大气湍流对斜程传输准单色高斯谢尔光束时间相干性的影响

由第一类零阶贝塞尔函数的级数展开推导出波结构函数在任意湍流条件下的近似表达式。由广义惠更斯菲涅耳原理、随高度变化的Hufnagel-Valley湍流廓线模型以及波结构函数在任意湍流条件下的近似表达式,导出了斜程传输时准单色高斯谢尔光束互相干函数的解析式。然后,利用表征光束时间相干性的纵向相干长度(可由互相干函数导出),研究了斜程传输时大气湍流对准单色高斯谢尔光束时间相干性的影响。研究结果表明,准单色高斯谢尔光束的时间相干性在整个斜程传输过程中保持不变。最后,对该结果在物理上给予了定性解释。

大气湍流对斜程传输准单色高斯-谢尔光束空间相干性的影响

由湍流大气中斜程传输时准单色高斯-谢尔(GSM)光束互相干函数的解析式导出了该光束的复相干度.然后,利用表征光束空间相干性的横向相干长度,研究了斜程传输时大气湍流对准单色GSM光束空间相干性的影响.研究结果表明:1)当传输路径偏离水平方向较大(即θ≤88°)时,准单色GSM光束横向相干长度随传输距离均为先迅速增加,后缓慢增加,最后基本保持不变.2)当传输路径接近水平方向(即θ≥89°)时,准单色GSM光束横向相干长度随传输距离均为先增大,达到一个最大值后开始下降并持续减小.3)空间相干性不同的准单色GSM光束在湍流大气中传输一定距离后空间相干性趋于相同.最后,对以上结果在物理上给予了解释.

Formulas, tables, and graphs for trapezoidal reinforced concrete beams

Not available.

Influence of temperature and salinity fluctuations on propagation behaviour of partially coherent beams in oceanic turbulence

A theoretical study of the behaviour of partially coherent beams propagating through oceanic turbulence has been performed. Based on the previously developed knowledge of beam spreading of a partially coherent beam in the atmosphere and the spatial power spectrum of the refractive index of ocean water, we study the normalized root-mean-square width of a partially coherent beam on propagation through oceanic turbulence and its turbulence distance which may be a measure of turbulence resistance. Our analysis indicates that the behaviour of partially coherent beams on propagation may be described by the rate of dissipation of the mean-squared temperature chi(T) and that of salinity chi(S). In terms of a quantity w that defines the contributions of the temperature and salinity distributions to the distribution of the refractive index, chi(S) could be written as a function of chi(T) and w. Therefore, the behaviour of partially coherent beams on propagation can be characterized only by chi(T) for a given w. The results are shown for curved surfaces, from which one can see that partially coherent beams exhibit robust turbulence resistance when the water volume has a smaller chi(T).

Radius of curvature measurements for laser beams: A simple method

A simple method for measuring the radius of curvature of laser beams is introduced. It has been developed to estimate the astigmatic aberration of a diode laser. Compared with the interferornetry, this method is convenient and straightforward. (c) 2005 Elsevier GmbH. All rights reserved.

Analysis of an ultrashort pulsed finite beam diffracted by volume gratings

We obtain analytical solutions of the coupled wave equations that describe the Bragg diffraction of ultrashort pulsed finite beams by a thick planar grating, using two-dimensional coupled wave theory. The diffraction properties for the case of an ultrashort pulsed finite beam with Gaussian profiles in both the time and spatial domains are investigated. The spectral bandwidth of the diffracted beam, the Bragg selectivity bandwidth and the diffraction efficiency of the volume grating are influenced by the geometry parameter and the input bandwidth. Therefore extra attention should be paid to designing optical elements based on volume gratings for use with ultrashort pulsed waves in applications of pulse shaping and processing.

Anisotropic-source-induced changes of the degree of polarization of stochastic electromagnetic beams on propagation

It is shown that stochastic electromagnetic beams may have different degrees of polarization on propagation, even though they have the same coherence properties in the source plane. This fact is due to a possible difference in the anisotropy of the field in the source plane. The result is illustrated by some examples.

Diffraction properties of ultrashort pulsed beams with arbitrary temporal profiles studied with a volume holographic grating

Using modified two- dimensional coupled- wave theory, the diffraction properties of ultrashort pulsed beams with arbitrary temporal profiles are studied with a volume holographic grating. Analytical expressions for the profiles of the transmitted and diffracted beams are obtained. It is shown that the Bragg selectivity bandwidth of the volume grating can be influenced by the geometry parameter. Numerical results are illustrated for three different temporal profiles. For different temporal profiles, the ratios of the diffraction bandwidths to input bandwidths are discussed.

相干模表示的部分相干高斯谢尔光束的相位空间积

与传统的相干激光光束的评价不同, 对部分相干光束质量进行评价时, 不仅要反映其远场发散特性, 而且还要能体现光源本身的部分相干性。根据部分相干光的相干模表示法, 推导了由部分相干光源所产生光束的相位空间积Q。与前人在相干光源情形下得到的结论相比, 得出的相位空简积Q不仅包含各个全相干模基元线性组合的贡献, 而且还有来自不同的全相干模基元之间相互作用的贡献。

Series representation of the Gaussian beam far-field diffracted by annular aperture

Accurate, analytical series expressions for the far-field diffraction of it Gaussian beam normally incident on a circular and central obscured aperture are derived with the help of the integration of parts method. With this expression, the far-field intensity distribution pattern can be obtained and the divergence angle is deduced too. Using the first five items of the series, the accuracy can satisfy most laser application fields. Compared with the conventional numerical integral method, the series representation is very convenient for understanding the physical meanings. (C) 2007 Elsevier GmbH. All rights reserved.