激光加工中光化学作用的检测分析方法

在基于激光加工各种材料过程中存在的光热作用和光化学作用的基础上,综述了激光加工过程中光化学作用的检测分析方法.对光化学作用结果的检测主要通过对激光作用后材料表面的结构、成分、微观形貌、物理化学特性等的变化进行分析;而对光化学作用过程的检测则采用具有时间分辨尺度的质谱仪或光谱仪等对激光加工过程中产生的分子碎片和带电离子的...     

探测系统噪声对激光束束宽测量的影响

讨论了由于探测系统噪声原存在,对目前广泛采用的二阶矩束宽定义的激光束空域参数测量系统的影响,并给出实际测量系统设计时减少噪声影响的方法。     

激光束角漂移对双频激光直线度测量的影响

利用惠更斯关于波面传播的理论，分析计算了双频激光渥拉斯顿棱镜直线度测量系统中激光束角漂移以及渥拉斯顿棱镜和双面反射镜倾角对测量精度的影响，得到了相应的结论。     

激光诱导荧光对激发光束入射角的依赖关系

研究了一种应用较广的机油的激光诱导荧光（LIF）对激光入射角的依赖关系,结果表明,发射谱的形状基本不随入射角改变,荧光强度则随入射角α的增大而减小,当α＜45度时,这种变化较为明显,并于α=0度时的50％左右,此后继续增大α,光的衰减变缓。     

Propagation of a Non-Gaussian Laser Beam in SELFOC Fibres

In this communication we have presented an analysis of the propagation of a laser beam operating in a TEM₀₁ mode, in a medium of varying dielectric constant. The cylindrical and conical optical fibre guides have been considered. The results have been put in a form suitable for numerical computation.     

Reshaping of a Divergent Elliptical Gaussian Laser Beam Into a Circular, Collimated, and Uniform Beam With Aspherical Lens Design

In this paper, we present a specific optical system of two aspherical lenses designed to circularize, collimate, and expand an edge-emitting semiconductor laser beam and transform its irradiance distribution from Gaussian to a uniform-square distribution for possible application in light detection and ranging sensors. It is verified that the diffraction effects are negligible so that geometrical ray optics is used to design this optical system. To accomplish the design, the source beam profile is decoupled into two independent beam profiles represented in two transverse directions. Analytical equations specific to this lens system are derived and MATLAB is used to solve these equations and simulate a design example. Results are presented for a specific example.      

聚焦离子束系统在微米/纳米加工技术中的应用

聚焦离子束系统是微细加工和分析的主要技术之一,是一个完美的微米/纳米技术研究平台.简述了聚焦离子束系统的组成和主要功能,着重介绍了近年来该技术在离子束刻蚀、反应离子束刻蚀、离子束辅助沉积、离子注入、微区分析、掺杂和成像以及无掩膜曝光等微米/纳米加工领域的应用,并对未来的发展前景进行了简要分析.     

Measurement of Atmospheric Turbulence Induced Intensity Fluctuations in a Laser Beam

We report measurements of the statistical properties of the intensity fluctuations in a He/Ne laser beam which had propagated 1·125 km through the earth's atmosphere. The beam size was such that the beam propagated as a spherical wave, and atmospheric conditions such that most measurements were made in the ‘saturation’ region (β₀ ～ 1-4). We found (1) that the variance of the intensity was considerably larger than that previously reported for plane wave propagation, and (2) that the probability distribution of the intensity and the derived moments were close to the K-distribution and its moments. The origin and significance of the K-distribution in atmospheric propagation is considered. Photon counting techniques were used for all measurements.     

Optical Frequency Metrology of an Iodine-Stabilized He-Ne Laser Using the Frequency Comb of a Quantum-Interference-Stabilized Mode-Locked Laser

We perform optical frequency metrology of an iodine-stabilized He-Ne laser using a mode-locked Ti:sapphire laser frequency comb that is stabilized using quantum interference of photocurrents in a semiconductor. Using this technique, we demonstrate carrier-envelope offset frequency fluctuations of less than 5 mHz using a 1 s gate time. With the resulting stable frequency comb, we measure the optical frequency of the iodine transition [¹²⁷I₂ R(127) 11-5 i component] to be 473 612 214 712.96 ± 0.66 kHz, well within the uncertainty of the CIPM recommended value. The stability of the quantum interference technique is high enough such that it does not limit the measurements.     

Impulse Modeling of the Rayleigh Wave Propagation Generated by a Spherical Focused Transducer

In order to characterize materials locally by means of the Rayleight wave analysis, a new modeling of acoustic microscopy in the case of an impulse excitation is presented. The usualV(z) representation established for a given frequency component, is extended to the case of a broadband excitation of the transducer. Therefore, the time-dependant acoustic response of the material,s(z,t), is mainly composed of two echoes: the specular and the Rayleigh contributions which are resolved in time. In the first part, we demonstrate that the acoustic response can be represented by the time convolution product between the acoustic signal detected at the focus on an ideal reflector, and a function depending onz andt variables. This last function is connected to the tranducer emission profile, which includes the diffraction effects, and the reflectance of the material. In the second part, the modeling is discussed with regard to experimental data on several materials and takes into account the attenuation phenomena. Experimental results and computations are shown to be in a good agreement.     

用Hartmann－Shack传感器测量激光束的波前相位

Ｈａｒｔｍａｎｎ－Ｓｈａｃｋ传感器已经用于自适应光学系统。它可以同时探测出一束光的振幅和相位信息。通过一个位置传感器，比如ＣＣＤ，它就可以成为一种对光学系统和光束的静态和动态质量诊断的有力工具。从Ｈ－Ｓ波前传感器的输出（波前斜率和近场强度分布），就可以推算出远场特点，如ＰＳＦ和ＯＴＦ。本文将介绍波前重构的理论分析和远场特征评估。同时也给出了光束质量的静态和动态的测量结果。     

聚焦离子束在微纳尺度材料力学性能研究中的应用

微纳尺度材料是指外观尺寸或其基本构成单元在10nm到10μm之间（以下简称微纳尺度）的材料或器件。个案、定性的研究表明微纳尺度材料有以下特性：其性能不能通过外推基于宏观块体材料的知识体系得到,传统的力学测试工具和方法无法满足对微纳尺度材料进行测试的要求,微纳尺度材料通常在多场耦合条件下服役。这些特性要求研究工作者持续不断地寻找和研发新的工具以期实现对微纳尺度材料的可控制备,高通量观测、操控和定量测量。双束聚焦离子束技术不仅因具有纳米级的空间分辨率而具备对微纳尺度材料的高质量成像和动态监测,而且具备纳米分辨率的定点刻蚀、诱导沉积等功能。因此,双束聚焦离子束成为研究微纳尺度材料力学性能的有力工具。综述了近年来聚焦离子束技术在微纳尺度材料类力学性能研究中的应用,并讨论了其局限性和发展趋势。     

Harnessing Photochemical Shrinkage in Direct Laser Writing for Shape Morphing of Polymer Sheets

Structures that change their shape in response to external stimuli unfold possibilities for more efficient and versatile production of 3D objects. Direct laser writing (DLW) is a technique based on two‐photon polymerization that allows the fabrication of microstructures with complex 3D geometries. Here, it is shown that polymerization shrinkage in DLW can be utilized to create structures with locally controllable residual stresses that enable programmable, self‐bending behavior. To demonstrate this concept, planar and 3D‐structured sheets are preprogrammed to evolve into bio‐inspired shapes (lotus flowers and shark skins). The fundamental mechanisms that control the self‐bending behavior are identified and tested with microscale experiments. Based on the findings, an analytical model is introduced to quantitatively predict bending curvatures of the fabricated sheets. The proposed method enables simple fabrication of objects with complex geometries and precisely controllable shape morphing potential, while drastically reducing the required fabrication times for producing 3D, hierarchical microstructures over large areas in the order of square centimeters.     

Modeling Ultrasonic Pulse-Echo Signals from a Flat-Bottom Hole in Immersion Testing Using a Multi-Gaussian Beam

This paper proposes an ultrasonic measurement model that can predict the pulse-echo signals from a flat-bottom hole in an isotropic, homogeneous solid specimen immersed in water in a computationally efficient manner. To develop such a model, a measurement model approach is adopted based on two important assumptions: the paraxial approximation for the transducer beam and the small flaw assumption for the flat-bottom hole. The modular model that results from these two assumptions contains three terms: a diffraction correction term, a far-field scattering amplitude term and a system efficiency factor term. The diffraction correction is defined based on a multi-Gaussian beam model which allows the rapid evaluation of the wave field incident on the hole. The far-field scattering amplitude of the flat-bottom hole is obtained using the Kirchhoff approximation together with the small flaw assumption. The system efficiency factor is determined by deconvolution of an experimental front surface reflection signal by a reference reflector model. Here, the contribution of each of these three terms to the overall measurement model are described in detail and the accuracy of the proposed model is verified by the comparison of the model-based predictions to experiments.     

基于声光偏频法的激光频率无调制锁定

为了进一步提高1.5 μm波段激光器的频率稳定性,利用声光调制器(AOM)的频移特性使激光发生频移,将乙炔(~(12)C_2H_2)v_1+v_3带的P9支吸收峰作为参考频率,通过两条频移的吸收谱线产生类色散鉴频曲线,实现对外腔半导体激光器的无调制频率锁定.实验中把以前直接对激光器的调制转移到声光调制器上,避免了直接调制所引入的额外噪声,通过闭环锁定,50 s内典型的频率起伏达到5.8 MHz以内,激光器的频率起伏较自由运转时明显得到抑制,实现了激光频率的稳定.     

Radial Structure of the Temperature Field in Biological Tissue under Irradiation by a Laser Beam

Using the previously developed method, we have obtained analytically the Green function in the time and radial coordinates for the problem on medium heating under external irradiation. On this basis, the radial structure of the temperature field in the biological tissue has been investigated. The influence of the radial diffusion of light on the thermal conditions of the tissue has been estimated, and it has been shown that at fairly large times after irradiation such diffusion can be neglected. Examples of radial and depth temperature distributions at various optical parameters of the tissue are given. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 4, pp. 82–86, July–August, 2005.     

激光功率变化引起的非线性误差对纳米测量精度的影响

拍频干涉法可用于纳米，亚纳米级精度的位移测量，其测量不确定度主要敢决于单位频差－位移当非线性，本文对影响非线性的因素进行了试验分析和理论计算，结果表明，非线性范围为0.07-1.5nm.