YVO4-Nd:YVO4复合晶体热效应研究

在全固态激光器中使用了复合结构的激光晶体,通过端面泵浦复合晶体工作特点分析,提出了矩形截面复合晶体热分析模型。在热模型中,考虑了复合晶体具有轴向加热、周边恒温,耦合后的泵浦光束具有高斯分布的特点。利用热传导方程,得出了YVO₄-Nd:YVO₄复合晶体内部温度场及端面热形变的一般解析表达式。研究结果表明,若用输出功率为20 W的激光二极管端面泵浦YVO₄-Nd:YVO₄复合晶体(其中复合晶体中YVO₄晶体长为2 mm,Nd:YVO₄晶体长为6 mm,钕离子掺杂质量分数为0.5%),泵浦光斑为0.2 mm时,复合晶体内最大温升为324.5 ℃,泵浦端面具有3.61 mm的热形变量。在相同泵浦条件下,采用复合晶体替代Nd:YVO₄晶体,可将其最大温升降低23.4%,这对于消弱激光晶体热效应的影响,解决激光二极管端面泵浦激光晶体引起的非均匀温升以及热折裂问题,提高激光器性能有着重要的意义。     

Initial operation of a pulse-burst laser system for high-repetition-rate Thomson scattering

A pulse-burst laser has been installed for Thomson scattering measurements on the Madison Symmetric Torus reversed-field pinch. The laser design is a master-oscillator power-amplifier. The master oscillator is a commercial Nd:YVO(4) laser (1064 nm) which is capable of Q-switching at frequencies between 5 and 250 kHz. Four Nd:YAG (yttrium aluminum garnet) amplifier stages are in place to amplify the Nd:YVO(4) emission. Single pulses through the Nd:YAG amplifier stages gives energies up to 1.5 J and the gain for each stage has been measured. Repetitive pulsing at 10 kHz has also been performed for 2 ms bursts, giving average pulse energies of 0.53 J with ΔE/E of 4.6%, where ΔE is the standard deviation between pulses. The next step will be to add one of two Nd:glass (silicate) amplifier stages to produce final pulse energies of 1-2 J for bursts up to 250 kHz.     

1.1 W内腔和频连续波橙黄光Nd:YVO4激光器

研制了一种由激光二极管阵列端面泵浦的Nd:YVO4晶体腔内双波长和频连续波大功率橙黄光激光器.利用I类临界相位匹配LBO,由1 064 nm和1 342 nm内腔和频获得了593 nm橙黄激光.在12 W注入泵浦功率下,获得了1.1 W的TEM00模和低噪声橙黄激光输出,光光转换效率为9.2%,M2因子＜1.2,4 h功率不稳定度＜±2%.该输出功率是目前腔内和频593 nmNd:YVO4激光器中最高的.     

6.5W LD泵浦914 nm钒酸钇激光器

掺钕钒酸钇作为一种重要的激光增益介质,以其受激发射截面大、对809 nm波长存在很强的宽吸收带、偏振发射等优点,在LD端面泵浦全固态激光器中得到了广泛的应用,其中比较有应用价值的受激发射谱线为1 064 nm,1 342 nm和914 nm。由于914 nm谱线属准三能级结构,以及钒酸钇晶体较低的热导率,限制了其向大功率方向的发展。研究了一种具有较高效率的大功率钒酸钇连续输出激光器,通过采用简单的折叠腔设计和对腔镜镀适当的介质膜,抑制了波长为1 064 nm和1 342 nm的高增益谱线。当泵浦功率为29W时,输出功率高达6.5W,斜效率为37.9%,光光转换效率为22.4%.     

量子阱二极管泵浦的Nd:YVO4/Cr:YAG高重复率被动调Q激光器

量子阱二极管端面泵浦的Nd:YVO₄激光器中,采用Cr:YAG作为可饱和吸收体,获得了1.06μm的高重复率被动调Q脉冲激光输出.在吸收泵浦功率528.3mW时,输出脉冲能量0.19μJ,宽度32ns,脉冲重复率达158.7kHz.     

激光分布对抽运Nd:YVO4晶体热效应的影响

以解析各向异性分析理论为基础,研究矩形横截面Nd:YVO4激光晶体受到超高斯分布LD端面抽运时,激光晶体温度场分布和晶体抽运面热形变分布。通过激光晶体工作特点分析,考虑了激光分布和激光光束半径变化,建立了符合激光晶体工作状态的热模型。利用各向异性介质热传导方程的一种新求解方法,得出了矩形截面Nd:YVO4晶体的温度场、端面热形变场的通解表达式。研究结果表明：当使用输出功率为15W半导体激光器（超高斯阶次为1）端面中心入射Nd:YVO4晶体（晶体掺钕离子质量分数为0.5%）时,在抽运端面中心获得243.8C最高温升和1.99m最大热形变量,与实验结果一致。这种方法可以应用到其它激光晶体热问题研究中,为有效解决激光系统热问题提供了理论依据。     

端面泵浦热传导各向异性激光棒温场特性研究

了解决LD端面泵浦热传导各向异性激光介质产生的热效应问题,建立了端面绝热、侧面冷却的Nd:YVO4晶体热模型。考虑到Nd:YVO4为热传导各向异性材料,而光纤耦合LD输出光束有着超高斯分布的特点,利用特征函数法和常数变异法得到了超高斯光束端面泵浦热传导各向异性激光介质温度场的一般解析表达式。并定量分析了超高斯泵浦光阶次、泵浦功率以及光斑尺寸对于Nd:YVO4晶体温度场的影响。新的各向异性介质热传导方程求解方法具有计算量小、精度高等特点。研究结果表明：若LD输出功率为30W,光学聚焦耦合器的传输效率为82%时,4阶超高斯光束端面泵浦掺钕离子质量分数为0.5%的Nd:YVO4晶体,泵浦面获得528.95C的最大温升。所得结果可用于LD端面泵浦热传导各向异性激光介质全固态激光器热稳腔的设计之中,对于提高激光器性能具有了理论指导作用。     

全固态355 nm连续紫外激光器的优化设计

通过优化腔型设计, 实现了LD端面抽运Nd:YVO₄腔内三次谐波转换全固态连续355 nm紫外激光器高效率输出。选用平-凹腔结构并考虑到Nd:YVO₄晶体的热透镜效应、模式匹配、倍频晶体位相匹配等因素对输出功率的影响,对谐振腔长进行了详细的分析计算。在激光谐振腔内, 1 064 nm的基频波经KTP晶体倍频产生532 nm激光,二者再经LBO晶体和频获得了355 nm紫外激光。当LD抽运功率为3 W时,355 nm连续紫外激光输出功率达6.4 mW。与折叠腔进行比较,发现在小功率抽运情况下,直腔结构紧凑、易于调节、输出功率较大。     

LD泵浦Nd:YVO4激光器的测距应用

将ＬＤ泵浦的Ｎｄ：ＹＶＯ４激光与连续波频率调制技术相结合、提出一种绝对距离测量新方案。小尺寸的Ｒｄ：ＹＶＯ４晶体提高了光源的时间相干性,这一点对于长距离测量有重要意义。通过引入补偿通道,消除ＰＺＴ非线性调制的影响。实验结果证明了该方案的可行性。     

外腔型YVO4拉曼激光器

采用提拉法生长了高光学质量的YVO4晶体,最大尺寸为28mm×40mm,重126g。以脉冲宽度为40皮秒的Nd:YAG锁模激光器作为激发源,研究了YVO4晶体在外置谐振腔条件下的拉曼输出特性：多波长输出的总转换效率达到51.4%,最大输出能量2.21mJ;1175nm一级斯托克斯拉曼输出的最高转换效率为32%,最大输出能量0.57mJ;1313nm二级斯托克斯拉曼输出的最高转换效率为12.3%,最大输出能量0.36mJ。     

LD泵浦固体激光器驱动倍频输出系统调制噪声的研究

阐述了一具体实验现象 :LD泵浦掺钕矾酸钇固体激光器输出激光再驱动 ( KTP)倍频晶体产生倍频绿激光输出的系统 ,存在严重噪声 ,但可通过改变入射角 ,用对应的特定频率调制 ,使噪声降至很小     

长脉宽脉冲激光硅片弯曲成形试验

利用毫秒脉宽Nd:YAG激光对硅片进行了弯曲试验,给出了长脉宽脉冲激光弯曲硅片的能量阈值条件。研究了长脉宽Nd:YAG激光脉冲频率和脉冲宽度参数对硅片弯曲角度的影响,同时说明了脉冲频率和脉冲宽度参数对弯曲角度的影响可以转换成扫描速度和功率密度对弯曲角度的影响,并对试验结果进行了分析,引入了脉冲占空比来表征能量的时域分布对弯曲现象的影响。试验结果表明,采用毫秒量级脉冲激光可以对硅片进行弯曲加工,弯曲角度可达20°以上。     

三镜直腔结构MgO∶PPLN高效连续光参量振荡器

为了优化MgO:PPLN连续光参量振荡器(OPO)的输出特性,对三镜直腔结构的内腔式OPO系统进行腔结构设计,对其同时输出高效的信号光和闲频光进行研究。采用半导体激光端面抽运Nd:YVO4晶体实现连续的1064 nm激光为基频光。对比分析了基频激光腔和OPO腔各腔镜分别采用平面镜或平凹镜的三种腔型结构的激光输出特性。基于30.5 μm的极化周期和12.4 W入射抽运功率时,获得了最高输出功率3.92 W（信号光2.6 W和闲频光1.32 W）,转化效率31.6%的激光输出,对应的信号光和闲频光的中心波长分别为1549 nm和3394 nm。结果表明三个腔镜均采用平凹镜时,可有效的压缩基频激光腔在MgO:PPLN晶体上的光斑,提升基频激光的功率密度,而且基频激光腔和OPO腔的基模光斑在MgO:PPLN晶体上更好的匹配,从而提升变频效率。     

高平均功率腔内和频蓝光Nd:YAG激光器

高平均功率蓝光激光是当前固体激光技术研究热点之一。尽管通过Nd³⁺的⁴F_3/2→⁴I_9/2态谱线倍频可获得瓦级蓝光输出,然而其准三能级物理特性严重限制其更高功率输出。研究了Nd³⁺离子⁴F_3/2→⁴I_13/2态1.3 μm谱线腔内三倍频产生高平均功率蓝光激光,获得4.3 W蓝光激光输出,重复频率3.5 kHz,脉冲宽度150±10 ns,光束质量M²因子约为5±1。研究表明:Nd∶YAG晶体1.3 μm多谱线振荡是制约实验结果的重要因素,若克服多谱线振荡问题,有望获得10 W级蓝光激光输出。     

A two-wave 1064/532-nm diode-pumped pulse-periodic YAG:Nd laser

A compact 1064/532-nm diode-pumped pulse-periodic YAG:Nd laser is described. Its parameters are as follows: the wavelength is 1064 nm, the pulse energy is 1.2 J, the pulse duration is 5 ns, the pulse repetition rate is 100 Hz, and the beam divergence is ≤1.6 mrad. The laser light efficiency is 12%, and the full efficiency of the laser system is 4%. Two lasing modes are realized in the laser: at the fundamental frequency and with the frequency conversion into the second harmonic at a wavelength of 532 nm and a pulse energy of 0.3 J.     

LD泵浦腔内倍频Nd:YAG/LBO蓝光473nm激光器的低噪声运转

激光二极管（LD）泵浦腔内倍频Nd:YAG/LBO蓝光473nm激光器在不加入腔内特殊元件的情况下,往往倍频输出功率具有很大的高频噪声,即所谓的“蓝光问题”！这大大限制了473nm蓝色激光的应用！为了降低该激光器件倍频输出功率的高频噪声,采用了通过提高腔内基频光循环强度和缩短激光晶体以减小准三能级激光系统再吸收损耗的方法来实现473nm激光器的低噪声运转！实验中利用两个2W激光二极管耦合作为泵浦源及1.0mm厚的Nd:YAG材料作为激光晶体,在利用10mm长LBO材料作为倍频晶体的情况下,获得了输出功率为195mW的具有低噪声特性的473nm蓝光激光运转！实验结果表明：倍频输出功率（峰－峰值）/平均值小于1%！激光输出在1h内没有发生激光跳变现象发生并且无需腔内其它元件的引入。     

Effects of Operating Parameters on the Static Properties ofPulsed Laser Welded Zinc-Coated Steel.

The paper presents an analysis of the influences of the dominant parameters of the pulsed Nd:YAG laser seam welding process on the static behaviour of the welds. These parameters include average peak power density (APPD), mean laser power, traverse speeds, pulse duration, and pulse shapes. Three typical temporal pulse types – ramp-up, ramp-down, and "rectangu-lar" power pulses were used in this study. Laser seam welds were produced in 0.7 mm thick electrogalvanised steel sheets. A number of destructive tests of pulsed Nd:YAG laser welded zinc-coated steel sheet have been carried out to characterise the static properties of welds including hardness, bending strength, and ductility. An experimental study of acceptable welds revealed that the hardness was affected only by the traverse speed. The bend strength was increased with decreas-ing travel speed and increasing pulsed laser parameters. It was found that the operating parameters have no effect on the tensile strengths of the welds.     

Predictive model and process parameters optimization of Nd:YAG laser micro-turning of ceramics

The present work highlights laser micro-turning operation of 10-mm diameter cylindrical-shaped alumina (Al₂O₃) ceramic using pulsed Nd:YAG laser. The paper also addresses development of mathematical models for correlating the various micro-machining parameters such as laser beam average power, pulse frequency, workpiece rotational speed, assist air pressure, and Y feed rate with the response criteria such as surface roughness and deviation in turned depth for achieving desired surface quality as well as dimensional accuracy during micro-turning operation using Nd:YAG laser system. Response surface methodology-based design of experiments has been adopted for the experimentation. This investigation also highlights the various test results that confirm the validity and correctiveness of the developed mathematical models through analysis of variance test. The test results were analyzed through various response surface plots to study the effect of the process parameters on the aforementioned responses. The results of validation experimentation show a good agreement for the developed empirical models. Sensitivity analyses of the developed models have been done to find out the variation in the output with respect to variations in the significant input process parameters. Moreover, multi-performance optimization has been done to find out the optimal parametric setting for achieving the desired process performances. Analysis also has been made based on scanning electron microscopy micrographs of the laser micro-turned surface achieved during machining at multi-criteria optimization setting.     

Characterization of hole circularity in pulsed Nd:YAG laser micro-drilling of TiN–Al2O3 composites

In micro-manufacturing, circularity of a drilled hole at entry and exit are important attributes which greatly influence the quality of a drilled hole. This study investigates the effect of five parameters in the circularity of drilled holes in pulsed Nd:YAG laser micro-drilling process. The drilling operation has been carried out on titanium nitride–alumina (TiN–Al₂O₃) composite, an important electroconductive ceramics suitable for wear and heating applications. The effect of various process parameters like lamp current, pulse frequency, pulse width, air pressure, and focal length of Nd:YAG laser micro-drilling on hole circularity at entry and exit has been investigated through response-surface-methodology-based experimental study. The parametric combination for optimal hole circularity at entry and exit has also been evaluated.     

Enhanced processing speed in laser drilling of stainless steel by spatially and temporally superposed pulsed Nd:YAG laser radiation

Percussion drilling through holes in stainless steel (1.4301, 5, 8, and 10 mm in thickness) was performed with the superposed radiation of two pulsed Nd:YAG lasers. Holes were drilled with flash lamp pumped Nd:YAG slab-laser radiation with a pulse duration of 0.5 ms superposed with diode-pumped solid-state (DPSS) laser radiation with a pulse duration of 17 ns. The drilling efficiency is improved by the spatially and temporally superposed radiation of the two lasers. With the superposed laser radiation, drilling through stainless-steel samples at a maximum aspect ratio of 60 is performed up to four times faster with the reproducibility of the drilling time improved by a factor of six in standard deviation.