激光内切割技术

本文提出了一种全新的快速成型方法－激光内切割技术。阐述了基于RP技术思想的激光内切割技术原理,并就激光光束的聚焦和调Q特性分析了激光内切割技术可行性,最后讨论了由激光功率、扫描速度等因素引起的不同激光功率密度与材料的相互作用及影响。     

低压水射流激光复合切割Al2O3 陶瓷的研究

针对激光切割Al2O3 陶瓷存在热裂纹、大量熔渣等问题,提出了低压水射流激光复合切割陶瓷技术,并将这种工艺与普通激光切割进行了对比,结果表明低压水射流激光复合切割陶瓷可以大大减少陶瓷切缝的熔渣、避免热裂纹。主要研究了辅助气体压力、激光脉冲能量和激光重复频率对水射流激光复合切割Al2O3 陶瓷质量的影响规律,发现水射流存在时,辅助气体压力主要起到吹除切割头处水珠的作用,激光脉冲能量或激光重复频率增大、烧蚀材料增多,当烧蚀材料不能及时被射流冲除就形成了熔渣的累积,影响陶瓷切割质量。     

晶圆激光切割技术的研究进展

综述了半导体领域晶圆切割技术的发展进程,介绍了刀片切割技术、传统激光切割技术、新型激光切割技术及整形激光切割技术的特点、工作原理和优缺点以及国内外使用晶圆切割技术获得的研究成果及其应用前景.与刀片切割技术相比,激光切割技术具有切割质量好、切割速度快等优点.详细介绍了以进一步改善晶圆切割质量和提高切割速度为目的的几类整形激光切割技术,包括微水导激光切割技术、隐形切割技术、多焦点光束切割、“线聚焦”切割、平顶光束切割和多光束切割等.随着技术的不断完善、切割设备的不断成熟,整形激光切割技术在未来的晶圆切割领域将具有广阔的应用前景.     

激光切割系统功率实时控制研究

激光功率对切割质量具有重要的影响,功率过大容易产生过烧现象。为了保证切割质量,研究了激光功率与切割速度的关系,基于可编程多轴运动控制器提出了激光功率实时控制的方法,使用开放性编写应用程序进行串口通信调整功率的方式实现激光功率的实时控制。采用这种方法进行激光切割试验,当激光功率能够随切割速度实时变化时,可以避免烧角现象。结果表明,此方法可以有效地提高切割质量,并且保证了激光切割的效率。     

激光旋转切割石英管设备研制及其工艺研究北大核心CSCD

为了实现将密封石英管内器件取出的目的,设计研制了一套激光旋转切割设备。由于石英管内密封晶圆类易碎器件,为了不产生振动将石英管内器件取出,利用激光非接触切割原理,以石英管为中心设计光学旋转切割系统,实现360°旋转切割石英管,并分析试验数据,通过优化的试验数据,最终实现高效、无损伤的石英管切割技术。     

激光切割系统功率实时控制研究

激光功率对切割质量具有重要的影响,功率过大容易产生过烧现象.为了保证切割质量,研究了激光功率与切割速度的关系,基于可编程多轴运动控制器提出了激光功率实时控制的方法,使用开放性编写应用程序进行串口通信调整功率的方式实现激光功率的实时控制.采用这种方法进行激光切割试验,当激光功率能够随切割速度实时变化时,可以避免烧角现象.结果表明,此方法可以有效地提高切割质量,并且保证了激光切割的效率.     

紫外激光在半导体芯片切割中优势的研究

介绍了紫外激光切割技术的优越性，综述了紫外激光切割技术在半导体芯片切割中的应用．指出了传统砂轮切割技术在半导体芯片切割工艺的局限性，对各自的工作原理、特点、作了重点阐述。对传统砂轮切割技术和紫外激光切割技术进行了实验比较，并对紫外激光切割技术在半导体芯片切割工艺上的发展前景作了展望。     

车身覆盖件的三维激光切割转角过烧的研究

本文论述了三维激光切割技术在车身制造中的应用,探讨了三维激光切割中的难点。采用CO2激光在三维五轴数控切割机床上对车身覆盖件进行了切割工艺试验,对入射角和激光型式进行了深入的研究,并分析了对切割质量的影响。试验结果表明,入射角在临界角度内,对切缝宽度、切割面粗糙度和切割面波纹的影响不大,但超过这个临界角度,切割质量很差;在切割转角处时,应尽可能采用脉冲激光进行切割,避免转角处因热量过于集中而产生过烧,从而获得较好的切割质量。     

高速激光切割机床数控系统探究

随着经济的迅速发展,我国工业技术也有了较大的改善。现如今切割技术也有了很大的创新改进,新兴的激光切割,它目前已成为热切割技术发展的热点之一,激光切割技术相比较传统切割技术多了高精度、高效率、低污染等优点。为了满足激光切割装备的数字化、精密化等要求,实现此种技术的国产化。本文就高速激光切割机床数控系统各方面进行了研究分析,以此来满足我国对激光切割机床数控技术发展的要求。     

高速激光切割机床数控系统探究

随着经济的迅速发展,我国工业技术也有了较大的改善。现如今切割技术也有了很大的创新改进,新兴的激光切割,它目前已成为热切割技术发展的热点之一,激光切割技术相比较传统切割技术多了高精度、高效率、低污染等优点。为了满足激光切割装备的数字化、精密化等要求,实现此种技术的国产化。本文就高速激光切割机床数控系统各方面进行了研究分析,以此来满足我国对激光切割机床数控技术发展的要求。     

Multifocus Structures of Ultrashort Self-Focusing Laser Beam Observed in a Three-Photon Fluorescent Medium

Self-focusing effect and multifocus structures of an ultrashort (${sim}$160-fs) pulsed laser beam of ${sim}$ 1.3-$mu$ m wavelength are investigated in several organic liquids. The intensity-dependent self-focusing formation and multifocus structures of the infrared (IR) laser beam were directly observed in a three-photon active fluorescent dye solution cell, in which a high contrast image of the spatial structure of the self-focusing beam can be obtained due to the cubic dependence of the fluorescence intensity on the local IR laser intensity. By combining this dye solution cell with another cell filled with various transparent organic liquids, the contributions of these tested liquids to the observed self-focusing effect are elucidated. The numerical simulations for this type of self-focusing behavior are presented, based on the assumption that the major contribution to the observed self-focusing is the nonlinear refractive-index change of the solvent due to electronic-cloud distortion. The simulation results are in fairly good agreement with the experimental results.      

Transient and steady-state electrostrictive laser beam trapping

Electrostriction is a cause of laser beam self-trapping and damage in transparent glass. It predominates over other self-focusing mechanisms, such as Kerr effect or thermal self-focusing, under certain conditions. This paper shows that self-focusing can occur even if the laser pulse is so short that no steady state is achieved, provided the pulse power is large enough. In the steady state, the threshold power for self-focusing is independent of beam size. In the transient region, the threshold power increases and becomes proportional to the square of the initial beam radius, in the limit of large radius beams or short pulses. The theoretical trapping threshold derived here is less than typical experimental thresholds for track formation in glass.     

有限长激光脉冲在部分离化等离子体中的传播

为了研究有限长激光脉冲在部分离化等离子体中的传播特性,采用变分法推导出有限长激光脉冲在部分离化等离子体中的参量演化方程,分析了尾波场、相对论自聚焦和部分离化非线性极化强度的影响因素;通过分析焦斑半径和脉冲宽度满足的耦合方程,讨论了横向和纵向尾波场影响下的激光脉冲传播特性。结果表明,由于焦斑半径和脉冲宽度的耦合,激光脉冲在部分离化等离子体中传播必须满足一定条件;在部分离化等离子体中,考虑激光传播时脉冲宽度的变化是有必要的;对给定强度的激光脉冲,等离子体密度不变时,随着电离程度增大,尾波场会进一步增强激光脉冲的自聚焦,其中纵向尾波场比横向尾波场对激光脉冲的自聚焦作用更明显。这一结果对有限长激光脉冲电离诱导自注入及尾波场加速电子的方案具有理论指导意义。     

Electrostrictive self-focusing of picosecond laser pulse trains

A nanosecond-long train of picosecond laser pulses theoretically can produce self-focusing by electrostriction, even though the trapping threshold for a single picosecond pulse is very high. The relative roles of electrostriction and various types of Kerr effect in picosecond pulse train self-focusing should be assessed.     

Suppression of unwanted self-focusing effects in nonlinear optical experiments using liquid crystal

It is demonstrated that undesired self-focusing of strong laser beams through a liquid crystal film can be suppressed by the application of an alternating voltage on the sample. Diffraction efficiencies greater than 10% for optically induced optical phase gratings in the liquid crystal are obtained when self-focusing has been suppressed.     

高功率激光系统中的小尺度自聚焦研究

概述了高功率激光系统中小尺度自聚焦产生的机理及相应的评价标准和分析方法,重点对激光经过钕玻璃介质和频率转换晶体的小尺度自聚焦情况进行了分析和讨论,同时介绍了两种测量小尺度调制增长的方法。针对高功率激光系统,阐述了抑制小尺度自聚焦的几种方法,提出通过控制小尺度调制增量,减少高功率激光的非线性效应对光学元件损伤的方案。指出了聚变级高功率激光技术中非线性效应研究的发展趋势。     

产生自聚焦的机制的理论分析

本文利用Ｈｅｍｐｔｉｎｎｅ提出的光和物质相互作用的热力学模型以及不可逆热力学原理，讨论了强电磁波（激光）在各向同性介质中产生的非线性现象－自聚焦，结果发现，自聚焦产生于场的相干驱动扩散和耦合热效应（吸收介质）。另外考虑到物质扩散的耦合效应，得出温度梯度对相驱动扩散产生的自聚焦存在削弱的倾向。     

6A2--The influence of self-focusing on the stimulated Brillouin, Raman, and Rayleigh effects

In liquids with optically anisotropic molecules the largest nonlinear polarization, cubic in the field amplitudes, corresponds to the intensity dependent index of refraction. The resulting self-focusing of the laser beam is in turn responsible for the anomalous gain of the stimulated Raman emission. The stimulated Brillouin effect in these self-focusing fluids has the same threshold condition as the stimulated Raman effect. In both cases the condition is that self-focusing occurs within the cell length. The anomalous frequency broadening in these same liquids depends on the parameter(omega_{L} - omega'_{L})tau_{c}, where ωLandomega'_{L}are two frequencies occurring in the laser beam and τcis a correlation time for molecular reorientation. In agreement with this theory, more broadening was observed at higher temperatures, although the Raman gain has the opposite trend.     

Self-focusing during femtosecond micromachining of silicate glasses

Many recent investigations of micromachining with lasers, in vacuum and in ambient air environments, have demonstrated the improvements possible when using femtosecond-duration laser pulses compared with long laser pulses. There are obvious practical advantages for rapid micromachining in ambient air conditions. However, the maximum laser intensity and repetition rate are then eventually limited by the avalanche breakdown and nonlinear effects in the air through which the focused laser beam must propagate both outside the work piece and within the structure that is being machined. This paper investigates these limits in femtosecond deep hole drilling at high laser intensities in silicate glasses. In particular, it shows how nonlinear optical effects, particularly self-focusing, can dramatically affect hole shape and the rate of penetration during deep hole drilling. The experiments described here demonstrate how nonlinear Kerr focusing of femtosecond laser pulses occurs during propagation of intense femtosecond laser pulses through the atmosphere within the machined channel at powers levels significantly below the critical power for self-focusing in ambient air.     

Ultrafast solid-state mode-locked lasers using resonantnonlinearities

The authors discuss recent experiments in which resonant nonlinearities are used in order to directly mode lock solid-state lasers or to initiate self-focusing mode locking. Three configurations using resonant nonlinearities are considered. They are coupled cavity mode locking using a semiconductor nonlinear mirror, a further extension of this including self-focusing mode locking, and the closely related case of an intracavity saturable absorber dye. In the last two cases, the resonant nonlinearity only starts the self-focusing mode locking. Passive mode-locking techniques using resonant nonlinearities have the advantage that they self-start mode locking. The focus is on the Ti:sapphire laser, for which the techniques were first demonstrated