Compton散射对激光等离子体通道天线特性的影响

应用多光子非线性Compton散射模型和数值计算方法, 研究了激光等离子体通道天线传播和辐射特性,结果表明: 随通道周围介质损耗和传输模式阶数的增大, 传输模式TH n m衰减常数明显增大。这是因散射使通道内外电场和磁场增强, 粒子间碰撞频率增大, 电场使更多分子电离而吸收更多能量的缘故。随模式阶数增大, 电性有耗介质使相移常数明显减小。这是因散射使高阶模式可能存在被耦合电场俘获的缘故。等离子体耦合频率为0.7附近, 衰减常数随频率增大而剧烈增大。这是因散射使介质分子发生二、三阶电离, 更多电子被耦合电场急剧加速的缘故。随天线长度增加, 天线辐射方向图主瓣和副瓣数量、宽度和最大辐射方向发生明显变化, 这是因散射使天线频率增大, 辐射波长变短,粒子电离几率增大, 辐射波能量和频率成分增大的缘故。     

超强激光照射三维时变等离子体散射新机制

应用多光子非线性Compton散射模型和电流密度拉普拉斯变换改进的时域有限差分法,研究了超强激光照射三维时变等离子体的散射特性,提出了Compton散射光是影响等离子体散射的新机制,给出了该等离子体散射截面和频率随时间变化的修正方程,并进行了数值仿真。结果表明：与Compton散射前相比,Compton散射使等离子体散射截面增大,且随频率增大迅速衰减。这是因散射使等离子体中电子从耦合激光场中获得更多能量,从而导致电子被耦合场俘获的缘故;使瞬变等离子体最大频率随时间呈准直线缓慢下降趋势。这是因散射使等离子体中电子辐射阻尼效应增强,从而导致电子能量衰减、频率下降的缘故;使缓变等离子体频率随时间缓慢增大。这是因散射使等离子体中电子辐射阻尼增大效应减弱了频率增大的缘故。     

超强激光照射三维时变等离子体散射新机制

应用多光子非线性Compton散射模型和电流密度拉普拉斯变换改进的时域有限差分法,研究了超强激光照射三维时变等离子体的散射特性,提出了Compton散射光是影响等离子体散射的新机制,给出了该等离子体散射截面和频率随时间变化的修正方程,并进行了数值仿真。结果表明：与Compton散射前相比,Compton散射使等离子体散射截面增大,且随频率增大迅速衰减。这是因散射使等离子体中电子从耦合激光场中获得更多能量,从而导致电子被耦合场俘获的缘故;使瞬变等离子体最大频率随时间呈准直线缓慢下降趋势。这是因散射使等离子体中电子辐射阻尼效应增强,从而导致电子能量衰减、频率下降的缘故;使缓变等离子体频率随时间缓慢增大。这是因散射使等离子体中电子辐射阻尼增大效应减弱了频率增大的缘故。     

多光子非线性Compton散射对等离子体平面反射电磁波的影响

应用多光子非线性Compton散射模型和电磁波与等离子体相互作用模型,研究了Compton散射对等离子体平面反射电磁波特性的影响,提出了将Compton散射作为影响等离子体平面反射电磁波的机制,给出了等离子体平面反射电磁波反射率的修正方程,并进行了仿真实验.结果表明:不同频率下,低频段等离子体密度随电场强度增大而迅速增大,到达平衡态时间明显缩短,这是因散射使场强迅速增大,等离子体中粒子发生电离几率增大的缘故.高频入射波使反射波强度减低最多,最后几乎趋于0,这是因散射使等离子体频率高于入射波频率的成分大大增加的缘故.不同频率入射波的反射波频率有微小增大,这是因散射使信号与等离子体复合扩散时间尺度差距缩小,反射波的非线性效应逐步显现的缘故.随碰撞频率增大,低密度等离子体密度增加最快,到达平衡态时间最短,这是因散射使等离子体碰撞频率增大,有更多粒子参与电离的缘故.     

多光子非线性Compton散射对等离子体平面反射电磁波的影响

应用多光子非线性Compton散射模型和电磁波与等离子体相互作用模型,研究了Compton散射对等离子体平面反射电磁波特性的影响,提出了将Compton散射作为影响等离子体平面反射电磁波的机制,给出了等离子体平面反射电磁波反射率的修正方程,并进行了仿真实验。结果表明：不同频率下,低频段等离子体密度随电场强度增大而迅速增大,到达平衡态时间明显缩短,这是因散射使场强迅速增大,等离子体中粒子发生电离几率增大的缘故。高频入射波使反射波强度减低最多,最后几乎趋于0,这是因散射使等离子体频率高于入射波频率的成分大大增加的缘故。不同频率入射波的反射波频率有微小增大,这是因散射使信号与等离子体复合扩散时间尺度差距缩小,反射波的非线性效应逐步显现的缘故。随碰撞频率增大,低密度等离子体密度增加最快,到达平衡态时间最短,这是因散射使等离子体碰撞频率增大,有更多粒子参与电离的缘故。     

Compton散射对太赫兹波介质微腔光学特性影响

应用Compton散射模型、1维等离子体光子晶体模型和数值计算方法,研究太赫兹波段介质微腔光学特性,给出了系统反射率、反射相移和相位穿透深度修正方程和实验验证.结果表明:与散射前相比,分布式布拉格反射镜系统中心波长左移15μm,这是因散射使等离子体层中电子与光子碰撞频率增大效应导致系统振荡频率增大的缘故;反射相移在截止区与波长呈准线性关系,中心波长处相对π有一定偏离,这是因散射使等离子体层中电子辐射阻尼增强效应导致系统振荡频率减小的缘故;禁带区相位穿透深度增大,这是因散射与入射光形成的耦合光与入射光在禁带区的相位不同,导致入射光禁带对于耦合光产生局部失效的缘故.谐振峰左移15μm,强度提高了22倍,这是因散射产生的等离子体频率和电子辐射阻尼增大效应使系统中心波长左移,透射几率增大,从而导致透射禁带两个谐振峰左移和谐振峰强度提高的缘故.     

Compton散射下太赫兹波段介质微腔光学特性

应用Compton散射模型、1维等离子体光子晶体模型和数值计算方法,研究太赫兹波段介质微腔光学特性,给出了系统反射率、反射相移和相位穿透深度修正方程和实验验证。结果表明：与散射前相比,系统中心波长左移15 ,这是因散射使等离子体层中电子与光子碰撞频率增大效应导致系统振荡频率增大的缘故;反射相移在截止区与波长呈准线性关系,中心波长处相对 有一定偏离,这是因散射使等离子体层中电子辐射阻尼增强效应导致系统振荡频率减小的缘故;禁带区相位穿透深度增大,这是因散射与入射光形成的耦合光与入射光在禁带区的相位不同,导致入射光禁带对于耦合光产生局部失效的缘故。谐振峰左移15 ,强度提高了22倍,这是因散射产生的等离子体频率和电子辐射阻尼增大效应使系统中心波长左移,透射几率增大,从而导致透射禁带两个谐振峰左移和谐振峰强度提高的缘故。     

Compton散射下太赫兹波段介质微腔光学特性

应用Compton散射模型、1维等离子体光子晶体模型和数值计算方法，研究太赫兹波段介质微腔光学特性，给出了系统反射率、反射相移和相位穿透深度修正方程和实验验证。结果表明：与散射前相比，系统中心波长左移15 ，这是因散射使等离子体层中电子与光子碰撞频率增大效应导致系统振荡频率增大的缘故；反射相移在截止区与波长呈准线性关系，中心波长处相对 有一定偏离，这是因散射使等离子体层中电子辐射阻尼增强效应导致系统振荡频率减小的缘故；禁带区相位穿透深度增大，这是因散射与入射光形成的耦合光与入射光在禁带区的相位不同，导致入射光禁带对于耦合光产生局部失效的缘故。谐振峰左移15 ，强度提高了22倍，这是因散射产生的等离子体频率和电子辐射阻尼增大效应使系统中心波长左移，透射几率增大，从而导致透射禁带两个谐振峰左移和谐振峰强度提高的缘故。     

Compton散射对等离子体零色散附近调制不稳定性的影响

应用Compton散射模型和非线性Schrdinger方程,研究了Compton散射对等离子体零色散附近调制不稳定性的影响,提出了将Compton散射作为形成调制不稳定性的新机制,给出了等离子体修正色散方程,并进行了数值计算.结果表明:二阶色散较大时,远离零色散附近调制不稳定性增益谱由入射和散射光产生的二阶色散决定,随二阶色散增大,四阶色散作用迅速减小,这是因散射效应有效削弱了四阶效应的缘故.零色散附近调制不稳定性增益谱由入射和散射光产生的四阶色散决定,二阶色散被湮灭,微扰频率最大值向临界微扰频率较快靠近,这是因散射效应有效增强了四阶效应的缘故.增益谱宽随等离子体损耗增大而迅速增大,这是因功率增大使散射效应增强,导致带电粒子辐射阻尼增强的缘故.     

沿面闪络流体模型电离参数粒子模拟确定方法

介绍了粒子模拟确定高功率微波介质沿面闪络击穿流体模型相关电离参数的方法.对粒子模拟方法 (包括带电粒子动力学方程、次级电子发射以及蒙特卡罗碰撞模型)和流体整体模型方法 (包括连续性方程和能量守恒方程)做了简介.基于自编的1D3V粒子模拟-蒙特卡罗碰撞程序给出了在高(低)气压、不同气体种类以及不同微波场强和微波频率下流体模型电离参数的粒子模拟结果,包括电离频率、击穿时间、平均电子能量、电子能量分布函数类型.研究结果表明:平均电子能量与电子能量分布函数类型关系不大;中低气压下,电子能量接近Maxwell分布,电子能量分布函数类型对电离参数几乎没有影响;中高气压下,电子能量分布函数类型对电离参数有重要影响,其依赖系数X趋于高阶形式.不同气体的电子能量分布函数类型不同,需要利用粒子模拟对电子能量分布函数类型进行标定.同时,电子能量分布函数依赖系数与微波场强和频率也有关系,其随微波场强增加而增大,随微波频率增加而减小.在给定考察范围(微波场强在7 MV/m以下,微波频率在40 GHz以内),中低气压下,平均电子能量随微波场强增加而迅速增大,电离频率随微波场强增加先增大后降低,平均电子能量随微波频率增加而降低,电离频率随微波频率增加先增加后降低;高气压下,平均电子能量随微波场强增加而缓慢增大,电离频率随微波场强增加而增大,微波频率对平均电子能量和电离频率影响不大.     

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.