氢负离子在梯度电场中光剥离的波包动力学研究

利用含时微扰论和闭合轨道理论相结合的方法, 给出了氢负离子在梯度电场中自关联函数的计算公式, 并且对体系的自关联函数进行了计算和分析. 重点探讨了激光脉冲的宽度、梯度电场中背景电场强度及电场梯度对氢负离子体系的自关联函数的影响. 研究结果表明, 当激光脉冲的脉冲宽度较短, 远小于剥离电子的闭合轨道的周期时, 量子波包的回归现象显著, 自关联函数中会出现一系列比较明显的回归峰, 这是由于沿闭合轨道返回的电子波包和出射的电子波包之间产生干涉形成的. 但是随着激光脉冲宽度的增加, 量子波包的回归现象减弱. 当脉冲宽度和闭合轨道的周期相差不是很大时, 自关联函数中的回归峰逐渐变宽, 振荡渐趋平缓, 相邻的峰之间发生相互干涉, 从而导致对应关系消失. 除此之外, 我们还发现梯度电场中背景电场强度和电场梯度对体系的自关联函数也会发生显著的影响. 随着背景电场强度和电场梯度的增加, 剥离电子的闭合轨道的周期变短, 自关联函数中回归峰的个数逐渐增加, 量子回归现象增强. 因此, 我们可以通过改变脉冲的宽度、外加电场强度的大小对氢负离子发生光剥离的自关联函数进行调控. 我们的结果对于实验研究原子或离子体系在外场中的波包动力学性质可以提供一定的参考价值.     

液面微幅波动的激光干涉测量

对于低频微幅的液面波动,提出了一种激光干涉测量方法.实验上观察到了清晰、稳定的激光干涉图样.干涉图样受到调制,光强在两边界位置达到极大,形成两个极亮条纹.干涉条纹被限制在两个极亮条纹之间的确定区域内.根据光干涉理论推导出了调制干涉条纹光强度、相邻条纹角宽度、干涉区域角宽度与液面波物理参量之间的解析关系,该理论分析与实验...     

激光场和温度对氢氰酸分子准直的影响

通过分裂算符方法求解氢氰酸(HCN)分子的核转动波包,研究了激光场脉冲宽度、载波频率、激光峰值强度以及转动温度等参数对HCN分子准直程度的影响.结果表明,在温度T=10 K,使用脉冲宽度为100 fs,波长为800 nm,激光峰值强度I4×10~(13)W/cm~2范围内的激光场准直HCN分子时,最高准直度随光强增加升高,并且随光强增加,最高准直度增速变缓.在温度T=10 K,准直激光脉冲宽度为100 fs,波长为800 nm,峰值强度I=2×10~(13)W/cm2时,随激光载波频率在0.38×10~(15)Hzv1.13×10~(15)Hz范围内增加,HCN分子最高准直度出现振荡,在载波频率v=(0.4+0.1·n)×10~(15)Hz(n=1,2,3)时,最高准直度取极大值.在准直激光脉冲宽度为100 fs,波长为800 nm,峰值强度I=2×10~(13)W/cm2时,随温度在0 KT90 K范围内上升,准直度明显下降.     

法布里-珀罗干涉在超短激光脉冲测量中的应用

把大学物理光学中法布里-珀罗干涉的方法应用于超短激光脉冲测量.分析了利用法布里-珀罗标准具中多光束干涉产生自相关信号进行超短激光脉冲测量的原理;进行了实验测试并与迈克耳孙干涉自相关的测量结果进行了对比,实现了对超短激光脉冲时间宽度的测量.     

分光棱镜干涉法测量涡旋光束拓扑荷

理论分析并实验研究了涡旋光束通过单分光棱镜后的自干涉现象.研究结果表明,不同于涡旋光束与平面波或者球面波干涉,涡旋光束自干涉条纹呈"扭曲"状,且在干涉条纹边缘处会出现"断裂"条纹,其数目随着涡旋拓扑荷数增大而增大,且"断裂"条纹的指向与拓扑荷符号相关.上述结论提供了一种原理和操作简单的测量涡旋光束拓扑荷数的方法.     

基于多光束干涉的长程轮廓仪

为提高长程轮廓仪(LTP)面型检测的精度,提出一种使用波面型等光程多光束分束器的LTP。该分束结构可将入射光束分成若干束等光强等光程的相干光。在理论上分析计算了傅里叶变换(FT)透镜焦平面上干涉条纹的位置和强度分布,探究了零级干涉主极大条纹宽度、振幅和±1级干涉主极大条纹振幅与多光束分束器各结构参数之间的关系。通过选取合适的参数设计了基于多光束干涉原理的新型分束器,并与传统分束器进行了仿真实验比较,设计了测量系统中的准直镜和FT透镜,在Zemax软件中建立了完整的光学系统模型,并对该模型进行了实验验证。结果表明多光束干涉长程轮廓仪可以实现对被测表面斜率的测量,其在探测面上的干涉条纹宽度比传统双光束干涉窄,光强也更加集中,可以提高LTP的测量精度。     

一种新的Fabry-Perot干涉条纹处理方法

介绍了一种提取Fabry-Perot(法布里-帕罗)干涉条纹圆心点坐标和条纹半径的新方法。首先对干涉图像依次进行二值化处理,对所得到的条纹强度曲线进行均平滤波和自适应滤波,根据条纹灰度值强度余弦函数分布的特点,对条纹灰度值数据进行最小二乘法拟合,获得条纹强度峰值坐标,通过精确的迭代算法,进而获得Fabry-Perot干涉条纹圆心点的坐标;然后再对干涉条纹进行圆周积分,从而可以确定每级Fabry-Perot干涉条纹的半径长度。该方法可提高计算精度,减小计算误差。     

低频声表面波对细激光束的衍射效应

对于频率为几十赫兹的液体表面声波,实验上观察到反射光所形成的稳定、清晰的激光干涉图样.改变表面声波振幅,进一步发现了干涉图样的调制效应.调制效应明显地表现为干涉条纹的缺级,并且随表面声波振幅变化.依据波动光学原理,分析了调制作用下光束干涉所产生的光强解析分布及条纹特征,得到了干涉条纹角宽度与表面声波之间的解析关系,并据此对表面声波的特性参量波长和振幅及各级条纹相对光强分布规律进行了测定.     

基于迈克耳孙干涉仪的自相关仪

根据大学物理光学中迈克耳孙干涉仪的基本原理,设计实现了基于迈克耳孙干涉仪的自相关仪.分析了利用自相关仪的干涉自相关进行超短激光脉冲测量的原理;进行了实验测试,实现了对超短激光脉冲时间宽度的测量.     

干涉法测量低频表面波的衰减系数

对于频率为几十赫兹的低频衰减液体表面波,结合激光干涉法和激光扫描法,实验得到反衬度很高的调制干涉图样,理论上给出了干涉图样的条纹宽度,条纹分布范围与表面声波振幅之间的解析关系,实时测量了液体表面波的衰减系数.     

Influence of laser pulse on the autocorrelation function of H in a strong electric field

The autocorrelation function of electronic wave packet of hydrogen atom in a strong electric field below the zero-field ionization threshold is investigated in the formalism of semiclassical theory. It is found that the autocorrelation depends on the applied laser pulse significantly. In the case of narrow laser pulse, the reviving peaks in the autocorrelation can be attributed to the closed orbits of electrons, which are related to the classical dynamics of the system. But this correspondence is wiped out with increasing the laser width because of the interference among the adjacent reviving peaks.     

Femtosecond first-order autocorrelation measurement based one-photon induced photocurrent in Si Schottky diodes

Si Schottky diodes promise to provide cheap, reliable, and linear detectors for use in femtosecond and picosecond pulse width measurement. At low pulse excitation density (<100 pJ/cm²), the pulse width can be deduced from the first-order autocorrelation, and the measured results are in agreement with the theoretical ones. When pulse excitation density is larger than 1 nJ/cm², the pulse trailing edge is distorted due to bandgap reduction in semiconductor Si and the pulse width cannot be measured accurately by means of the first-order autocorrelation. The interference fringes presented in the first-order autocorrelation measurement can provide a way of calibrating the delay, and the pulse width can also be obtained by calculating the number of interference fringes.     

Time-resolved photodetached spectroscopy of H in electric field near an elastic surface

The advances in femtosecond laser techniques facilitate the investigation of ultrafast electron dynamics on surfaces directly in time domain. The time-resolved spectroscopy of negative hydrogen ion in electric field near an elastic surface is investigated in the framework of semiclassical theory. We analyze the autocorrelation function and its dependence on the laser pulse width and external field strength. When the applied pulse width is very narrow, the reviving peaks in the time-resolved spectrum can be attributed to the closed orbits of electrons. With the increase of pulse width, the adjacent peaks interference mutually and finally merge. Furthermore, the number and amplitude of peaks in the time-resolved spectrum increases obviously with the increasing field strength.     

激光在湍流大气中的干涉仿真

通过研究激光在湍流大气中的传输情况，旨在为光学高分辨率干涉成像提供理论依据。采用相位屏的近似处理方法对激光通过大气湍流传输进行模拟，研究激光通过湍流大气的干涉情况。试验结果表明：孔径间距越大，干涉条纹越密；在传输距离为2km，大气湍流折射率结构常数C2n为10-14，即接近强湍流的情况下，可以形成比较好的干涉条纹。孔径间距较小时，干涉的明暗条纹清晰可见。在实际干涉成像中，可以选择适当的孔径间距来获得较好的干涉条纹，从而获得目标的高分辨率像。     

超二代微光像增强器Na2KSb(Cs)多碱光电阴极荧光谱研究

利用785 nm波长激光作为激发源,测量了超二代微光像增强器Na2KSb(Cs)多碱光电阴极的荧光谱.试验中发现该荧光谱不是一条光滑的高斯型曲线,而是一条在高斯型荧光谱上叠加了一定频率间隔小锯齿峰的曲线.经实验验证和理论分析证明该荧光谱上的小锯齿峰是一种干涉条纹,与超二代微光像增强器的结构有关.干涉条纹之间的间距与相邻两干涉峰波长的乘积成正比,与超二代微光像增强器的近贴聚焦距离成反比.干涉条纹调制度大小与Na2KSb(Cs)多碱光电阴极的厚度成反比.通过测量超二代微光像增强器Na2KSb(Cs)多碱光电阴极荧光谱上两相邻干涉条纹的间距和调制度,就可以测量或比较出不同超二代微光像增强器Na2KSb(Cs)多碱光电阴极的膜厚、近贴聚焦距离.研究结果对提高超二代微光像增强器阴极灵敏度和分辨力提供了一个有效的分析手段.     

Interferometric autocorrelation of an attosecond pulse train in the single-cycle regime

We report on the direct observation of the phase locking of the attosecond pulse train (APT) via interferometric autocorrelation in the extreme ultraviolet region. APT is formed with Fourier synthesis of high-order harmonic fields of a femtosecond laser pulse. Time-of-flight mass spectra of N+, resulting from the Coulomb explosion of N2 absorbing two photons of APT, efficiently yield correlated signals of APT. The measured autocorrelation trace exhibits that the duration of the pulse should be only 1.3 periods of the extreme ultraviolet carrier frequency. A few interference fringes within the short pulse duration clearly show two types of symmetry, which ensure the phase locking between pulses in APT.     

Ultra-compact TDLAS humidity measurement cell with advanced signal processing

In this paper, tunable diode laser absorption spectroscopy humidity measurements with an ultra-compact measurement cell are presented. The optical path length is 2 cm. The system uses a vertical cavity surface emitting laser at 1.854 μm. The main limiting factor of the humidity resolution is not the noise but interference fringes produced by reflecting surfaces. Next to the system setup, a novel rejection method to eliminate these fringes, based on Fourier domain analysis of the absorption line, is described. In contrast to other fringe rejection methods, the presented method is able to handle fringes, whose free spectral range is in the range of the half width of the absorption line. The achievable humidity resolution for the presented cell is below 0.25 % relative humidity at room temperature.     

Some effects of optical alignment errors in a differential laser Doppler velocimeter

A formulation has been developed to treat the effects of alignment errors of the optical system used in a differential laser Doppler velocimeter. It is then applied to analyse the properties of output beat signals obtained by the velocimeter. The effects of optical alignment errors on the spectral width and signal-to-noise ratio of the output beat signals and on the probing volume are investigated in some detail. The spectral width is not affected very much by the deviation of the angle between two beams incident on the probing volume, but depends mainly on the number of interference fringes produced in that volume. The signal-to-noise ratio is very sensitive to the displacement of two incident beams on the probing volume and is also affected by the intensity and beam width differences of these two beams. The probing volume is evaluated in the case of two incident beams having different beam widths.     

A novel technique for measurement of self-generated magnetic fields and the plasma density in laser produced plasmas from the Faraday rotation using two color probes

Diagnostic information about the self-generated magnetic fields (SGMF) generated in laser produced plasmas is normally obtained by measuring the Faraday rotation angle (FRA) of a linearly polarized laser probe beam passing through the plasma. Simultaneous recording of the corresponding interferogram is required to get the density information necessary for estimating the magnetic field. The problem with this method is that the visibility of the fringes in the interferogram can be poor, and the SGMF cannot be calculated in the regions where the interference fringes are not observable. In this paper, we propose a new method to obtain the density distribution and the SGMF from two simultaneous measurements of FRA using two probe beams of different colors, which allows one to calculate the SGMF without the need of interferometry.