无衍射光束聚焦后的重建与矫正

基于衍射理论分析了无衍射光束聚焦后重建现象.导出重建后的光场分布表达式,数值模拟了重建光束的光强分布.结果表明,重建光束中心光斑较聚焦前的无衍射光束中心光斑大,而且重建后的光束有较大的发散角,光束随着传输很快扩散,光强迅速衰减.此类光束的应用受到限制.利用另一正透镜对重建后的光束加以矫正.并且由几何光学知识,得到了改变重建光束参量的方法,研究结果拓宽了无衍射光束的应用.用体视显微镜和CCD照相机组成的系统拍摄光束强度分布,实验结果与理论计算相吻合.     

红外系统后向反射光的光强研究

 根据衍射光学理论分析了红外系统后向反射光强的分布,反射区域可以分成近场传输区域、菲涅耳衍射区域和夫琅和费衍射区域。在菲涅耳衍射区域内,反射光斑中心光强是呈明暗变化的,反射光斑中心光强在0～1km内剧烈振荡,1～3km之间达到峰值,然后随传输距离的继续增加,反射光斑中心光强逐渐减小。在夫琅和费衍射区域内,光斑图像中央是亮光斑,周围环绕着明暗交替的圆环。     

直尺衍射现象及分析

衍射是光的波动性的一个重要特征,而光栅衍射则是其中一类常见且重要的衍射现象.当激光束入射直尺边缘或表面时会出现半圆形衍射光斑,其产生机理并不清楚.针对直尺边缘与表面的半圆形衍射光斑,本文理论结合实验分析了其产生机理.研究发现,当直尺表面或侧面存在规则的类光栅结构时,其衍射光斑为半圆形.利用标准二值光栅模型分析了直尺衍射问题,发现半圆形衍射光斑起源于多套光栅衍射的叠加.     

关于光学仪器分辨本领的几个问题──备课扎记

光学仪器的分辨本领,通常是由夫琅和费衍射求得最小分辨角 但是,我们经常会遇到一些形式略异的公式,特别是式中的系数有的是0.77或0.5.此外,(1)式中的a究竟应该用光学仪器的哪一个通光孔的半径?在讨论显微镜的成象时,为什么也可以用夫琅和费衍射计算分辨极限呢?这些问题都曾经是使笔者在备课中感到困惑的问题. 1.光学仪器的成象与夫琅和费衍射 由于衍射现象,即使光学仪器不存在象差,物面上的一个点在象面上也会形成一个光斑.如何计算这个光斑的大小和强度分布呢? 在圆孔的夫琅和费衍射中,可以算得光斑的强度分布为利用贝塞耳函数的性质,不难…     

布拉格衍射下半导体激光光强分布实验探讨

通过控制变量法,探究了声光效应中布拉格衍射下不同超声波频率、功率以及是否载入调制信息下衍射光斑的光强横向分布.并用MATLAB软件拟合了0级和-1级衍射光的光强分布图,将实验结果与理论解释进行对比分析.     

双轴棱锥产生长距离近似无衍射光的新技术

提出了一种利用会聚透镜、轴棱锥等简单光学元件产生长距离近似无衍射光的新技术. 分别利用几何光学和衍射理论分析了该方法产生长距离近似无衍射光束的原理, 通过软件模拟了长距离近似无衍射光束的形成过程,得出了该光束在不同距离处的横向光强分布. 模拟结果显示该光束在较长距离处的横向光强分布满足Bessel分布. 从实验上获得了传播距离长达80 m、中心光斑发散角约为0.12 mrad的近似无衍射光束, 相比于国外学者最近的研究成果(Belyi et al. 2010 Opt. Exp. 18 1966)将传播距离延长了50多米,而光束发散角压缩了22倍.实验中, 对光束沿光轴传播时在不同距离处的光斑进行了拍摄,所得实验结果与理论分析基本符合.     

高能激光环形光束近场和远场传输特性

为满足高能激光环形光束在近场区和远场区的实际应用需求,从电磁波衍射积分方程出发,推导了环形光束光场分布和远场光强分布表达式,并对光场分布和光强分布进行了分析,得到光强分布与高斯光束的有限孔径大小、中心遮拦比和传输距离的关系.引入大气湍流场景,采用相位屏法对环形光束在不同湍流强度下的大气传输进行了数值模拟和分析,研究了受大气湍流影响远场光斑畸变、光斑破碎、光束扩展和漂移等的增强现象.最后开展了环形光束近场区大气传输数值模拟和实验,结果表明:随着传输距离的增加,光斑中心光强越来越强,光斑逐渐趋于均匀,平均光强呈类高斯分布,近场区环形光束扩散和光斑畸变现象受大气湍流影响而增强.     

高斯光束非对称照明锥镜时的衍射场分布

采用光的干涉方法研究了高斯光束非对称照明锥镜时的衍射场分布。数值模拟结果发现,当光束中心偏离锥镜的轴线时,衍射场的分布不再呈对称状分布,尤其在相干区。照明光束的偏离量越大,衍射光斑偏离锥镜的轴线越多。衍射光斑的平均光强随照明光束偏离量的增加迅速减小。这些结果对于锥镜在光镊和光学元件的机械排列等应用中具有一定的指导意义。     

新型棱镜产生近似无衍射线结构光

为了改善三角棱镜系统产生近似无衍射线结构光的能量均匀分布在若干条光斑上,不适合直接应用于三维表面测量且中心光斑对能量利用率较低的问题,提出了一种新型光学元件.该元件在三角棱镜的基础上,通过在其底部胶合一个与原三角棱镜底面大小相等,横截面为等腰梯形的凸台制成.采用几何光学的理论对新型光学元件的光束变换特性进行分析,结果表明其可以等效为两个不同底角三角棱镜的组合,平面光束通过新型光学元件后将产生中心光斑较强的近似无衍射线结构光.由衍射积分理论分析和模拟了新型光学元件后的空间光强分布特性.仿真的结果表明,衍射积分分析的结果与几何光学分析的结果是一致的:新型光学元件可以产生一种性能更好的近似无衍射线结构光.并且通过改变棱镜的结构参量,能够方便地调节光束的中心光斑尺寸、近似无衍射范围等参量.     

基于同步多曲面法的发光二极管机器视觉照明设计

为了改善三角棱镜系统产生近似无衍射线结构光的能量均匀分布在若干条光斑上,不适合直接应用于三维表面测量且中心光斑对能量利用率较低的问题,提出了一种新型光学元件.该元件在三角棱镜的基础上,通过在其底部胶合一个与原三角棱镜底面大小相等,横截面为等腰梯形的凸台制成.采用几何光学的理论对新型光学元件的光束变换特性进行分析,结果表明其可以等效为两个不同底角三角棱镜的组合,平面光束通过新型光学元件后将产生中心光斑较强的近似无衍射线结构光.由衍射积分理论分析和模拟了新型光学元件后的空间光强分布特性.仿真的结果表明,衍射积分分析的结果与几何光学分析的结果是一致的:新型光学元件可以产生一种性能更好的近似无衍射线结构光.并且通过改变棱镜的结构参量,能够方便地调节光束的中心光斑尺寸、近似无衍射范围等参量.     

对实屏的夫琅禾费衍射中心亮点(亮纹)的半定性半定量论证

光经圆盘、细丝等实屏衍射后,衍射光场中其几何阴影中心有不为零的光强分布.显然这是阐述光的波动性的最好例证,它比圆孔、单缝之类的光孔衍射更具说服力.然而对圆盘等的衍射中心亮点(如泊松点)的论证通常都是从菲涅耳衍射出发,但是在绝大多数非物理类专业的大学物理中,对光的衍射的具体分析都只涉及夫琅禾费衍射,因而给学生对于上述问题...     

Angular splitting of the Bragg diffraction order in an acoustooptical modulator due to a frequency-modulated acoustic wave

Effects of angular splitting of the Bragg diffraction order arising in light acoustooptical diffraction by a frequency-modulated acoustic wave are considered. These effects occur when the size of the light spot in the acoustooptical interaction zone exceeds the characteristic spatial period of the modulating function. The Bragg diffraction order is found to be split into several beams. The directions of the additional beams, their number, and intensities are determined by the modulation parameters. In particular, there occurs a situation where the diffracted field consists of three beams of equal intensity spaced at a distance approximately equal to the diffraction divergence of the incident beam and the diffraction total efficiency is of the order of 100%. Therein lies the difference between this diffraction regime and the case where several independent acoustic waves are generated in the interaction domain and the diffraction total efficiency is limited to the intermodulation arisen. The effect is used in design of modulators for systems of image plotting with the help of high-power lasers.     

Airy beam laser

A method to design lasers that emit an arbitrary beam profile is studied. In these lasers, output-coupling is performed by a diffraction grating that imposes a phase and amplitude distribution onto the diffracted light. A solid-state laser emitting beams with a two-dimensional Airy intensity profile is demonstrated both theoretically and experimentally. In this case, the diffraction grating adds a transverse cubic phase to the diffracted light. An Airy beam is obtained by performing optical Fourier transform of the out-coupled light. The laser beam profile and power characteristics are shown to agree with theory.     

平面波经小圆孔衍射的轴上光强特性

基于精确的衍射场公式和横截面上光强的精确表述，分析讨论了单色平面光波经小圆孔衍射后，其衍射光束轴上光强的最大值以及轴上光强极值的数目和小圆孔半径的关系；并且由此考察了一般的菲涅耳数计算公式的使用条件。     

Reflection holographic lens having nonspherical wavefront designed by a microcomputer

A design of a reflection holographic lens with nonspherical wavefront is described, which is based on a ray-tracing program and a simple search algorithm suitable for a microcomputer. The optimized wavefront is encoded into a computer- generated hologram (CGH). The reflection holographic lens with the optimum wavefront produced by CGH reduces the rms spot radius at large field angles, and allows for a compact folded system and for Bragg diffraction into a single order. Experimental results are shown. Helpful data on the diffraction efficiency and the spectrally diffracted intensity of reflection holograms are presented.     

衍射光学器件光线追迹公式的实验验证

本文介绍了一种衍射光学器件光线追迹的方法，并给出了计算公式。作为验证，在实验室里制作了具有连续相位的体全息器件，将其实际再现光斑与计算点列图进行比较。构造透射体全息片的物光为离轴的球面波，始于轴外点Ａ（０，１３２ｓｉｎ８°，－１３２ｃｏｓ８°），参考光为平面光束，其与Ｚ轴夹角为１７°。激光器采用氩离子激光器（Ｓｐｅｃｔｒａ－ｐｈｙｓｉｃｓＭｏｄｅｌ２０２０），波长４８８ｎｍ；干板感光胶为重铬酸明胶（ＤＣＧ），胶层厚为１５μｍ；通光口径３０ｎｍ。测试时把全息片放在干板的位置。挡住物光，让再现光以和参考光路相同的路径平行入射到全息片上，在全息片后垂直光轴放置毛玻璃片，平行光轴移动毛玻璃片，可观察到－１级衍射光的变化。在距离原点的距离分别为（ａ）４０ｍｍ，（ｂ）７０ｍｍ，（ｃ）８７ｍｍ，（ｄ）９５ｍｍ的地方用ＣＣＤ拍摄了衍射光的形状，与程序计算的点列图在形状和大小上都吻合     

Diffraction of light by an acoustic wave with three frequency components

Collinear light diffraction by three-frequency sound is investigated theoretically. The amplitude distributions of transmitted and diffracted light waves along the cell are calculated for different amplitudes of sound signals. The dependence of the intensity of principal diffraction peaks on the frequency difference between acoustic signal components is studied for different amplitude ratios of these components. It is shown that the character of this dependence for a wave being in synchronism differs substantially from that for two other waves characterized by detuning. The dependence of the amplitudes of principal and parasitic diffraction peaks on the efficiency of acoustooptical interaction is investigated. It is demonstrated that parasitic sideband components in diffracted light can play a considerable role if the diffraction efficiency is sufficiently high and exceeds 80%.     

菲涅尔多缝衍射的数值计算

本文直接由菲涅尔一基尔霍夫衍射积分公式出发,通过数值积分的方法,计算菲涅尔单缝、双缝以及多缝衍射的光强分布,绘制出其相应的光强分布曲线.同时给出了计算菲涅尔多缝衍射的光振动分布的具体表达式.研究结果对于理解菲涅尔衍射现象具有重要的理论参考意义.     

Plane-wave analysis of the near field of light diffracted by ultrasound.

Although the phenomenon of light diffraction by ultrasound has been studied very extensively during the last 40 years, almost all investigations were concentrated on the individual far field (Fraunhofer) diffraction orders. In the present paper, the basic theory is developed for studying the near field (Fresnel region) of light diffracted by an arbitrary plane ultrasonic wave and the fundamental periodicity properties are stated. The general plane-wave theory of Raman-Nath has been taken as a starting point. From the analysis, the near field of the diffracted light is seen to be highly sensitive to variations of the ultrasonic amplitude and this feature provides a useful technique for observing weak ultrasonic waves. In particular, for the specific case of Raman-Nath-type diffraction, a procedure is presented allowing the reconstruction of the time waveform of the ultrasonic wave from the diffracted light intensity signal.