OCS分子在128nm附近的光解动力学研究:S(~3P_(J=2,1,0))、S(~1D_2)以及S(~1S_0)产物通道（英文）

本文利用时间切片离子成像技术对OCS分子进行了真空紫外波段的光解动力学研究.在四个光解光波长(从129.32到126.08 nm)下测量了硫原子解离产物S(~3P_J=2,1,0)、S(~1D_2)、S(_1S_0)的速度影像,并从中清晰地发现了四个主要的解离产物通道:S(~3P_(J=2,1,0))+CO(X~1∑~+),S(~3P_(J=2,1,0))+CO(A~3Π),S(~1D_2)+CO(X~1∑~+)和S(~1S_0)+CO(X~1∑~+).在实验影像中,产物CO分子的部分振动态结构能够得到分辨.实验还获取解离产物总平动能谱,产物分支比和角分布.对实验结果进行分析显示除绝热解离通道S(~3P_(J=2,1,0))+CO(A~3Π)之外,在共他三个产物通道中非绝热效应都起到非常重要的作用.     

CS2分子^1B2（^1∑u^＋）态预解离动力学研究

研究了CS2分子^1B2(^1∑u^+)预离解态线形势垒下的g振动能级光解动力学，包括预解离寿命、产物振转布居、平动-振动-转动能量分配和解离通道分支比．在实验过程中，一束可调谐激光激发超声射流冷却的CS2分子到^1B2(^1∑u^+)电子态，光解产物CS用另一束可调谐激光通过激光诱导荧光(LIF)方法检测．通过拟合光解碎片激发谱的谱峰轮廓，获得了源于不同跃迁初始态的^1B2(^1∑u^+)态g振动能级的预解离寿命．通过分析CS的LIF光谱，则获得了不同光解波长下CS碎片的v=0—8振动态布居、v=1、4—8振动态的转动布居、能量分配以及两个预解离通道CS(X^1∑^+)+S(^3PJ)和CS(X^1∑^+)+S(^1D2)的分支比．实验还考察了初始态弯曲振动量子数v2″、振动角动量量子数l对解离动力学的影响．发现v2″的影响不大，而l的影响却是明显的．较大的l(=K)对应于较短的寿命和较小的通道分支比S(^3PJ)／S(^1D2)，即大的l(=K)有利于预解离的发生，同时更有利于产生S(^1D2)．     

CS2 分子 1 B2(1 Σ+u )态预解离动力学研究

研究了CS2 分子1B2 (1Σ+u )预离解态线形势垒下的g振动能级光解动力学,包括预解离寿命、产物振转布居、平动振动转动能量分配和解离通道分支比.在实验过程中,一束可调谐激光激发超声射流冷却的CS2 分子到1B2 (1Σ+u )电子态,光解产物CS用另一束可调谐激光通过激光诱导荧光(LIF)方法检测.通过拟合光解碎片激发谱的谱峰轮廓,获得了源于不同跃迁初始态的1B2 (1Σ+u )态g振动能级的预解离寿命.通过分析CS的LIF光谱,则获得了不同光解波长下CS碎片的v=0~8振动态布居、v=1、4 ~8振动态的转动布居、能量分配以及两个预解离通道CS(X1Σ+ ) +S(3PJ)和CS(X1Σ+ ) +S(1D2 )的分支比.实验还考察了初始态弯曲振动量子数v2″、振动角动量量子数l对解离动力学的影响.发现v2″的影响不大,而l的影响却是明显的.较大的l(=K)对应于较短的寿命和较小的通道分支比S(3PJ) /S(1D2 ),即大的l(=K)有利于预解离的发生,同时更有利于产生S(1D2 ).     

HNCO在201 nm的离子成像光解动力学:CO(X~1Σ~+)与NH(a~1△)态相关性（英文）

本文通过时间切片离子速度成像技术在201 nm附近研究了HNCO分子在S_1电子激发态的光解动力学.CO产物通过共振增强多光子电离的方法进行了选态探测,获得了CO产物的振动基态和激发态切片影像.从CO的影像得到了解离产物的能量分布和空间角分布,确定了NH(a~1△)产物的振转态分布信息.研究发现~1NH的振动分支比(v=1/v=0)随CO(v=0)转动能的增大先增大后下降,展现了~1NH与CO之间特殊的态态相关性.大约一半的可资用能分配给解离产物的平动自由度.负的各向异性参数表明HNCO的光解是个快速的直接解离过程.     

Raman紫外双共振研究C_2H_2分子的碰撞转动弛豫

本文利用受激Raman抽运,选择性地制备了C_2H_2分子电子基态的红外非激活振动能级的单一转动态(X~1∑~+,v″=1,J″=9,11,13),并从紫外激光诱导的A~1Au(v′=1)←X~1∑~+(v″=1)荧光谱,直接测定上述三个转动态的C_2H_2—C_2H_2碰撞的消激活速率常数,它们分别为(7.96±1.04)×10~(-10),(8.79±0.97)×10~(-10),(8.76±0.88)×10~(-10)cm~3~(-1),以及由这些初始转动态向其它不同转动态(v′=1,J′=1,3,5,7,9,11,13,15)多量子跃迁转移的激活速率常数。     

Rb与H_2的反应碰撞:Rb(6~2D)+H_2→RbH+H

在样品池条件下,应用脉冲激光的泵浦-检测技术,研究了Rb(6~2D)激发态原子与H_2反应碰撞生成的RbH分子的振转能级的布居数密度分布及平均转动能、振动能、平动能的相对比值.发现RbH(X~1∑~+)只有v=0,1上有布居.转动带分布轮廓与池温下的统计分布接近,得到RbH的Boltzmann转动温度稍低于池温,而振动温度高.v=1和v=0上的布居数之比约为0.69,从而得到RbH(X~1∑~+)上平均转动能和平均振动能,由反应的有效能得到平均平动能,这三种能量的相对比值f_R:f_V:     

CdH分子基态X~2∑~+和激发态A~2П光谱和寿命测量

采用一束激光为泵浦光另一束激光为探测光的方法,获得CdH分子A~2Π态和X~2∑~+态之间跃迁产生的具有转动结构的多个荧光谱和激发谱带.对荧光的时间分辨研究,给出A~2Π态寿命τ_0=59.5±2.3ns,对A~2Π(v=0)态Cd原子的碰撞猝灭截面为(1.31±0.03)×10~(-15)cm~2;X~2∑~+态寿命τ_0=61.0±4.6μs,引起X~2∑~+(v=0)态寿命衰减的碰撞截面为(1.1±0.1)×10~(-18)cm~2.     

离子速度成像法研究HNCO分子在210 nm的光解动力学

用三维离子速度成像方法研究了HNCO分子在210 nm光解下的光解动力学．得到了光解产物CO在不同转动态的角分布和平动能分布．结果表明，HNCO分子在210 nm光解的主要通道是产生NH(a1￠)+CO(X1§+)的通道；碎片CO具有很高的转动激发，而NH的转动激发很小，约50％可资用能转化为平动能，该通道解离能确定为42738 cm?1；解离各向异性参数ˉ 最小为?0.75，且随着NH转动激发增大．该研究首次实验上证实了HNCO分子的快速、直接解离过程．ˉ值随NH的转动变化可以用经典碰撞模型予以解释．     

OCS分子在207 nm的光解动力学研究:S(~1D_2)+CO(X~1∑~+)产物通道（英文）

利用直流时间切片离子成像技术对OCS分子在紫外波段207nm的光解产物S(~1D_2)进行了偏振实验研究.通过在两种不同的共振增强多光子电离中间态,~1F_3和~1P_1,以及四种不同的泵浦-探测激光偏振几何构型下探测了光碎片S(~1D_2)的角动量极化特性.使用分子坐标系极化模型和实验室坐标系各向异性模型提取和分析出对应产物CO(X~1∑~+)的角分布.观测到的总平动能释放谱表明解离过程存在三种解离通道,分别对应于低、中、高平动能解离通道.低、中平动能通道的来源与光解波长在较长波长下得到的双峰分布来源一致.高平动能通道是一种新的解离通道,它来自于单重排斥态A(2~1A')的直接解离.     

基于3~3Σ_1~+共振耦合态制备超冷基态~(85)Rb~(133)Cs分子的实验研究

本文3~3Σ_1~+以为中间激发态,通过扫描光缔合光的频率得到了3~3Σ_1~+的不同振动态光谱。研究发现利用短程光缔合制备的超冷基态~(85)Rb~(133)Cs分子产率在3~3Σ_1~+(v=3)处较其他振动态更大,3~3Σ_1~+(v=3)转动常数较邻近的振动态有明显变化且与2~3Π_(0-)(v=14)的能量接近,这些特征显示了这两个振动态的共振耦合特性。优化光缔合光的功率和光电离光的能量后,我们得到X~1Σ~+(v=0)最低振动态超冷~(85)Rb~(133)Cs分子的产率为1.5×10~4/s。在考虑了分子波函数的宇称和跃迁选择定则后,我们发现3~3Σ_1~+(v=3,J=1)存在单步自发辐射制备超冷基态~(85)Rb~(133)Cs分子的通道,采用该通道可实现原子-分子相干转移直接制备超冷基态分子。     

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.     

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.     

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.