贝塞尔光束与激光打孔

当高斯激光束用于打小孔时，焦深很小。截断的贝塞尔光束的主极大具有很长的焦深，可降低调焦精度，用于打小孔时优于高斯光束，但是分析表明两者的成孔质量和所能实现的深径比差不多。本文通过计算指出环状分布的光束经透镜后可在焦平面产生适用于激光打孔的贝塞尔－高斯光束，这是一种高效、简单实用的方法。     

非线性介质中会聚高功率激光的焦点位置控制

为了控制激光束的传输,使激光光束能根据实际情况在特定的位置聚焦,并且保证在传输过程中光束质量不退化,根据透镜聚焦和非线性介质的自聚焦理论,研究了高功率会聚激光光束在两者共同作用下焦点位置的变化.分析了各种因素对高功率激光光束的焦点位置的影响,并通过数值求解光束在非线性Kerr介质中所遵循的非线性薛定谔方程,得到焦点的位...     

非线性介质中会聚高功率激光的焦点位置控制

为了控制激光束的传输,使激光光束能根据实际情况在特定的位置聚焦,并且保证在传输过程中光束质量不退化,根据透镜聚焦和非线性介质的自聚焦理论,研究了高功率会聚激光光束在两者共同作用下焦点位置的变化.分析了各种因素对高功率激光光束的焦点位置的影响,并通过数值求解光束在非线性Kerr介质中所遵循的非线性薛定谔方程,得到焦点的位置变化和光束初始束宽,输入功率以及透镜焦距的关系,从而找到了控制焦点位置的方法.基于非线性薛定谔方程,对理论分析进行了相应的模拟验证,结果相互吻合.     

高能脉冲激光远场多参量测试系统设计

为研究高能脉冲激光远场光束质量,设计了一套激光远场多参量测试系统.首次将远场激光束的空间分布、脉冲波形和中心能量测试纳入到一个体系中.从总体设计、硬件构成、软件设计等三个方面对系统进行了阐述,重点介绍软件系统的实现过程.光束质量测试系统能够有效地获取远场激光的时空参数,为进一步进行远场激光性能评价奠定了基础.     

用远场法研究自由旋气动窗口的光学特性

 采用He-Ne激光,对穿过自由旋气动窗口的远场聚焦光斑进行图象采集和数据处理,研究本气动窗口对透过其输出通道的激光束所带来的偏转和随机抖动现象,计算分析气动窗口对激光束发散特性的影响,定义和实验研究气动窗口的光束质量β因子。同时,分析讨论气动窗口对激光束远场聚焦光斑光强分布的影响,并提出气动窗口光束质量和气动窗口设计的进一步研究思路。     

基于光学相干层析的激光焊接熔深监测方法

针对熔深间接测量方法测量精度低的问题,基于光学相干层析（OCT）的激光焊接熔深监测方法通过直接测量熔池小孔深度,实现在线质量监测。该方法基于低相干干涉精密测距原理,将测量光束与焊接光束同轴,具有测量精度高、抗干扰能力强的优点。搭建了基于谱域OCT(SD-OCT)的激光焊接熔深测量系统,在深熔焊条件下测量了熔池小孔深度,并应用百分位滤波算法从测量数据中提取出熔深曲线。针对百分位滤波算法的熔深提取精度受限于OCT测量数据噪声点和该算法需要根据焊接工况来调整滤波参数等问题,提出了一种基于局部离群因子（LOF）和最大值滤波的OCT熔深提取方法,通过与焊缝纵切面的熔深曲线对比发现,熔深提取精度最大提升了32%。实验结果表明,所提方法可有效提高熔深提取精度,且不需要调整算法滤波参数,适用性更强。     

预失真半导体激光列阵技术

相干半导体激光列阵体积小、重量轻,输出能量密度高,非常适于用作对光源尺寸要求苛刻的航天激光光源。为避免随航天器在轨运行的半导体列阵经受变化梯度剧烈的恒星、行星、空间低温热沉的交替加热和冷却的影响,以便能够正常工作,采用潜望式结构设计,将列阵置于舱内,列阵向航天器外输出激光必须经由舱外输出反射镜完成。然而,舱外输出反射镜受周围热环境影响和列阵输出激光束照射,会产生随机热变形,导致输出舱外的激光能量发散;并且,舱外输出反射镜面热变形导致镜面法向偏转,使得输出光束产生较大的指向偏转误差,这极大地降低了能够作用于目标之上的激光束的能量密度,严重恶化输出舱外的光束质量。通过理论推导结合ANSYS有限元分析软件和相关实验,在研究清楚相干半导体激光列阵作为航天激光源的构造、其光场与周围热环境共同作用于舱外输出反射镜的规律与特点后,给出了航天预失真半导体激光列阵激光源技术,通过回波法适时测量舱外输出反射镜引起的波前畸变,处理器配合D/A和高压放大器,驱动驱动器,使舱内添加的反射镜预失真成形,适时使列阵输出产生预失真波前畸变,以抵消舱外输出反射镜的热变形对输出舱外的激光束的影响。相关系统运行实验结果显示,此技术使半导体激光列阵能够适应宇航环境,向舱外输出保障质量的激光束。     

激光束在大气中长距离传输聚焦特性的研究

研究了大气湍流与热晕对于几种不同波长激光束的的长距离传输聚焦特性的影响。光束质量与光束漂值的理论与实验值基本一致。     

高功率激光的光学特性测试

由于激光核聚变研究工作的需要,促进了高功率钕玻璃激光器系统的发展。为了评价高功率钕玻璃激光器系统的光束质量,我们对某些激光的光学特性进行了测试,其中包括激光束近场的能量空间分布,激光束远场的特性和发散角,激光束波前的畸变和相干性,激光光谱等。文中的测试结果是在激光器件输出单脉冲功率水平为10~(10)W和10~(11)W的情况下进行的。     

激光加工技术中激光束的研究

从激光的特性出发,研究了激光光束及计算机控制系统在激光加工方面的缺陷,探讨了改进激光光束及设计软件的方案．     

非相干光纤组束激光的光束质量分析

为了提高非相干光纤组束激光的光束质量,对影响光束质量的诸参数进行了分析。理论分析和数值计算结果表明,离焦量ε、透镜焦距f、组束阵列宽度W以及由光栅引入的角偏移θ_B是影响组束激光光束质量的重要因素。提出了一种采用双光栅组束结构抑制角偏移θ_B的方法。该结构仅适用于远场发散角θ_0与θ_B量级相当的情况。     

一种大功率宽波段激光束散角的校准测试方法

在大功率激光系统的评价与分析中,激光器的光束品质是系统光束品质的决定性因素,也是激光器验收、鉴定的重要指标,其中束散角是判别激光光束质量的重要参数。本系统测试激光波长的范围比较宽,一般在0.532μm～10.6μm之间,没有合适的探测器能够覆盖整个波段,所以采用了一种新的方法来解决宽波段束散角的测量问题。选用CCD成像和扫描狭缝相结合的方法来实现宽波段激光光束束散角的测量,可见光和近红外波段（0.532μm～1.2μm）激光光束采用CCD法测量激光束散角,中红外波段（1.2μm～10.6μm）激光光束采用扫描狭缝法测量激光束散角。两种方法的结合可以较为精确地测量出不同波段的激光束散角。     

In-process high power CO2 laser beam position sensing

The case for in-process sensing is one of the strengths of laser materials processing, both in the variety of signals obtainable from the process and the range of techniques for beam guidance. It is known that beam/nozzle alignment is of importance for high quality laser cutting. Thus, an in-process beam position sensing system was devised in this study as one of the potential tools for automation of the cutting process. Further, if the beam could be stabilized at a given location automatically this would be equivalent to relocating the laser beam. Laser beam position sensing is the first step towards this goal. The aim of this study is to create a beam position sensing system. This work presents a new approach using a rotating slit, a focusing lens and a photodetector. An automatic alignment procedure is also investigated.     

Diagnostic system for two dimension intensity distribution of laser beam

The diagnostic system for two dimension(2-D)intensity distribution of laserbeam is a measuring instrument for many parameters of laser beam.2-D intensity distributionplot of laser beam is obtained by the two dimension scanning mirror which is controlled by amicrocomputer to scan the laser beam on a detector.Many parameters of laser beam such asthe isointensity distribution plot,the beam diameter,the beam waist diameter,the laser pow-er,the diverge angle and the beam brightness,are given by means of the microcomputer pro-cessing the data measured.Theoretical analysis of beam parameter transform is given.     

Parametric optimisation and microstructural analysis on high power Yb-fibre laser welding of Ti–6Al–4V

In this work thin sheets of Ti–6Al–4V were full penetration welded using a 5 kW fibre laser in order to evaluate the effectiveness of high power fibre laser as a welding processing tool for welding Ti–6Al–4V with the requirements of the aircraft industry and to determine the effect of welding parameters including laser power, welding speed and beam focal position on the weld microstructure, bead profile and weld quality. It involved establishing an understanding of the influence of welding parameters on microstructural change, welding defects, and the characteristics of heat affected zone (HAZ) and weld metal (WM) of fibre laser welded joints. The optimum range of welding parameters which produced welds without cracking and porosity were identified. The influence of the welding parameters on the weld joint heterogeneity was characterised by conducting detailed microstructural analysis.     

Characterization of laser ablation plasmas by laser beam deflection

Laser probe beam and multiple-pass deflection techniques were used for real time and in situ monitoring of laser ablation plasma plumes in the mTorr pressure regime. Intensity and transit time of shock wave fronts were studied as functions of focal lens position, laser energy and pressure. The velocity of the shock wave was determined to be up to 30 km s⁻¹ for a pressure of 40 mTorr and to drop below 4 km s⁻¹ at 1 Torr. For transparent targets rear-side shock wave velocity was on to be slower than the corresponding front one. This method promises a reliable diagnostic tool for pulsed laser deposition processing allowing an increase in the quality of coating technologies.     

大功率光纤激光焊焊缝跟踪偏差红外检测方法

精确控制激光束使其始终对准并跟踪焊缝是保证激光焊接质量的前提.针对大功率(激光功率10 kW)光纤激光焊接304型不锈钢紧密对接焊缝(间隙为0-0.1 mm),研究一种基于红外热像的焊缝跟踪偏差检测新方法. 采用红外传感高速摄像机摄取焊接区域熔池红外动态热像,分析激光束对准和偏离焊缝中心时的熔池温度分布和红外辐射特性,以熔池匙孔形变参数和热堆积效应参数作为激光束与焊缝中心偏差检测特征值,通过图像识别技术研究和分析特征值与焊缝偏差之间的关系. 激光焊接试验结果表明,熔池匙孔形变参数和热堆积效应参数与焊缝偏差 关键词： 大功率光纤激光焊 焊缝跟踪偏差 红外热像 检测     

Dual beam method for laser welding of galvanized steel: Experimentation and prospects

Laser welding of zinc-coated steel sheets in lap configuration poses a challenging problem, because of the zinc vapours spoiling the quality of the weld. In continuation to the earlier work, the novel solution of dual laser beam method for lap welding of galvanized steel sheets is discussed here in view of the recently obtained observations and ensuing concerns. In this method the precursor beam cuts a slot, thus making an exit path for the zinc vapours, while the second beam performs the needed welding. The metallurgical analysis of the welds is encouraging showing absence of zinc in the welded area. In the current work on this technique, new experimental results have been obtained verifying the earlier observations. Along with this, the possibility of using a transversely split-up beam for the welding purposes with this approach is discussed and analyzed in this paper. This new technique is expected to be very useful in prospective industrial applications requiring higher welding throughput along with the needed quality.     

CO2 laser beam modulating for surface texturing machining

Laser texturing is a novel technique that may be used to texture a cold roller in the process of manufacturing high quality steel sheets. With the aim of improving the quality of the textured roller by using a CO₂ laser, a new laser beam modulating device is proposed. An optical beam expander with a fast rotating chopper system is designed. The laser pulse is split into two parts by the chopper blades; one is the preheating pulse that is reflected onto optical loop mirrors; the other is the directly transmitted pulse that creates the craters at the preheated spots. The preheating beam focus spot size and position can be adjusted. The focusing characteristics and optical parameter compensation for the flying optics are investigated. The heat transfer and melt process of laser texturing are numerically simulated. The effects of the double pulses on the texturing are analyzed. The effect of preheating the sample ahead of the laser texturing pulse is examined. The surface profile and bump hardness show improvements by using this approach.     

Relationship between weld quality and optical emissions in underwater Nd: YAG laser welding

In underwater laser welding (LBW), the weld quality is very dependent on the shielding conditions of the local dry cavity when other welding parameters are fixed. Thus, diagnosing the stability of the local dry cavity is the key to monitoring of underwater LBW. In this work, a sensing system containing two optical sensors was set up to detect the infrared and ultraviolet waveband of the optical emissions induced in the welding. The effect of water on the laser welding was studied first by conducting direct underwater welding, which was performed without any method to exclude the water from the welding zone. A kind of plasma that has strong ultraviolet emission formed if the water depth was more than several millimeters, which considerably reduced the penetration depth. Then a gas-shielding nozzle was used to form a local dry cavity for underwater LBW. The relationship between the optical signals and the weld quality with various shielding conditions were investigated. The results show that the detected signal well reflects the shielding condition variations of the local dry cavity. The optimal shielding condition could be determined by signal stability.