方形自聚焦透镜的折射率分布研究

为了获得方形自聚焦透镜的折射率分布,提出了一种求解其折射率分布的半经验方法。该方法利用圆形边界条件下获得的扩散方程的解去近似方形边界条件下扩散方程的解,该近似解中的4个待定系数用雅明干涉法测得的方形自聚焦透镜4个位置点上的折射率来确定。该方法避免了在方形边界条件下求解扩散方程的复杂过程,得到的半经验公式形式简单、计算方便,利用半经验公式计算得到的折射率与实验结果吻合得较好,二者之间的最大相对误差为0.94%,平均相对误差不超过0.3%。该公式为以后研究方形自聚焦透镜阵列成像问题提供了可供参考的理论依据。     

高功率固体激光系统中的"热像"效应

"热像"效应是制约高功率激光系统,特别是惯性约束核聚变(ICF)激光驱动器安全运行和提高输出功率的瓶颈因素之一。在某些条件下,往往系统运行在典型的损伤阈值功率之下时,某些光学元件也会因为"热像"效应的存在而意外地遭受损伤。总结介绍了近年来关于"热像"效应研究的新进展,包括"热像"形成的衍射理论模型、薄片近似下的解析理论分析结果、厚介质及级联介质情况下激光"热像"的演化规律、多散射点形成"热像"的特点以及"热像"效应的抑制方法等。最后指出理论及实验上尚待进一步解决的问题。     

Propagation of Hermite-cosh-Gaussian laser beams in non-degenerate germanium having space charge neutrality

In this paper, we analytically investigate Hermite-cosh-Gaussian (HChG) laser beam propagation in non-degenerate germanium having space charge neutrality for the first three mode indices. The field distribution in the medium is expressed in terms of beam-width parameter f and decentred parameter b. The differential equations for the f parameter are established by a parabolic wave equation approach under paraxial approximation. Analytical solutions are obtained under the condition R _n < R _d , where R _n is the self-focusing length and R _d is the diffraction length. The behaviour of the f parameter with the dimensionless distance of propagation η for various b values is examined by numerical estimates. The results are presented graphically.     

自聚焦图像边缘探测器

介绍了一种自聚焦滤波器,它是用二元光学的方法把匹配滤波器和菲涅耳波带片组合在一起,制成一个具有自聚焦功能的位相型元件,用于探测图像边缘信息时可极大地简化光路,并且调节方便,同时提高了衍射效率.讨论了用这种组合滤波器探测图像边缘的原理,介绍了元件的制作方法,并给出了实验结果.     

Signal emitted from plasma during electron-beam welding with deflection oscillations of the beam

The oscillations of a signal, collected by a ring electrode with +50 V potential, situated in the plasma over the welding zone during electron beam welding (EBW) with local beam deflection oscillations were studied. Samples of chrome-molybdenum steel were processed. The frequencies of the beam oscillations varied between 150 and 1400 Hz and their trajectories were the simplest: along and across the joint. The position of the beam focus was changed. Fluctuations of the emitted plasma current by coherent accumulation of the signal amplitudes were analysed and the probability for instability excitations in the keyhole was estimated. This method allows the study of the random instability processes at the interaction of the beam with the keyhole wall and bottom. A time shift between the maxima of the function derived from the coherent accumulation and the extremes of the deflection coil current was found. This shift depends on the beam focus position. In addition, at longitudinal beam oscillations, and at variations of the focus position a difference of the extreme values of the studied signal was observed. At the lowest values of the current of the focusing electromagnetic lens, the differences between the maxima of the probabilities for excitation of the plasma signal oscillations in the moments at beam bombardment on the front and trailing walls of the keyhole in the molten pool were about 30%, while the beam over-focusing decreased these differences. For beams situated at the central part of the keyhole, the collected signal was minimal. From the observations of spikes in the weld root, at EBW with deflection oscillations, it was concluded that self-focusing of the beam in the bottom part of the keyhole in the cases of the most focusing positions was occurring.     

傍轴黎曼几何光学应用——光束自聚焦

利用光流体模型 ,计算模拟了激光束的自聚焦传输特性 ,得到与实验相一致的结果。     

时反法用于被动通信的研究

时反法是一种新颖的自适应聚焦技术，它可以使声信号在未知环境下实现时空聚焦。海洋是一个复杂多变的信道，它会使声信号产生畸变从而降低通信系统的工作性能。分析了时反法的理论基础，并对其用于浅海被动通信进行了仿真研究。仿真结果表明，它可以使信号实现重构，消除码间干扰，提高通信系统的性能。     

变形高阶贝塞尔光束的传播和自成像效应

从产生高阶贝塞尔光束的典型光路着手, 通过将高阶贝塞尔光束分解为高阶贝塞尔余弦光束和高阶贝塞尔正弦光束, 利用柱坐标下的Collins公式,分析了变形高阶贝塞尔光束的解析表达式和在自聚焦透镜中的传播。得到了变形高阶贝塞尔光束的一般解析表达式,自由空间的自成像过程,和在自聚焦透镜中传播的特点以及它们在高阶贝塞尔余弦光束和高阶贝塞尔正弦光束波数横向分量差异为0.005 K时的数值模拟。结果证实了变形高阶贝塞尔光束具有无衍射特性及自成像效应。     

自聚焦变栅距光栅设计、制作及特性研究

利用变栅距光栅的衍射光束自聚焦特性,设计和制作了变栅距透射光栅,并对其自聚焦特性进行了研究.采用变栅距光栅的自动生成宏文件程序,优化设计了变栅距光栅的栅距变化.采用光栅扫描电子束光刻的方法制作了中心线数为300 1/mm、适用于355 mm波长的自聚焦变栅距变狭缝光栅.使用三倍频Nd:YAG激光器,研究了制作的变栅距光栅的聚焦特性,并与对氦氖激光的聚焦特性进行了比较.结果表明,主动式设计的变栅距变狭缝自聚焦光栅可以大幅提高衍射光强度和分辨本领,具有重要的应用价值.