用零相关相位板匀滑散斑的理论研究

对零相关相位板匀滑散斑的特性进行了理论分析和散值计算,结果表明尽管零相关相位板是针对入射场为平面波面而设计的,但在入射场的振幅和相位有一定起伏的情况下,其远场光斑的散斑对比度明显低于采用随机相位板的情形.因而用零盯关相位板匀滑散斑是一种更为有效的方法.     

随机位相板对激光束的变换特性

用衍射积分理论在较为一般的情况下,对激光束通过随机位相板后的准远场特性进行了理论分析和数值模拟研究.主要分析了随机位相板的光斑匀滑、光斑包络控制以及斑纹抑制等重要特性,得到了一些新的结果,对随机位相板的应用有参考意义. 关键词：     

基于随机输入的束匀滑位相板研究

根据随机畸变激光波前入射确定束匀滑位相板的模型,利用随机理论分析了光束通过位相屏后的传输特性、透射光远场分布的统计均值和方差.通过计算得知远场分布的方差与位相屏的傅里叶谱的平方成正比.利用数值模拟计算了随机生成的两个波前分别通过两个位相屏后的远场分布,模拟结果证实了位相屏用于随机相位畸变激光束匀滑的可行性,并显示了匀滑效果.     

基于随机输入的束匀滑位相板研究

根据随机畸变激光波前入射确定束匀滑位相板的模型,利用随机理论分析了光束通过位相屏后的传输特性、透射光远场分布的统计均值和方差.通过计算得知远场分布的方差与位相屏的傅里叶谱的平方成正比.利用数值模拟计算了随机生成的两个波前分别通过两个位相屏后的远场分布,模拟结果证实了位相屏用于随机相位畸变激光束匀滑的可行性,并显示了匀滑效果.     

连续位相板均方根梯度对焦斑匀滑特性的影响

为满足惯性约束聚变(ICF)系统中,对焦斑均匀辐照的条件,研究了连续位相板(CPP)面形特征对远场光斑质量的影响.从波动光学和几何光学两个不同的角度建立分析模型,并利用均方根梯度这一参数将其统一起来.利用所建立的分析模型,通过数值计算研究了CPP面形均方根梯度对低频畸变光束的匀滑效果.结果表明:随着CPP均方根梯度增大,匀滑后的远场焦斑半径增大;光束顶部不均匀性先很快减小,再缓慢降低,最后趋于不变,可见CPP对光束的匀滑效果明显;束匀滑过程对能量利用率的影响先几乎不变,然后逐渐减小.当CPP的相关长度不变,均方根梯度在0.2-0.8 wave/mm范围内时,光斑尺寸、光束顶部不均匀性及能量利用率都在较好的范围. 关键词： 连续位相板 均方根梯度 光束匀滑 聚焦光斑     

基于光克尔效应的径向光束匀滑新方案

针对惯性约束聚变装置中提高靶面辐照均匀性的要求, 提出了一种基于光克尔效应的径向光束匀滑方案, 其基本原理是利用光克尔介质和周期性高斯脉冲光束相互作用实现对激光束透射波前附加周期性的球面位相调制, 以周期性地改变激光束远场焦斑尺寸, 进而引起远场焦斑内部散斑的快速径向扫动, 从而在积分时间内抹平靶面焦斑的强度调制, 实现径向方向的光束匀滑. 通过建立基于光克尔效应的径向光束匀滑的理论模型, 分析了焦斑形态及其径向匀滑特性, 并讨论了光克尔介质的选取和径向扫动特性. 结果表明, 基于光克尔效应的径向光束匀滑方案可以有效地实现远场焦斑内部散斑的周期性径向扫动, 从而在积分时间内快速改善靶面辐照均匀性.     

散斑场的随机波数及其参量非线性效应

散斑光场在非线性领域有特别的作用,它可用于抑制强光条件下的非线性过程.为了深入了解散斑的参量非线性作用机制,引入了具有波数失配的耦合波方程,讨论了方程的解,波数或位相匹配条件,波数不完全匹配时的增益阈值条件,以及完整解的待定系数.待定系数由边界场决定,如果边界的三个非线性波的复振幅都不为零,还存在边界位相匹配条件,满足该条件的待定系数最大.散斑光场的波数随机起伏,需要分段处理,这种波数随机起伏还会破坏边界位相匹配条件,从而抑制非线性增益.理论研究和数值计算的结果一致表明了散斑对受激布里渊散射参量过程的抑制作用.     

基于光克尔效应的径向匀滑方案参数优化

在基于光克尔效应的径向匀滑方案中,抽运光脉冲序列利用非线性介质的光克尔效应对激光束附加周期性的球面位相调制,从而使激光束远场焦斑内部散斑产生周期性的径向扫动,以改善远场焦斑均匀性。为了分析抽运光时间特性的改变对匀滑效果的影响,建立了径向匀滑方案的理论模型,并利用该模型对抽运光的时间特性参数进行了分析及优化。结果表明,在抽运光子脉冲之间的延迟时间一定时,子脉冲的脉宽过大或过小均会降低激光束远场的辐照均匀性,而随着子脉冲脉宽的增大,激光束远场的辐照均匀性随积分时间的波动相对趋于稳定,因而在避免产生明显"拍频"现象的前提下,选取较大的抽运光子脉冲脉宽更有利于实现稳定的匀滑效果。激光束与抽运光的时间同步精度对初期的匀滑效果有较大的影响,当抽运光提前1/5个周期左右时,可以在更短的积分时间内达到较好的径向匀滑效果。此外,不同的抽运光时间波形所获得的匀滑效果也有所不同,当抽运光的时间波形为三角波时,焦斑内部散斑的径向扫动速度较为稳定,可以使径向匀滑的整体效果及稳定性得到有效改善。     

高斯相关随机表面光散射散斑场相位奇异及其特性的理论研究

通过对二维高斯相关随机表面在远场平面上产生的散斑场及其相位的计算模拟, 发现在某一平面上除了实部零值线与虚部零值线有传统相交之外, 还有相切和重合的情况.切点和重合线也可以形成相位奇异, 并且其周围相位分布与传统的实部零值线与虚部零值线相交形成的奇点周围相位的螺旋变化不同, 呈现出对称性和不连续性的特征. 随着光波的传播, 在不同的观察面上散斑场复振幅的实部零值线和虚部零值线的相对位置经历了由相切到重合再到相交的演变过程, 相位奇异现象也随之发生变化. 关键词： 相位奇异 相位跃变 散斑场     

散斑场相位涡旋及其传播特性的实验研究

用CCD记录散斑场和参考光的干涉图样, 利用傅里叶变换法实现了散斑场复振幅以及相位分布的实验提取, 在复振幅实部零值线和虚部零值线切点处出现一种新的相位奇点, 与两条零值线交点处的传统相位奇点周围单调螺旋变化的相位分布不同, 绕切点一周的相位具有先增大后减小几乎呈对称性分布的特性, 为了解释这种新的相位奇点,提出了准孪生相位涡旋的概念. 在理论研究散斑场强度的纵向自相关函数的基础上, 实验观察散斑场相位涡旋的传播, 发现在光强纵向相关长度范围内的不同传播距离处的观察面上, 复振幅实部和虚部随机变化而涡旋的 关键词： 相位涡旋 散斑 干涉     

Fast microstructuring of silica glasses surface by NIR laser radiation

The glass surface microstructuring technology using laser radiation with NIR wavelength (λ=1.064 μm) was revealed in this work. Glass plates were placed on the cellular graphite surface. Focused laser radiation passed through the glass plate and interacted with cellular graphite. The radiation heated the graphite surface and thus the high temperature influenced the back side of the glass plate. After consecutive laser scans, having certain periods and interruptions of laser radiation, the microstructures with depth ~0.5 μm were formed. Besides, in this work we suggested the method to calculate optical characteristics of formed elements. It was experimentally shown that these microstructures could be used to form phase diffraction gratings (PDGs) and random phase plates (RPPs). We experimentally demonstrated the possibility of these elements being used as RPPs which are suitable for multimode laser radiation homogenization and as PDGs which are suitable for laser simultaneous processing of metal films.     

固定边矩形板的弯曲问题

The problem of bending of orthotropic rectangular plates with clamped edges on elastic foundation may be reduced to the following differential equation and boundary conditions (?⁴w)/(?x⁴)+2λ(?⁴w)/(?x²?y²)+(?⁴w)/(?y⁴)+kw=q/D. w=0, (?w)/(?x)=0 at x=±a, w=0, (?w)/(?y)=0, at y=±b. In the case of isotropic plates, λ = 1. In this paper a perturbation method is proposed for the solution of this problem fay expanding w in power series of λ: w=w₀+w₁λ+w₂λ²+……. It is proved that this series is convergent when -1 ≤λ≤1.     

Investigation on high power phase compensation of strong aberrations via stimulated Brillouin scattering

The strong wave-front aberrations compensated by stimulated Brillouin scattering phase conjugate mirror (SBS-PCM) in a high power laser were investigated experimentally. The wave-front fluctuation of the 10 Hz 500 mJ Nd:YAG laser is 0.5λ. Transmitting through a random phase plate (RPP), it increases to 8.6λ. While using SBS-PCM in place of a high reflection mirror, the distortion induced by the RPP is compensated, and the wave-front fluctuation becomes 0.9λ. At the same time, obvious breakdown phenomena in the SBS cell were observed, and the reflectivity is unstable. A rotating wedge plate is introduced into the phase conjugating mirror to make the focus of the SBS cell rotate and optical breakdown is avoided effectively. The reflectivity becomes stable around about 70% and the instability is changed from ±4.1% to ±0.9%. Besides, the compensated wave-front fluctuation is only 0.6λ, which is near to the original wave-front distribution. The results show that the reflectivity of the SBS-PCM is very high and stable when there are no other nonlinear effects such as optical breakdown. Thus the compensating effects for strong wave-front errors are perfect.     

Free vibrations of randomly inhomogeneous plates

Consider a large collection of elastic rectangular plates with random inhomogeneities, but otherwise indistinguishable in any overall sense. An expression is obtained for the natural frequency, μ, of such plates, vibrating freely under simply supported boundary conditions, in the form μ = μ⁽⁰⁾ + ?μ⁽¹⁾ + ?²μ⁽²⁾ + … where μ⁽⁰⁾ is the natural frequency of a homogeneous comparison plate, ? is a small real parameter measuring the degree of inhomogeneity, and the coefficients μ⁽¹⁾, μ⁽²⁾, …, are given explicitly. By constructing geometrically a correlation function for a special type of composite plate, μ⁽¹⁾ is computed and hence, to first order in ?, the variance of μ. The paper concludes with a theorem linking the mean and variance of μ to the volume concentration and geometry of the inclusions in the plate.     

Effect of complex phase plate on tight focusing of azimuthally polarized double ring shaped beam

Based on the vector diffraction theory, the effect of complex phase plate on the intensity distribution of TEM₁₁ mode azimuthally polarized Laguerre–Gaussian beam in the focal region of high NA lens is investigated theoretically. It is observed that a properly designed complex phase plate can generate a subwavelength focal hole having FWHM of 0.332λ with an extended focal depth of 54.4λ. We also observe that by using properly designed complex phase plate generates novel focal patterns including splitting of focal holes and multi focus are obtained. The author expects such investigation is worthwhile for optical manipulation and material processing technologies.     

Femtosecond laser embedded grating micromachining of flexible PDMS plates

We report on the femtosecond laser micromachining of photo-induced embedded diffraction grating in flexible Poly (Dimethly Siloxane) (PDMS) plates using a high-intensity femtosecond (130 fs) Ti: sapphire laser (λ_p = 800 nm). The refractive index modifications with diameters ranging from 2 μm to 5 μm were photo-induced after the irradiation with peak intensities of more than 1 × 10¹¹ W/cm². The graded refractive index profile was fabricated to be a symmetric around from the center of the point at which femtosecond laser was focused. The maximum refractive index change (Δn) was estimated to be 2 × 10⁻³. By the X-Y-Z scanning of sample, the embedded diffraction grating in PDMS plate was fabricated successfully using a femtosecond laser.     

Wavelength shift determination using a dual-path heterodyne Mach-Zehnder interferometer

This paper introduces a dual-path heterodyne Mach-Zehnder interferometer adopted for wavelength shift determinations. In this interferometer, two parallel incident beams are separated into two interference pairs which are then recombined to generate two interference signals. A parallel plate is placed on the path of one wave of an interference pair, so the phase difference of the interference signals is a function of the plate and beam wavelength, and the interferometer is thus able to determine the wavelength shift of the incident beam. A setup constructed to realize the proposed interferometer is described, it shows that the interferometer has a resolution up to 1.1 × 10⁻¹⁰ (λ²/nm), and the experimental results of applying this setup not only agree the validity of the interferometer but also indicate that the interferometer has a stability of 6.5 × 10⁻¹⁰ (λ²/nm).     

A型超导体的近似临界温度公式(Ⅰ)——μ*=0情形

本文用数值解方法从Eliashberg方程计算出超导临界温度T_c,并考察T_c对有效声子谱的依赖关系。在这个研究中,a²F(ω)被取为双δ函数谱,并允许其中的谱参数可以在很宽范围内改变。作者发现在λ<∧区域(即在T_c级数解的收敛圆外),T_c除了依赖λ和矩比外,还依赖T_c级数解的收敛半径倒数Λ;它们之间的关系是有规律的。在这些结果的启示下,本文在μ^*=0情形,用弥合数值解的方法得到一个适用于λ<Λ区域的T_c近似公式。接着,本文作者对吉光达和吴杭生的一篇文章进行了研究,指出:该文提出的超导体分类建议及其工作的主要结论是对的。但其中对决定A型超导体临界温度主要参量问题进行的分析,只适用于这样一些A型超导体,它们的收敛半径倒数Λ或者比λ₀小,或者虽比λ₀大、但λ又小于λ₀,其中λ₀是个依赖谱形状的参量,它的定义在正文中给出。对另一些A型超导体(λ₀<λ<Λ),决定T_c的主要参量不再是λ,而是δ=1/∧^0.5(ω_1/2/ω_log)^5.5λ^1.55。 关键词：     

Hulthén势散射态的解析解

在任意l波的离心项1/r²用λ²e^-λr/(1-e^-λr)²近似表达的条件下,对Hulthén势的径向Schrdinger方程作自变量指数变换,使此转化为超几何微分方程,获得了Hulthén势s波散射态的精确解和非s波散射态的近似解析解.给出了相移的解析表达式和按“k/2π标度”归一化的用超几何函数表示的径向波函数.讨论了解析解的意义.