同的特性;随着初始光场强度的增大,旋波近似下,原子的布局数将表现出坍塌现象.耦合强度较大时,光场的聚束与反聚束效应在非旋波近似与旋波近似下有较大的区别;非旋波近似下,随着初始光场强度的增大,光场一直处于聚束效应状态;而旋波近似下,光场的聚束效应与反聚束效应交替出现.     

非旋波耦合条件下微波控制的光学双稳与多稳

研究了在非旋波耦合条件下微波场建立的原子相干对光学双稳与多稳的控制.通过改变微波场的初始相位,可以有效地控制双稳与多稳的存在与否、迟滞环宽度和阈值强度的高低.旋波和非旋波耦合在物理上可视为双色激发,耦合的能级分裂成无穷多个子能级,原来的裸态跃迁变成无穷多个不同频率的跃迁.这些跃迁的相干叠加决定了介质的非线性吸收与色散,相干叠加的结果取决于微波场的相位. 关键词： 原子相干 非旋波耦合 光学双稳与多稳 相位控制     

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.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.