Study of thermal behaviors in CO2 laser irradiated glass

To understand mechanisms underlying laser-induced damage of BK7 and fused silica, we calculate the temperature field of the substrates with CO2 laser irradiating at a given laser power and beam radius. We find that the two glasses show different thermal behaviors. A model is developed for estimating the time t to heat the surface of the substrates up to a particular temperature T with cw CO2 laser irradiation. We calculate theoretically the duration t that the samples are irradiated, from the beginning to visual catastrophic damage, with the assumption of damage threshold determined by the critical temperature. The duration t that the samples are irradiated, from the beginning to visual catastrophic damage, is investigated experimentally as well. Here we take the melting point or softening point as the critical temperature, given the thermomechanical coupling properties, which is enough to cause damage for BK7. Damage features are characterized by the sound of visual cracks. Finally, we calculate stresses induced by laser heating. The analysis of stress indicates that the damage of BK7 is due to the stresses induced by laser heating. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

Effects of CO2 laser conditioning of the antireflection Y2O3/SiO2 coatings at 351 nm

Y2O3/SiO2 coatings were deposited on fused silica by electron beam evaporation. A continuous wave CO2 laser was used to condition parts of the prepared samples at different scanning speeds in the air. LAMBDA 900 spectrometer was used to investigate the changes of the transmittance and residual reflection spectrum. A Nomarski microscope under dark field was used to examine the changes of the micro defect density. The changes of the surface roughness and the microstructure of the film before and after conditioning were investigated by AFM and X-ray diffraction, respectively. We found that laser-induced damage threshold (LIDT) of the films conditioning at 30 mm/s scanning speed was increased by more than a factor of 3 over the thresholds of the as-deposited films. The conditioning effect was correlated with an irradiation-induced decrease of the defect density and absorption of the films. (c) 2005 Elsevier B.V. All rights reserved.

Influences of CO2 laser irradiation on the structure and photoluminescence of zinc oxide thin films

CO2 laser irradiation experiments on ZnO thin films are reported. The structural, optical, luminescent and vibrational properties of the samples were investigated by X-ray diffraction (XRD), transmittance, photoluminescence (PL) and Raman measurements. XRD results show that the crystalline of the irradiated films was improved. The (002) peaks of irradiated ZnO films shift to. higher 20 angles due to the stress relaxation in the case of laser beam irradiation. From optical transmittance spectra, all films exhibit high transmittance in the visible range, the optical band edge of irradiated films showed a redshift compared with that of as-grown films. Compared with the as-grown films, the photoluminescence emission (in particular the relative intensities of visible emissions) intensities of irradiated samples enhanced. In the Raman scattering spectral both the A I. and E modes exhibited slight Raman blueshift. (c) 2005 Elsevier B.V. All rights reserved.

Laser-induced damage of Ti O2 Si O2 high reflector at 1064 nm

A high laser-induced damage threshold (LIDT) TiO2/SiO2 high reflector (HR) at 1064 nm is deposited by e-beam evaporation. The HR is characterized by optical properties, surface, and cross section structure. LIDT is tested at 1064 nm with a 12 ns laser pulse in the one-on-one mode. Raman technique and scanning electron Microscope are used to analyze the laser-induced modification of HR. The possible damage mechanism is discussed. It is found that the LIDT of HR is influenced by the nanometer precursor in the surface, the intrinsic absorption of film material, the compactness of the cross section and surface structure, and the homogeneity of TiO2 layer. Three typical damage morphologies such as flat-bottom pit, delamination, and plasma scald determine well the nanometer defect initiation mechanism. The laser-induced crystallization consists well with the thermal damage nature of HR. (C) 2008 American Institute of Physics.

光合作用与环境的研究

该成果收集了近10年来我们对光合作用与环境方面研究的主要文章共57篇，概括为6个方面的内容，其中原始论文52篇，技术方法5篇。主要的新进展与特色为：a)阐 明CAM植物代谢与PEPCK的调节特殊性。鉴别菠萝和芦荟为CAM-PEPCK亚型，PEPCK是其光下C4酸的脱羧酶。首次证明PEPCK受底物和碳代谢中间产物的调控，纯化酶的负效应剂G6P、FBP、PEP及正效应剂Mn2+的作用在于改变酶蛋白的构象。b)首先指出PEPC也是活性氧攻击的靶蛋白，其失活原因在于酶蛋白氧化降解和构象改变。不同光合途径植物对光氧化的敏感性有别。光氧化条件下C3与C4植物产生.O2- 速率、耗散激发能和PSII稳定性有一定差异。脂氧合酶（LOX）抑制光合电子传递的位点在PSII氧化侧和Q和PQ上。c)指出较强的抗氧化能力（清除自由基能力）、抗UV-B能力（积累较多的UV-B吸收物质），提高叶片吸收的光能中非光化学耗散的比例，增高光合电子流向光呼吸、O2和NO2-光还原等电子传递支路的传递速率和比例是森林植物适应于自然光环境的强光的重要保护策略。d)从马尾松年轮的δ13C分析追踪了前80年来亚热带自然林区CO2浓度的上升速率（0.7~2.3μl/L/年）。对森林中不同人类活动干扰地点大气CO2、NOX和SO2浓度的现场检测和主要树种的生理、生化变化研究，证明其与人类干扰活动的形式和强度有关，为全球变化及其后效应提供了有力的证据。通过电脑调控水稻生长大棚的CO2浓度发现不同品种间对高CO2浓度适应性的显著差别，明确了适应性较强的4个品种，并从多种指标证明高CO2浓度对水稻的光氧化损伤具有缓解或防护效应。e)盐藻细胞中甘油和蛋白质受介质盐浓度调控，固定化培养提高甘油分泌量。改进和发展了利用对有机自由基DPPH. 的清除比例与数量来评价植物抗氧化性的简易可行的分光光度法。