355 nm脉冲激光诱导等离子体开关削波

利用激光诱导等离子体开关技术,对355 nm脉冲激光自削波进行了实验和理论研究。分别采用5种不同焦距的透镜,集中讨论了透镜焦距及激光器输出单脉冲能量对脉宽压缩的影响,发现采用焦距为200 mm的透镜能够获得最佳的脉冲压缩效果。在聚焦透镜焦距200 mm,单脉冲能量160 mJ时,获得最短脉宽3.47 ns；在激光电离Cu小孔内壁表面及空气击穿共同作用下,获得了脉宽最短达2.11 ns的脉冲激光输出。此外,根据实验结果得到了355 nm激光空气击穿阈值,并与理论估算值进行比较,两者结果较为一致。

飞秒激光脉冲照射诱导含芴结构树脂共聚物结构变化及机理的研究

在室温下用聚焦的飞秒激光照射高折射率、低双折射的透明含芴结构树脂-对苯二甲酸乙二醇酯(PET)共聚物，探索飞秒激光制备高分子光学功能微结构的可能性。通过紫外-可见吸收光谱、红外光谱、电子自旋共振谱、光学显微镜、扫描电镜及透射电镜等分析手段，对该材料在飞秒激光照射后的结构变化及机理进行研究。结果发现：含芴结构树脂共聚物在飞秒激光照射后产生化学键断裂，生成未成对电子，并形成无定形碳；照射区在可见光区域的吸收增强；随激光能量密度的减少在激光会聚点附近诱导结构由慧尾状向单一细丝转变。演示了三维着色内雕。

A New theory for evaluating the number density of inclusions in films

A new formulation derived from thermal characters of inclusions and host films for estimating laser induced damage threshold has been deduced. This formulation is applicable for dielectric films when they are irradiated by laser beam with pulse width longer than tens picoseconds. This formulation can interpret the relationship between pulse-width and damage threshold energy density of laser pulse obtained experimentally. Using this formulation, we can analyze which kind of inclusion is the most harmful inclusion. Combining it with fractal distribution of inclusions, we have obtained an equation which describes relationship between number density of inclusions and damage probability. Using this equation, according to damage probability and corresponding laser energy density, we can evaluate the number density and distribution in size dimension of the most harmful inclusions. (c) 2005 Elsevier B.V. All rights reserved.

Statistical approach to bulk inclusion initialized damage in films

In experiments, we have found an abnormal relationship between probability of laser induced damage and number density of surface inclusion. From results of X-ray diffraction (XRD) and laser induced damage, we have drawn a conclusion that bulk inclusion plays a key role in damage process. Combining thermo-mechanical damage process and statistics of inclusion density distribution, we have deduced an equation which reflects the relationship between probability of laser induced damage, number density of inclusion, power density of laser pulse, and thickness of films. This model reveals that relationship between critical sizes of the dangerous inclusions (dangerous inclusions refer to the inclusions which can initialize film damage), embedded depth of inclusions, thermal diffusion length and tensile strength of films. This model develops the former work which is the statistics about surface inclusion. (c) 2006 Elsevier B.V. All rights reserved.

飞秒激光用多层介质膜脉宽压缩光栅的设计

以薄膜光学的干涉理论和衍射光学的傅里叶模式理论为基础，给出了0．8μm飞秒激光器用多层介质膜脉宽压缩光栅的理论设计；设计采用H3L（HL）^9H0．5L2．4H的多层介质膜为基底，当刻蚀后表面浮雕结构的占宽比为0．35，线密度为1480线／mm，槽深为0．2μm，顶层HfO2的剩余厚度为0．15μm时，对于Littrow角度（36．7°）和TE波模式入射的衍射光栅其-1级衍射效率达到95％以上．

钛宝石激光器中用优化Gires-Tournois镜产生15fs脉冲

根据飞秒脉冲锁模钛宝石激光器脉冲压缩的要求，介绍了负色散镜补偿色散的基本原理及其特点。详细阐述了优化Gires-Tournois(OG-T)镜的设计过程，并通过计算机优化得到理想设计膜系。采用离子束溅射的方法镀制了优化Gires—Tournois镜。测量了优化Gires-Tournois镜(编号为OGT#1)的透射率和群延迟色散，并与设计值进行了比较，分析了实测值产生偏差的原因，从而对镀膜参量进行了相应的调整，制造了第二批优化Gires—Tournois镜(编号为OGT#2)。将优化Gires—Tourn

薄膜体内缺陷对损伤概率的影响

由实验中得到的激光损伤概率与表面杂质密度的关系出发，结合XRD测试和激光损伤测试的结果，得到体缺陷或杂质破坏起主导作用的损伤机理．将激光作用时杂质吸收的热学和力学过程与杂质分布的统计规律结合起来，得到了深埋于薄膜内部的杂质诱导薄膜损伤概率与杂质密度、激光功率密度以及薄膜厚度的关系．该模型认为能诱导薄膜破坏的杂质尺寸范围与杂质填埋深度有关，所以不同深度处能诱导薄膜损伤的杂质密度不一样，理论结果与实验结果符合得很好．该理论模型还可以很好地解释损伤形貌．

Nd：YAG激光器光栅式扫描预处理的计算模拟与优化分析

采用计算模拟的方法．研究了光栅式扫描预处理的扫描方式以及脉冲能量波动、定位误差对预处理效率的影响。研究发现。脉冲能量波动及其定位误差使预处理效率降低，同时其影响与扫描方式之间存在相互调制作用．因此可以通过选择合适的扫描方式以及扫描间隔来优化预处理流程，提高预处理效率。此外发现，光斑呈等边三角形排列时的预处理效率优于正方形。

用于钕玻璃啁啾脉冲放大系统光谱整形的多层介质膜反射镜

在千焦拍瓦高功率啁啾脉冲放大系统设计中,为了尽量消除增益窄化和增益饱和效应的影响,同时尽可能提高高功率激光输出脉冲信噪比参数,激光脉冲时空和光谱的整形问题备受关注.提出一种光谱整形新方法,利用特定结构的多层介质膜反射镜,可实现对大能量高功率啁啾脉冲钕玻璃放大系统中啁啾脉冲的光谱整形.研究结果表明,只要合理选择多层介质膜系的结构参数,可有效地控制其反射率分布,且在保证反射相位基本不变的条件下其调制度可超过60%.针对钕玻璃1053nm波长设计而成的光谱整形反射镜,反射带宽可达到196nm,色分辨率约为0.1nm,在几十纳米波长范围所对应的相位偏差小于12mrad,相当于λ/524,能够满足"神光Ⅱ"千焦拍瓦改造的技术指标要求.

吸收杂质热辐射诱导光学薄膜破坏的热力机制

光学元件的破坏是限制高功率激光系统发展的主要问题,理解光学元件的破坏机制对于高功率激光系统的设计、运行参量选择以及器件技术发展有重要影响。以热辐射模型为基础研究了杂质吸收诱导光学薄膜破坏的热力过程。研究发现薄膜发生初始破坏所需时间很短,脉冲的大部分时间是引起薄膜发生更大的破坏。在考虑吸收杂质发生相变的情况下,计算了吸收杂质汽化对薄膜产生的蒸汽压力,论证了薄膜发生宏观破坏的可能性。此模型能很好地解释光学薄膜的平底坑破坏形貌。

Multi-exponentially photoelectric response of bacteriorhodopsin

A thin oriented bacteriorhodopsin (bR) him is deposited on a stainless steel slide by use of the electrophoretic sedimentation method. A junction is made with electrolyte gels having a counterelectrode to construct a bR-based photoelectric detector;. The photoelectric response signal to a 10 ns laser pulse is measured. A theory on the photoelectric kinetics of bR is developed based on the concept of the charge displacement current and the bR photocycle rate equations. Comparison between the theoretical and experimental results proves that the bR photoelectric response to a short laser pulse is a multi-exponential process. The decay time constants and amplitudes of each, exponential component are obtained by data fitting.

Characteristic of the ultrawideband electromagnetic radiation generated by PCSS

A novel ultra-wideband electromagnetic pulse generating method based on the photoconductive semiconductor switches (PCSS) is presented. Gallium arsenide is used to develop the PCSS for an ultrashort electromagnetic pulse source. The pulse generated by such PCSS is within picosecond (ps) time scale, and can yield power pulse with an voltage over 10 kV. The experimental results show that the pulses are stable, with the peak-peak amplitude change of 6% and the time jitter within several picoseconds. The radiations of the PCSS triggered by the picosecond laser and fenitosecond laser pulse series illustrate that the electromagnetic pulses would have high repetition of more than 80 MHz and frequency bandwidth of DC-6 GHz. The radiations of "lock-on " mode of the PCSS are also analyzed here. (c) 2007 Wiley Periodicals, Inc.

Spectrum broadening and reshaping via gain compensation of fiber amplifier

We report a novel technique to broaden and reshape the spectrum of picosecond laser pulse based on the seeder of gain switch laser diode and Yb(3+)-doped fiber amplifier (YDFA). From compensating the seed spectrum with the gain of YDFA, the seed pulse of 7 nm bandwidth is broadened to 20 nm, and the flat top spectral shape is obtained as well. A self-made fiber coupled tunable filter is used to realize the tunable output laser with the wavelength range from 1053 nm to 1073 nm and the line width of 1.4 nm.

ON THE DANGLING-BOND RELAXATION PROBLEM IN HYDROGENATED AMORPHOUS-SILICON

The influence of pulsed bias light excitation on the absorption in the defect region of undoped a-Si:H film has been investigated. Ac constant photocurrent method has been used to measure the absorption spectrum. The absorption in the defect region increases with the light pulse duration.The analysis of obtained results does not support the existence of a long time relaxation process of dangling-bond states in a-Si:H.