Influence of oxygen post-treatment on laser-induced damage of antireflection coatings prepared by electron-beam evaporation and ion beam assisted deposition

Antireflection coatings at the center wavelength of 1053 nm were prepared on BK7 glasses by electron-beam evaporation deposition (EBD) and ion beam assisted deposition (IBAD). Parts of the two kinds of samples were post-treated with oxygen plasma at the environment temperature after deposition. Absorption at 1064 nm was characterized based on surface thermal lensing (STL) technique. The laser-induced damage threshold (LIDT) was measured by a 1064-nm Nd:YAG laser with a pulse width of 38 ps. Leica-DMRXE Microscope was applied to gain damage morphologies of samples. The results revealed that oxygen post-treatment could lower the absorption and increase the damage thresholds for both kinds of as-grown samples. However, the improving effects are not the same. (c) 2008 Elsevier B.V. All rights reserved.

Investigation of annealing effects on the laser-induced damage threshold of amorphous Ta2O5 films

Ta2O5 films were deposited using the conventional electron beam evaporation method and then annealed at temperatures in the range 373-673 K. Chemical composition, scattering and absorption were examined by X-ray photoelectron spectroscopy (XPS), total integrated scattering (TIS) measurement and the surface thermal lensing (m) technique, respectively. The laser-induced damage threshold (LIDT) was assessed using the output from an Nd:YAG laser with a pulse length of 12 ns. The results showed that the improvement of the LIDT after annealing was due to the reduced substoichiometric and structural defects present in the film. The LIDT increased slightly below 573K and then increased significantly with increase in annealing temperature, which could be attributed to different dominant defects. Moreover, the root mean square (RMS) roughness and scattering had little effect on the LIDT, while the absorption and the LIDT were in accord with a general relation. (c) 2008 Elsevier Ltd. All rights reserved.

Passive Q-switching modelocked Yb3+-doped fibre laser with GaAs absorber grown at low temperature

GaAs absorber was grown at low temperature (550degreesC) by metal organic chemical vapour deposition (MOCVD) and was used as an output coupler with which we realized Q-switching modelocked Yb3+-doped fibre laser. The shortest period of the envelope of the Q-switched modelocking is about 3mus. The modelocking threshold is 4.27W and the highest average output pulse power is 290 mW. The modelocking frequency is 12 MHz.

Period Continuous Tuning of an Efficient Mid-Infrared Optical Parametric Oscillator Based on a Fan-out Periodically Poled MgO-Doped Lithium Niobate

We report a period continuously tunable, efficient, mid-infrared optical parametric oscillator (OPO) based on a fan-out periodically poled MgO-doped congruent lithium niobate (PPMgLN). The OPO is pumped by a Nd:YAG laser and a maximum idler output average power of 1.65 W at 3.93 mu m is obtained with a pump average power of 10.5 W, corresponding to the conversion efficiency of about 16% from the pump to the idler. The output spectral properties of the OPO with the fan-out crystal are analyzed. The OPO is continuously tuned over 3.78-4.58 mu m (idler) when fan-out periods are changed from 27.0 to 29.4 mu m. Compared with temperature tuning, fan-out period continuous tuning has faster tuning rate and wider tuning range.

Experimental and theoretical analysis of nondegenerate ultrabroadband chirped pulse optical parametric amplification

Experimental investigations of nondegenerate ultrabroadband chirped pulse optical parametric amplification have been carried out. The general mathematical expressions for evaluating parametric bandwidth, gain and gain bandwidth for arbitrary three-wave mixing parametric amplifiers are presented. In our experiments, a type-I noncollinear phase-matched optical parametric amplifier based on lithium triborate, which was pumped by a 5-ns second harmonic pulses from a Q-switched Nd:YAG operating at 10 Hz, seeded by a 14-fs Ti:sapphire laser at 800 nm, was presented. The 0.85 nJ energy of input chirped signal pulse with 57-FWHM has been amplified to 3.1 muJ at pump intensity 3 GW/cm(2), the corresponding parametric gain reached 3.6 x 10(3), the 53 nm-FWHM gain spectrum bandwidth of output signal has been obtained. The large gain and broad gain bandwidth, which have been confirmed experimentally, provide great potentials to amplify efficiently the broad bandwidth femtosecond light pulses to generate new extremes in power, intensity, and pulse duration using optical parametric chirped pulse amplifiers pumped by powerful nanosecond systems.

Stacking chirped pulse optical parametric amplification

Stacking chirped pulse optical parametric amplification based on a home-built Yb(3+)-doped mode-locked fiber laser and an all-fiber pulse stacker has been demonstrated. Energic 11 mJ shaped pulses with pulse duration of 2.3 ns and a net total gain of higher than 1.1 x 10(7) at fluctuation less than 2% rms are achieved by optical parametric amplification pumped by a Q-switched Nd:YAG frequency-doubled laser, which provides a simple and efficient amplification scheme for temporally shaped pulses by stacking chirped pulse. (C) 2009 Elsevier B.V. All rights reserved.

Reduce of threshold of laser inducing breakdown in atmosphere by introducing an electric spark

We report laser-generated plasmas in atmosphere with electrical spark generated by a synchronization circuit. The breakdown thresholds under the conditions that the electrical spark is used and not used are compared. The breakdown threshold has a distinct decrease after the electrical spark is used. Breakdown thresholds as a function of atmosphere pressure have also been measured at laser wavelengths 532 nm and 1064 rim for the laser pulse width of 15ns. We also discuss the principle and performances of the ionized atmosphere by Nd:YAG laser under the condition of electrical spark introduction. Multiphoton ionization and cascade ionization play important roles in the whole process of atmosphere ionization. The free electron induced by electrical spark can supply the initialization free electron number for multiphoton ionization and cascade ionization. A model for breakdown in atmosphere, which is in good agreement with the experimental results, is described.

ICP-OES的悬浮进样方式及ICP-MS的碰撞/反应池技术的研究与应用

本论文分为两部分：1. 综述部分（第一章和第二章），评述了悬浮进样方式在电感耦合等离子体发射光谱法（ICP-OES）中的研究与应用；电感耦合等离子体质谱（ICP-MS）中碰撞/反应池技术研究的新进展。2. 实验部分（第三章至第九章），内容包括针对不同性质的样品悬浮液选择适当的稳定剂和悬浮雾化ICP-OES的校准方法研究；以混合碰撞/反应气体解决难度较大的高纯氧化钕中稀土杂质测定的干扰问题；以及浊点萃取-石墨炉原子吸收法测定环境样品中痕量镉、氢化物发生-原子荧光光谱法测定铅基合金中砷和植物样品中锗等实用性强的分析方法研究。 ICP的传统进样方式是将样品转化成水溶液形式，以溶液方式进样。然而大多数样品是以固态形式存在，许多样品相当难溶或难熔。采用直接固体进样方法对这些样品进行分析，是分析工作者追求的目标之一。悬浮液进样是一种固体直接进样方法，除了具有其它固体进样技术的优点外，其最大优点是可以像溶液雾化一样用标准水溶液校准。本研究针对实际分析工作中遇到的具体样品，对悬浮进样ICP-OES技术进行了比较深入的研究，成功解决了样品处理繁琐和样品难以处理等困难。对特殊地质样品和激光晶体材料（Nd:YAG）的悬浮进样分析进行了探索。主要工作为：①建立分析地质样品中主量和微量元素的方法，标准水溶液可以成功地用于校准。优点是可以同时对地质样品中的Si和其它元素进行分析，避免了传统分析时需分别处理样品的麻烦。②探索了分析铌钽矿中铌和钽的应用。由于铌和钽具有强抗化学腐蚀性，所以溶液进样分析时样品处理过程复杂。结果表明，以标准水溶液校准时，只要样品研磨时间延长至5 h，即可获得悬浮进样的满意的回收率。③研究了分析掺钕钇铝石榴石(Nd:YAG)中钕掺杂量的可行性。研究表明，加入适量聚丙烯酸作分散剂并调节pH为6，可以得到稳定悬浮液；以通用标准加入法（GSAM）校准可以得到满意的结果。 我国的稀土资源占世界的80％以上，高纯稀土氧化物是高科技领域中的重要材料。碰撞/反应池技术是目前四极杆ICP-MS消除干扰的先进技术，可以选择性地减少某些基体干扰，使背景和检测限得到显著的改进。本实验选择氧化钕（有7个同位素）作为研究对象，采用碰撞/反应池技术重点解决四极杆ICP-MS方法对高纯Nd2O3中稀土杂质进行测定时，基体Nd对Tb、Dy和Ho严重的氧化物或氢氧化物干扰难题。研究结果如下：①在四极杆高分辨率模式下，可以消除Nd对Pr的相邻峰的拖尾干扰；②采用碰撞/反应池技术，设计了10% O2-10% Ar-80% He混合气体作为碰撞/反应气，将Tb、Dy和Ho分别转化为相应的氧化物离子进行测定，成功地消除了基体Nd对Ho的干扰；Nd对Tb和Dy造成干扰的表观浓度显著降低。本方法可直接测定纯度为6N的高纯Nd2O3中的Ho；对纯度为6N的高纯Nd2O3中的Tb和Dy进行扣除，可以分析纯度达5N的高纯Nd2O3中的Tb和Dy。与文献报道的其它消除基体Nd干扰的方法相比较，此方法能够对纯度更高的Nd2O3进行直接分析，且操作简便。此方法也可进一步拓宽，有望解决其它轻稀土氧化物对中重稀土检测的质谱干扰问题。 论文的7～9章的工作包括：浊点萃取-GFAAS测定环境样品中痕量镉、HG-AFS分析铅基合金中砷和植物样品中锗的研究。针对实际分析工作中的具体困难，以上工作分别解决了分析元素含量低、测定干扰严重及样品处理的问题，建立了实用性强、准确度高的分析方法，具有实际应用价值。

1.2 kW高功率1319 nm波长全固态激光器

近年来,高功率1319 nm波长全固态激光器成为激光领域的研究热点之一,它可以广泛应用于光纤通信、激光医疗、频率转换、激光武器等领域.本实验室采用独特的双棒串接热补偿技术,通过对Nd:YAG激光晶体主振荡波长1064 nm及次振荡波长的抑制,实现了最高输出功率为1261 W的1319 nm波长激光输出,光光转换效率为21.7%.

LBO晶体非临界相位匹配倍频研究

利用LBO晶体对Nd:YAG ns激光器进行了腔外倍频实验研究,实验中LBO晶体采用I类非临界相位匹配(NCPM),温度调谐,将倍频转换效率和温度调谐的理论值与实验数据进行了对比,实验结果基本与理论值相符,当基频光的单脉冲能量为1.3J时,获得了840mJ的532nm倍频绿光输出,最高转换效率达到65%,倍频光能量不稳定度小于±3%

I类非临界相位匹配的LBO腔外倍频660nm效率的研究

报道了利用LBO晶体对Nd:YAG纳秒激光器进行腔外倍频实验的研究结果，实验中LBO晶体采用I类非临界相位匹配（NCPM），温度调谐。实验证明，采用LBO温度调谐方式具有倍频效率高、稳定性好、易于调节等优点，当匹配温度为8.4 ℃、基频光功率为1.3J时，获得了855mJ的660nm倍频光输出，最高转换效率达到66%，倍频光能量稳定度小于±3%。

Influence of processing medium on frictional wear properties of ball bearing steel prepared by laser surface melting coupled with bionic principles

Coupling with bionic principles, an attempt to improve the wear resistance of ball bearing steel (GCr15) with biomimetic units on the surface was made using a pulsed Nd: YAG laser. Air and water film was employed as processing medium, respectively. The microstructures of biomimeitc units were examined by scanning electron microscope and X-ray diffraction was used to describe the microstructure and identify the phases as functions of different mediums as well as water film with different thicknesses. The results indicated that the microstructure zones in the biomimetic specimens processed with water film were more refined and had better wear resistance increased by 55.8% in comparison with that processed in air; a significant improvement in microhardness was achieved by laser surface melting. The application of water film provided considerable microstructural changes and much more regular grain shape in biomimetic units, which played a key role in improving the wear resistance of ball bearing steel. (c) 2010 Elsevier B.V. All rights reserved.

应变率对异种不锈钢激光焊接件力学性能的影响

<正>本文采用3kw连续波Nd:YAG激光器对304不锈钢和316不锈钢进行焊接,并在中国科学院力学研究所材料试验机上进行了不同应变率的拉伸试验,同时进行了焊缝处的金相分析。实验表明,应变率对304与316不锈钢焊接件的力学性能有比较明显的影响,试件断口大部分断裂在抗拉强度较低的304不锈钢侧,随着应变

Characteristics of plasma induced by interaction of a free-oscillated laser pulse with a coal target in air and combustible gas

Plasma in the air is successfully induced by a free-oscillated Nd:YAG laser pulse with a peak power of 10(2-3) W. The initial free electrons for the cascade breakdown process are from the ablated particles from the surface of a heated coal target, likewise induced by the focused laser beam. The laser field compensates the energy loss of the plasma when the corresponding temperature and the images are investigated by fitting the experimental spectra of B-2 Sigma(+) -> X-2 Sigma(+) band of CN radicals in the plasma with the simulated spectra and a 4-frame CCD camera. The electron density is estimated using a simplified Kramer formula. As this interaction occurs in a gas mixture of hydrogen and oxygen, the formation and development of the plasma are weakened or restrained due to the chaining branch reaction in which the OH radicals are accumulated and the laser energy is consumed. Moreover, this laser ignition will initiate the combustion or explosion process of combustible gas and the minimum ignition energy is measured at different initial pressures. The differences in the experimental results compared to those induced by a nanosecond Q-switched laser pulse with a peak power of 10(6-8) W are also discussed. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

42CrMo激光焊焊缝组织

42CrMo合金钢C含量高、合金元素含量多、淬硬倾向大,焊接性能差。激光焊接具有功率密度高、焊接变形小等优点,适合焊接传统工艺难焊的同种或异种金属。通过额定功率为3kW的Nd∶YAG固体激光器焊接42CrMo,采用光学显微镜(OM)、扫描电镜(SEM)、X衍射、硬度仪分析了焊缝区域组织、成分和硬度变化。研究结果表明:焊缝区域组织为马氏体,热影响完全淬火区的组织为马氏体+贝氏体组织,热影响不完全淬火区的组织为贝氏体。从焊缝正面到焊缝背面的硬度分布表明:由于焊缝正面有保护气体的作用提高了焊缝正面熔池的冷却速度,使焊缝背面的硬度低于焊缝正面的硬度。