纳秒级脉冲激光自动跟踪积分式测量方法

介绍了一种纳秒级脉冲激光光斑能量分布测量电路的设计方法,采用自动跟踪积分方式,根据预测先将脉冲光电流积分并保存,然后用速度较低的A/D芯片进行A/D转换,该方法避免了采用高速A/D芯片,且可以获得较高的采样分辨率,特别是在需要采集的通道数较多时具有明显优势。     

用自积分式罗氏线圈测量纳秒级高压脉冲电流

介绍了测量纳秒级高压脉冲大电流信号用的自积分式罗氏线圈的优点、用途、基本原理及设计。利用传输理论分析了它的信号响应及干扰。对研制出的罗氏线圈进行了标定。设计的线圈的灵敏度在1.4mV/A,可以采用的上升时间小于2ns,脉宽小于200ns,电流信号10A～40kA。自积分式罗氏线圈广泛用于脉冲功率技术中的快过程大电流测量。     

用自积分式罗氏线圈测量纳秒级高压脉冲电流

 介绍了测量纳秒级高压脉冲大电流信号用的自积分式罗氏线圈的优点、用途、基本原理及设计。利用传输理论分析了它的信号响应及干扰。对研制出的罗氏线圈进行了标定。设计的线圈的灵敏度在1.4mV/A，可以采用的上升时间小于2ns，脉宽小于200ns，电流信号10A～40kA。自积分式罗氏线圈广泛用于脉冲功率技术中的快过程大电流测量。     

GW级纳秒脉冲源激光触发同步实验

结合GW级纳秒脉冲源建立了实验平台,研究了激光触发开关的延迟时间及其抖动与激光能量、工作电压、激光波长、透镜焦距等参数的关系。结果表明:开关延迟与抖动随激光脉冲能量的上升、工作电压的上升而逐渐减小;采用紫外光得到的开关延迟与抖动小于相同条件下红外光得到的结果;在高气压小间隙开关条件下,采用小的透镜焦距可以得到更小的开关延迟与抖动。开关在自击穿电压220 kV、欠压比为80%、采用7 mJ,266 nm 波长激光时的抖动为0.3 ns,在此条件下进行了两台脉冲源的同步实验,得到其同步偏差85%置信率小于0.3 ns。     

GW级纳秒脉冲源激光触发同步实验

结合GW级纳秒脉冲源建立了实验平台,研究了激光触发开关的延迟时间及其抖动与激光能量、工作电压、激光波长、透镜焦距等参数的关系。结果表明：开关延迟与抖动随激光脉冲能量的上升、工作电压的上升而逐渐减小;采用紫外光得到的开关延迟与抖动小于相同条件下红外光得到的结果;在高气压小间隙开关条件下,采用小的透镜焦距可以得到更小的开关延迟与抖动。开关在自击穿电压220 kV、欠压比为80%、采用7 mJ,266 nm 波长激光时的抖动为0.3 ns,在此条件下进行了两台脉冲源的同步实验,得到其同步偏差85%置信率小于0.3 ns。     

积分球技术在高能激光能量测量中的应用

介绍了一种采用积分球技术对高能激光能量测试的有效方法,给出了其工作原理、设计要求和误差分析.     

等离子体削波纳秒激光脉冲波形测量

实验上采用比对方法测试了激光不经过固体与经过固体介质产生等离子体削波的脉冲波形信号,获得等离子体削波效应产生的脉冲削波倍数。实验结果表明,在波长1.064 m,脉宽1 ns,聚焦透镜焦距100 mm,薄石英片厚度100 m,约束等离子体的小孔直径80 m情况下,等离子体效应产生的脉冲削波倍数为12~14;分别改变石英片厚度和约束等离子体小孔直径,等离子体脉冲削波倍数不变;增加入射激光能量,脉冲削波倍数增加,且经过等离子体后的激光脉冲波形的后沿逐渐出现很陡的下降沿。在产生脉冲削波的截断点位置进行图形拼接重构得到激光脉冲波形信息。     

等离子体削波纳秒激光脉冲波形测量

实验上采用比对方法测试了激光不经过固体与经过固体介质产生等离子体削波的脉冲波形信号,获得等离子体削波效应产生的脉冲削波倍数。实验结果表明,在波长1.064 m,脉宽1 ns,聚焦透镜焦距100 mm,薄石英片厚度100 m,约束等离子体的小孔直径80 m情况下,等离子体效应产生的脉冲削波倍数为12~14;分别改变石英片厚度和约束等离子体小孔直径,等离子体脉冲削波倍数不变;增加入射激光能量,脉冲削波倍数增加,且经过等离子体后的激光脉冲波形的后沿逐渐出现很陡的下降沿。在产生脉冲削波的截断点位置进行图形拼接重构得到激光脉冲波形信息。     

纳秒激光脉冲诱导硅表面微结构

利用Nd:YAG纳秒激光脉冲,在能量密度为1～10 J/cm2范围内辐照单晶硅,形成了表面锥形微结构,在SF6气氛和空气环境下均形成了锥形尖峰表面微结构。SF6气氛下产生的锥形尖峰顶端都有小球,部分锥形上还有二次尖峰形成,空气中纳秒激光诱导的锥形尖峰微结构顶端和边缘有由液滴固化形成的粒状物质,不同于利用准分子纳秒激光诱导的细长须状结构和飞秒激光辐照下产生的具有表面枝蔓状纳米结构的锥形微结构。实验结果表明,这种尖峰微结构的形成与辐照激光的波长和脉冲持续时间有关。对空气中微构造硅的辐射反射的初步研究表明,在500～2 400 nm范围内的光辐射反射率不高于20%。     

纳秒激光脉冲诱导硅表面微结构

利用Nd:YAG纳秒激光脉冲,在能量密度为1~10 J/cm2范围内辐照单晶硅,形成了表面锥形微结构,在SF6气氛和空气环境下均形成了锥形尖峰表面微结构。SF6气氛下产生的锥形尖峰顶端都有小球,部分锥形上还有二次尖峰形成,空气中纳秒激光诱导的锥形尖峰微结构顶端和边缘有由液滴固化形成的粒状物质,不同于利用准分子纳秒激光诱导的细长须状结构和飞秒激光辐照下产生的具有表面枝蔓状纳米结构的锥形微结构。实验结果表明,这种尖峰微结构的形成与辐照激光的波长和脉冲持续时间有关。对空气中微构造硅的辐射反射的初步研究表明,在500~2 400 nm范围内的光辐射反射率不高于20 %。     

Dynamics of laser hole drilling with nanosecond periodically pulsed laser

Results are presented on the dynamics of the laser drilling process for a single hole using a periodically pulsed nanosecond laser with a repetition rate up to 60 kHz. The intensity dependence of drilling velocity was determined by measuring the delay time between the beginning of exposure and the moment when the hole opens. The hole collapse phenomenon was observed in our experiments. The competition process between material ejection and the flow of the liquid phase into the ejected area is supposed to be responsible for the hole collapse.     

Semiconductor disk laser in the nanosecond lasing mode

Pulse generation (pulse duration 370 to 34 ns) is obtained for the semiconductor disk laser optically pumped by the Cr:LiCAF laser beam. Dynamics of its lasing spectrum during the pump pulse is investigated. Generation pulse variations under the mismatch of the pump spot and the region of the main disk lasing mode are studied.     

High-sensitive terahertz detection by parametric up-conversion using nanosecond pulsed laser

A high-sensitive terahertz detector operating at room temperature was demonstrated based on parametric upconversion.A nanosecond 1064-nm Nd:YAG laser was used to pump the parametric up-conversion detector and the upconversion from terahertz wave to NIR laser was realized in a lithium niobate crystal.The minimum detectable terahertz energy of 9 p J was realized with the detection dynamic range of 54 d B,which was three orders of magnitude higher than that of commercial Golay cell.The detectable terahertz frequency range of the detection system was 0.90 Thz–1.83 THz.Besides,the effects of pump energy and effective gain length on the detection sensitivity were studied in experiment.The results showed that higher pump energy and longer effective gain length are helpful for improving the detection sensitivity of parametric up-conversion detector.     

Optical properties of silicon microcolumn grown by nanosecond pulsed laser irradiation

We have investigated the optical properties of silicon pillars formed by cumulative nanosecond pulsed excimer laser irradiation of single-crystal silicon in vacuum created under different repetition rates. The changes in optical characteristics of silicon pillar were systematically determined and compared as the number of KrF laser shots was increased from 1 to 15,000.The results show that silicon pillar PL curves exhibit a blue band around 430 nm and an ultraviolet band peaking at 370 nm with the vanishing of the green emission at 530 nm. A correlation between the intensity of the blue PL band and the intensity of the Si-O absorption bands has been exploited to explain such emission, whereas, the origin of the ultraviolet band may be attributed to different types of defects in silicon oxide.     

Submicron foaming in gelatine by nanosecond and femtosecond pulsed laser irradiation

We compare the foaming characteristics induced by irradiation with single ns and fs laser pulses of UV, VIS and IR wavelengths on gelatines differing in gel strength (bloom values 75 and 225) and in crosslinking degree. We have observed that while laser irradiation with nanoseconds leads to the formation of a microfoam layer at 266 nm, and melting and crater formation at longer wavelengths (532 and 1064 nm), fs pulse irradiation leads to submicron foaming at all wavelengths studied (266, 400 and 800 nm). These results show the possibility of controlling the submicrometric foam structure in this biomaterial and can shed light into the working mechanisms of fs laser nanoprocessing in biomaterials, where increase of temperature, thermoelastic stress generation, and stress-induced bubble formation are mediated by the generated plasma.     

Numerical simulation of nanosecond pulsed laser welding of eutectoid steel components

This paper considers the micro-closed seam laser welding of two nearly eutectoid carbon steel grades. These materials are difficult to weld due to their poor ductility. In particular, in closed seam welding, the laser beam starts and finishes in the same point thus increasing the risk of cracks. A numerical simulation of micro-welding of nearly eutectoid steels by nanosecond pulsed laser is carried out to evaluate the weld pool dimension and the heat-affected zone extension. Optimized welding parameters and strategy are determined by means of simulation and they are successfully applied in the welding of a 1.0%C shaft and a 0.7%C gear.     

Ionization effect to plasma expansion study during nanosecond pulsed laser deposition

The dynamic characteristic and effects of plasma play an important role in film growth process of pulsed laser deposition (PLD). Based on numerical hydrodynamic modeling, supposed the laser radiation and partial ionization of the plasma as a dynamic source, we deduce a set of new plasma expansion dynamics equations. Based on which, as an example of carbon target, using finite difference method, the plasma flow dynamics evolvement in vacuum is investigated. Our results show the dynamic partial ionization increases the expansion in all directions, which changes into a new dynamic source for plasma expansion. In the axial direction, because of the collisional interactions between particles, the plume density peak is in the vicinity of the target surface and the acceleration of plasma occurs mainly near the target surface too. In the transverse direction, the plume peak is not near the target, but at the surface. The space expansion distance is far less than the axial direction because there is no high initial velocity component in this direction. The predictions of the plasma expansion action based on the proposed dynamics source assumption are found to be in agreement with the experimental observation.