Dual-wavelength competitive output in Nd:Y3Sc1.5Al3.5O12 ceramic disk laser

In this paper, we demonstrated a dual-wavelength competitive output in Nd:Y3SC1.5Al3.5O12 ceramic disk laser. Different dual-wavelength output behaviors for Nd:YSAG and Nd:YAG ceramic disk laser were investigated and discussed. By applying the energy transfer model, we suggested the reasonable explanation for this new phenomenon as the disordered replacing of Al3+ ions by Sc3+ ions. The main advantage of the dual-wavelength ceramic laser is the possibility to serve as the seed source to generate Terahertz radiation. (C) 2008 Elsevier B.V. All rights reserved.

Passively Q-switched Yb : YAG laser with Cr4+: YAG as the saturable absorber

By using a continuous-wave Ti:sapphire laser as a pumping source, we demonstrated a passively Q-switched Yb:YAG laser at room temperature with Cr4+:YAG as the saturable absorber. We achieved an average output power of as much as 55 mW at 1.03 mum with a pulse width (FWHM) as short as 350 ns. The initial transmission of the Cr4+:YAG has an effect on the pulse duration (FWHM) and the repetition rate of the Yb:YAG passively Q-switched laser. The Yb:YAG crystal can be a most promising passively Q-switched laser crystal for compact, efficient, solid-state lasers. (C) 2001 Optical Society of America.

Laser-diode-pumped Cr4+,Nd3+: YAG with self-Q-switched laser output of 1.4 W

By use of a laser diode as a pump source, a self-Q-switched laser from a Cr,Nd:YAG crystal is demonstrated. The output Q-switched traces are very stable, the threshold pump power is 3.5 W, the pulse duration is 50 ns, and the slope efficiency is as high as 20%. In addition, the pulse width remains constant while the pulse repetition rate Varies with pump power. (C) 2000 Optical Society of America OCIS codes: 140.0140, 140.2020, 140.3380, 140.3480, 140.3540, 140.3580.

国产Yb∶YAG透明陶瓷实现激光输出

YAG单晶是高功率激光的重要材料，近年来高透明度多晶陶瓷作为激光介质引起人们广泛的注意。YAG陶瓷相对单晶具有易制造大尺寸、掺杂浓度高、易批量生产等优点。在Nd：YAG陶瓷获得长足发展的同时，Yb掺杂的陶瓷也得到了越来越多的关注。Yb：YAG陶瓷与Nd：YAG陶瓷相比具有许多优点：Yb掺杂的激光介质无交叉弛豫振荡和激发态吸收，有较宽的吸收带，较长的荧光寿命及较高的量子效率等。因此，高质量的Yb：YAG陶瓷将是非常理想的高功率激光材料。

单晶硅材料的1064nmNd：YAG脉冲激光损伤特性研究

作为微电子和光电子系统中普遍使用的一种结构材料，单晶硅一直是人们研究的焦点。长期以来，人们对其电学性质进行了非常深入细致的研究，却疏于对其抗击强激光辐照特性的研究。随着激光通讯和光电对抗技术的发展，对光学材料的激光破坏特性和加固技术进行研究的需求也显得越来越迫切。本文主要对单晶硅的抗激光损伤特性进行研究，研究了单晶硅材料在1064nmNd：YAG激光自由脉冲输出模式和单脉冲输出模式作用下的损伤特性，通过对两种激光作用下单晶硅损伤形貌的分析，在热效应与热力耦合模型的基础上，对单晶硅的激光损伤机制进行了探索。

Passively Q-switched mode-locking of diode-pumped Nd : YVO4 laser with GaAs intracavity absorber grown at low temperature

Using a low temperature grown GaAs wafer as an intracavity saturable absorber, a temporal envelope duration of 11 ns of Q- switched and mode- locked ( QML) 1064 nm operation was achieved in a very simple compact plane- concave cavity Nd: YVO4 laser, it was so short that the pulses can be used as Q- switching pulses. The maximal average output power is 808 mW with the repetition rate of 25 kHz, and the corresponding peak power and energy of a single Q- switched pulse was 2.94 kW and 32.3 mu J, respectively. The mode- locked pulse trains inside the Q- switched pulse envelope had a repetition rate of 800 MHz.

High-repetition rate Q-switched Nd : YVO4 laser with a composite semiconductor absorber

A diode-pumped Nd:YVO4 laser passively Q switched by a semiconductor absorber is demonstrated. The Q-switched operation of the laser has an average output power of 135 mW with a 1.6 W incident pump power. The minimum pulse width is measured to be about 8.3 ns with a repetition rate of 2 MHz. To our knowledge, this is the first demonstration of a solid-state laser passively Q-switched by such a composite semiconductor absorber. (c) 2006 Optical Society of America.

880 nm LD pumped passive mode-locked TEM00 Nd:YVO4 laser based on SESAM

We report on an 880 nm LD pumped passive mode-locked TEM00 Nd:YVO4 laser based on a semiconductor saturable absorber mirror (SESAM) for the first time. When the incident pump power was 16 W, 4.76 W average output power of continuous-wave mode-locked laser with an optical-to-optical conversion efficiency of 30% was achieved. The repetition rate of mode-locked pulse was 80 MHz with 25 ps pulse width. The maximum pulse energy and peak power were 60 nJ and 2.4 kW, respectively.

Application of enthalpy method for moving boundary problem in laser surface melting

A numerical analysis was carried out to study the moving boundary problem in the physical process of pulsed Nd-YAG laser surface melting prior to vaporization. The enthalpy method was applied to solve this two-phase axisymmetrical melting problem Computational results of temperature fields were obtained, which provide useful information to practical laser treatment processing. The validity of enthalpy method in solving such problems is presented.

脉冲激光合金化形成含非晶相表层的微观组织

利用Nd:YAG脉冲激光在不锈钢表层合金化SiO_2纳米颗粒，在熔池最表层14μm深度范围内形成Si合金化区域，Si含量呈非均匀分布特征。表层为非晶相与奥氏体的双相组织，非昌相约不散分布并呈现特殊的环状形貌，中心为非晶，外侧为纳米尺度的超细柱晶及等轴晶。分析了非晶形成机制。

Microstructure of Zr-alloyed coating using pulsed laser

Coatings were synthesized by laser alloying of zirconium (Zr) particles using a pulsed Nd:YAG laser on an austenite stainless steel. The distribution of Zr is uneven, in a depth of 18 mum just below the surface of the pool. The coating consisted of duplex microstructures, i.e. metallic glass (MG) and austenite. The MG formed in Zr-contained regions, with the Zr composition ranging from 7.6 to 16.8 at.%. The formation of the MG was attributed to an increase in glass-forming ability by Zr addition.

K418与42CrMo异种金属的激光穿透焊接

实验研究了连续波Nd：YAG激光焊接速度、侧吹保护气流量和离焦量等参量对激光穿透焊接K418和42CrMo焊缝成形的影响。结果表明，K418与42CrMo激光穿透焊接有X形和T形两种典型的焊缝形貌，且焊缝形貌是不对称的。随着焊接速度的提高，焊接线能量降低，焊缝尺寸变小，且焊缝上部尺寸变化比下部尺寸变化慢，焊缝形貌由X形过渡到T形。当离焦量在瑞利长度范围内时，焊缝正面宽度变化很小；当离焦量超出瑞利长度范围时，在足够高的激光功率密度下，焊缝正面宽度快速增加。在激光功率为3kW，侧吹保护气角度为35°条件下，通过优化焊接速度、侧吹保护气流量和离焦量等参量可以得到最佳焊缝质量。

Laser drilling improving circuit board manufacturing

We reported here a novel technique for laser high speed drillings on Printed Circuit Boards (PCBs). A CNC solid laser based system is developed to drill through and blind vias as an alternative to mechanical drilling. The system employs an Acousto-Optic Q-switched Nd: YAG laser, a computer control system and an X-Y moving table which can handle up to 400 x 400 mm PCB. With a special designed cavity the laser system works in a pulsed operation in order to generate pulses with width down to 0.5 mu s and maximum peak power over 10kW at 10k repetition rate. Delivered by an improved optical beam transforming system, the focused laser beam can drill hobs including blind vias on PCBs with diameter in the range of 0.1 - 0.4 mm and at up to 300 - 500 vias per second (depending on the construction of PCBs). By means of a CNC X-Y moving system, laser pulses with pulse-to-pulse superior repeatability can be fired at desired location on a PCBs with high accuracy. This alternative technology for drilling through or blind vias on PCBs or PWBs (printed wiring boards) will obviously enhance the capability to printed boards manufacturing.

脉冲激光离散加工熔池形态及其影响因素的研究

研究了Nd:YAG脉冲激光离散加工时功率密度和作用时间对熔池几何形态的影响，5CrMnMo 钢的实验结果表明：在本文所涉及的加工条件下，熔池存在热传导型和深熔型两种形态；激光作用时间小于4ms时，在相同作用时间下，随着激光功率密度的增加，熔池深宽比显著增加；但当作用时间大于4ms后，功率密度对深宽比的影响减弱，基于线性热传导模型的计算结果表明：熔凝起始阶段的固态加热过程可忽略；熔池几何尺寸在激光脉冲结束后某个时刻达到最大值；当平均功率密度大于5x10(5)W/cm(2),同时激光作用时间大于2ms时,热传导型激光熔池向深熔型激光熔池转变。

Numerical simulation of temperature field evolution of metallic alloy surface due to pulsed laser treatment

This paper performed a numerical simulation on temperature field evolution for the surface layer of a metallic alloy subjected to pulsed Nd:YAG laser treatment. The enthalpy method was adopted to solve the moving boundary problem, I.e. Stefan problem. Computational results were obtained to show the temperature field evolution. Effects of latent heat and mushy zone width on the temperature field were investigated. The results also show very high values of temperature gradient and cooling rate, which are typical characteristics during the solidification process.