抛物型发散GRIN纤维透镜的特性

应用矩阵光学方法,研究了抛物型梯度折射率(GRTN)纤维透镜的成像规律,导出了主平面位置、主焦距等光学参数的公式,并与其它类型的发散GRIN纤维透镜作了比较。     

球面端面抛物型发散GRIN透镜的光束光学理论

本文基于高斯光束传播理论,研究高斯光束经端面为球面的抛物型发散梯度折射率纤维透镜的变换特性,结果可用于梯度折射率激光束变换元件的设计。     

The fabrication of three-dimensional nano-structures by defocused electron beam energy

We demonstrate a novel method to fabricate three-dimensional structure with various shapes using defocused electron beam lithography (DEBL) for optical elements. In this study, we experimentally analyzed the relationship between the shape profiles of exposed patterns and defocusing length by varying parameters for e-beam lithography.Through these experiments, we found out that the shape profiles of exposed patterns depended on the defocusing length at the specific conditions in the e-beam lithography. This is due to the fact that the distribution and intensity of electron beam energy are changed by the defocusing length degree in the DEBL. These results allow the fabrication of three-dimensional (3D) structures with various shapes for optical elements by varying the defocusing length under the proper conditions of e-beam lithography. Based on these results, we can fabricate the 3D patterns with hemispherical shape for nano lens array and nano cone shape for SERS (surface enhanced Raman spectroscopy) and optical diffraction grating patterns with nano scale depth and width.     

抛物型发散梯度折射率纤维透镜光学特性的限制

从近轴条件下的光线轨迹方程出发,导出了计算抛物型发散梯度折射率纤维透镜有效长度的方程式,并讨论了该纤维透镜大端、小端对目标成像的孔径和视场。     

Laser Refining of a Surface Layer with Silicon Carbide

The article discusses the effect of adding silicon carbide by laser remelting of low-carbon steel. Tests in laser remelting were carried out with energy inputs ranging between 10 and 80 J/mm² with the most favorable degree, i.e., 30%, of overlapping of individual trace. Sufficient energy input was necessary to dissolve silicon-carbide with iron. A microchemical analysis of the remelted layer confirmed the dissolution of silicon carbide and formation of a smaller portion of martensite (10-20%) and of suesite Fe₃Si (65-80%). It was found that the test-specimen deformation was smallest with the laser-beam in the zig-zag motion. The surface was also assessed visually. The choice of adequate remelting conditions reduced, i.e., prevented, the occurrence of cracks and other defects. The influence of energy input and the mode of laser-beam travel on the efficiency of remelting, i.e., refining, was described by a ratio of the width of the remelted surface layer to its depth, which should amount to around 5:1.     

显微散焦粒子识别与追踪测速

根据三孔挡板散焦成像的原理,使用高速散焦显微粒子测速装置开展三维显微粒子追踪测速研究。在粒子散焦像识别的过程中利用了其对应三角模型相似的特点,通过散焦像斑灰度呈二维高斯分布特征计算其质心。在粒子三维位置测量算法分析的过程中选择了多达29颗的样品粒子,对29组不同深度的数据采用线性拟合的方式进行粒子深度方向的标定,并用二元多项式对870组数据拟合获得了关于粒子平面位置漂移的补偿函数。针对长直微通道内雷诺数Re分别为0.05和0.1的流场进行了验证性测量,采用20′0.4显微物镜,使用高速CMOS相机对直径为2mm的粒子进行追踪。结果显示,计算出的示踪粒子速度分布与数值仿真曲线吻合良好。     

激光主动探测系统的探测能力分析

为了能够准确获取"猫眼"光学系统激光反射回波信号方向性和发散度的信息,基于光学系统"猫眼"效应和高斯光束的变换规律,依据激光大气传输的衰减和强度闪烁特性,给出了激光主动探测系统回波能量衰减和起伏的数学模型.结合野外试验分别对焦平面光学系统和离焦光学系统的关键指标进行了工程计算、分析论证和比较,结果表明:在激光主动探测系统探测识别时,可根据回波信号强度来识别不同类型的目标:同时对激光在大气传输中能量的衰减和光强的起伏进行了工程计算和分析论证,结果表明:大气湍流会大幅度降低激光主动探测系统的探测距离.     

High quality full ablation cutting and stealth dicing of silica glass using picosecond laser Bessel beam with burst mode

Glass cutting is widely used in many fields, such as aerospace and integrated electronics. To meet requirements of high-quality glass cutting, methods of full ablation cutting and stealth dicing of silica glass using picosecond laser Bessel beam are studied in this paper. Position synchronized output function of laser source and burst mode (BM) can flexibly adjust drilling spacing and the number of sub-pulses during processing. Through experimental research and theoretical analyses, effect of hole spacing, BM, laser power, and defocusing distance on the roughness of the cross-sections of cutting samples are investigated. The optimal combination of full ablation cutting parameters is obtained with the minimum roughness of the cross-section of 355 nm. To expand the application range of Bessel beam glass cutting, stealth dicing process is developed. Process parameters selection strategy of stealth dicing is obtained. Main parameter that affects the effect of stealth dicing is the defocusing distance. Aforementioned methods may provide simple, efficient, and high-quality full ablation cutting and stealth dicing technologies for glass materials.     

Optical emission monitoring for defocusing laser percussion drilling

This paper presents a novel method for controlling the laser-drilling process for a hole by monitoring induced plasma emission. The variation of light brightness from laser-induced plasma is used as an indicator to control laser percussion drilling. Through on-line plasma emission acquisition and analysis, we obtain the positive association between the increased depth and the optical signal output. A coaxial photodiode is used to estimate the brightness levels of laser-induced plasma. The above constitute an inexpensive and practical on-line feedback system that can be easily implemented in the laser systems. All of the processing work is performed in air under standard atmospheric conditions without gas assist. The acquired signal for drilling could also be used as an input to a focus point process control scheme. Moreover, the technology demonstrates the feasibility to develop an automated laser micromachining system. Experimental results show that drilling efficiency was increased 47% by applying the proposed defocusing laser percussion drilling.     

基于运动和散焦线索的深度提取研究

随着立体图像在社会各个领域的发展与普及,三维资源的需求逐步提升,而将二维图像转换为三维图像是解决三维资源稀缺的重要手段。二维图像三维化技术的关键在于深度信息的获取。分析了两种重要的深度提取线索,运动线索和散焦模糊线索。为了弥补这两个线索在深度提取的局限性,提出了两种线索的深度融合策略。实验结果表明,这两种线索采用分段线性融合的方法能提高生成深度图的质量。