Thermodynamic damage mechanism of transparent films caused by a low-power laser

A new model for analyzing the laser-induced damage process is provided. In many damage pits, the melted residue can been found. This is evidence of the phase change of materials. Therefore the phase change of materials is incorporated into the mechanical damage mechanism of films. Three sequential stages are discussed: no phase change, liquid phase change, and gas phase change. To study the damage mechanism and process, two kinds of stress have been considered: thermal stress and deformation stress. The former is caused by the temperature gradient and the latter is caused by high-pressure drive deformation. The theory described can determine the size of the damage pit. (c) 2006 Optical Society of America.

Ta2O5／SiO2硬膜双腔滤光片激光损伤特性研究

研究了Ta2O5／SiO2硬膜双腔干涉滤光片带内、带边及带外的吸收和激光损伤特性。实验发现，对于作用激光，带通滤光片的驻波场分布、吸收率和损伤阈值在带内、带边和带外的响应特性对作用激光波长均呈现出明显的选择性。根据实验结果，结合滤光片的驻波场分析，给出了带通滤光片的损伤机理。

1064nm与532nm激光对电子束蒸发制备的HfO2／SiO2高反膜损伤比较

研究了电子束蒸发制备的HfO2／SiO2高反膜在1064nm与532nm激光辐照下的损伤行为。基频激光辐照时损伤形貌主要为节瘤缺陷喷溅留下的锥形坑。当能量密度较大时出现分层剥落；二倍频激光损伤主要是由电子缺陷引起的平底坑，辐照脉冲能量密度稍高时也会产生吸收性缺陷引起的锥形坑，但电子缺陷的损伤阈值更低；随着辐照脉冲能量密度的增大分层剥落逐渐成为主要的损伤形貌。分析认为，辐照激光波长的变化。引起吸收机制的变化从而导致了损伤阈值及损伤机制的差异。

Irradiation damage on BaLiF3 crystallites and its suppression by rare-earth ion doping

The x-ray and gamma-ray induced damage in BaLiF3 crystallites and its suppression by rare earth ion doping have been studied by electron spin resonance and thermally stimulated luminescence methods. It has been found that the x-ray irradiation damage is light and can be erased easily. This shows that the BaLiF3 crystallite is an ideal host for x-ray storage material. But the damage induced by gamma-ray has been found to be relatively hard to recover; however the gamma-ray irradiation hardness can be improved by rare earth (e.g., La3+, Yb3+) ion doping. So the BaLiF3 is also promising material for being used in detection of high-energy particles (e.g., gamma-ray).

飞秒激光微加工：激光精密加工领域的新前沿

飞秒激光微加工技术具有加工精度高、热效应小、损伤阈值低以及能够实现真正的三维微结构加工等优点,这些特性是传统的激光加工技术所无法取代的。首先回顾了激光微加工和超短脉冲激光技术的发展历史,然后介绍超短脉冲激光与金属和介质材料相互作用的机制,接着阐述了飞秒激光直写、干涉和投影制备等各种加工方法的原理,重点讨论飞秒激光在三维光子器件集成、微流体芯片制备及其在生化传感方面的应用等,最后展望了飞秒激光微加工领域所面临的机遇和挑战,指出了未来的研究方向。

超短脉冲激光对透明材料的破坏

基于固体的能带理论和能量守恒原理建立了一个描述激光与非金属材料作用时载流子随时间空间变化的理论模型。讨论了材料的破坏阈值、烧蚀深度与激光脉宽、波长和强度之间的关系，同时也讨论了破坏阈值、烧蚀深度与材料禁带宽度等特性之间的关系。讨论了多光子电离、隧道电离和雪崩电离在激光对材料破坏过程中的不同地位，理论结果表明，光电离在超短脉冲激光对非金属材料破坏过程中对破坏阈值的影响最大。

Wideband two-port beam splitter of a binary fused-silica phase grating

The usual beam splitter of multilayer-coated film with a wideband spectrum is not easy to achieve. We describe the realization of a wideband transmission two-port beam splitter based on a binary fused-silica phase grating. To achieve high efficiency and equality in the diffracted 0th and -1st orders, the grating profile parameters are optimized using rigorous coupled-wave analysis at a wavelength of 1550 nm. Holographic recording and the inductively coupled plasma dry etching technique are used to fabricate the fused-silica beam splitter grating. The measured efficiency of (45% x 2) = 90% diffracted into the both orders can be obtained with the fabricated grating under Littrow mounting. The physical mechanism of such a wideband two-port beam splitter grating can be well explained by the modal method based on two-beam interference of the modes excited by the incident wave. With the high damage threshold, low coefficient of thermal expansion, and wideband high efficiency, the presented beam splitter etched in fused silica should be a useful optical element for a variety of practical applications. (C) 2008 Optical Society of America.

溶胶-凝胶多孔二氧化硅减反膜稳定性研究

多孔SiO2膜层经热处理后，具有很高的激光破坏阈值，但是结构中有许多Si-OH亲水基团，导致光学透过率受环境相对湿度的影响很大。实验目的是改善膜层内部结构，使膜层结构中的亲水基团转变为疏水基团。提高膜层的疏水性，增强膜层的透过率稳定性。系统地研究了膜层透过率随时间变化的规律，在氨气和六甲基二硅氮烷(HMDS)混合气氛下热处理膜层，处理后生成Si-O-Si(CH2)3非极性疏水基团，使膜层的疏水性大大提高，因而膜层的透过率稳定性有大幅度提高。稳定性的提高延长了膜层的寿命。处理后膜层的表面粗糙度良好，均方根表

透红外含碲氟铝基玻璃的激光损伤阈值

在氟铝酸盐玻璃组分中加入适量声子能量低的重金属氧化物TeO2，得到一种新的氧氟化物玻璃。该材料具有良好的成玻璃性能，适合制作大尺寸红外窗口镜。研究了TeO2含量对玻璃特征温度、阿贝数和红外透过性能的影响。同时测试了这种玻璃的抗DF激光能力，结果表明：TeO2含量为15％的玻璃，DF激光破坏阈值达14．95kW·cm^-2。分析显示，由于玻璃基质的多声子吸收，对激光能量的吸收而引起的热冲击是导致玻璃破坏的主要原因。进一步降低玻璃中水分，可以提高玻璃抗激光破坏性能。

HfO2 膜料中的杂质对薄膜损伤及性能的影响

By analysis of impurity elements in HfO2 coating material, the influence of main impurity elements on the characteristic of coatings were studied. The results indicate that the metal elements and absorptive dielectric elements damage the HfO2 coatings. The more the Zr element content is, the more the absorption is for the coatings in ultraviolet wave. The negative ion element will become the gas source center and form an ejection in the process of evaporation of coating material, so decrease the damage threshold of the coatings.

电子束蒸发制备平板偏振膜激光损伤特性研究

采用电子束蒸发沉积技术制备了平板偏振膜。用Lambda900分光光度计测试了其光学性能。在中心波长1053nm处P偏振光的透过率Tp〉98％，S偏振光的透过率Ts〈0．5％，消光比T，／瓦〉200：1，带宽约为20nm。用波长1064nm，脉宽12ns的脉冲激光进行损伤阈值测试，获得P偏振光的损伤阈值为17．2J／cm^2，S偏振光的损伤阈值为19．6J／cm^2。用Nomarski显微镜对薄膜的损伤形貌进行观察，并用Alpha-500型台阶仪对损伤深度进行测试。结果表明，P偏振光的激光损伤为界面损伤与缺

多层介质膜光栅和介质膜反射镜抗激光损伤阈值研究

对多层介质膜光栅以及介质膜反射镜的激光损伤阈值进行了系统的研究。测试方法采用国际测试标准。测试结果表明，介质光栅的损伤阈值远低于未刻蚀的多层介质膜。对样品损伤形貌的扫描电镜照片分析发现，相比于未刻蚀的多层介质膜，介质膜光栅的初始损伤主要发生在光栅槽形的侧壁，且损伤主要是由驻波场的空间分布引起的本征吸收、制备过程中引入的杂质污染以及刻蚀过程中HfO2的化学计量机失衡引起的。

重复率激光作用下光学薄膜损伤的累积效应

使用脉宽12ns，频率10Hz的1064nm调Q Nd：YAG激光器，研究了高反射膜在重复率激光作用下的损伤的累积效应。实验发现，高反射膜的损伤阈值随辐照脉冲数增加而降低，表现出明显的累积效应。通过对损伤阈值和损伤概率以及辐照次数的统计性研究．并结合单脉冲辐照的结果，说明了存在于薄膜中微小的缺陷参与了多脉冲激光对薄膜的损伤过程。可用预损伤机制解释实验结果。得到了关于IBS制备的高反射膜的损伤阈值和照射次数的关系式，并用实验结果进行验证．发现具有很好的一致性。实验过程中样品的损伤形貌通过Nomarski偏光

不同沉积参量下ZrO_2薄膜的微结构和激光损伤阈值

ZrO2采用X射线衍射(XRD)技术分析了不同充氧条件和沉积温度对ZrO2溥膜组成结构的影响，并对不同工艺下制备的薄膜的表面粗糙度和激光损伤阈值进行了测量。结果发现随着氧压的升高，ZrO2溥膜将由单斜相多晶态逐渐转变为非晶态结构，而随着基片温度的增加，溥膜将由非晶态逐渐转变为单斜相多晶态。同时发现随着氧压升高晶粒尺寸减小，而随着沉积温度增加，晶粒尺寸增大。氧压增加时工艺对表面粗糙度有一定程度的改善，而沉积温度升高，工艺对表面粗糙度的改善不明显。晶粒尺寸大小变化与表面粗糙度变化存在对应关系。激光损伤测量表明

多脉冲激光作用下光学薄膜损伤的累积效应

研究了高反射膜在多脉冲激光作用下损伤的累积效应．实验中使用1064nm调Q的Nd：YAG激光器，脉宽是12ns，频率为10Hz．实验发现：高反射膜的损伤阈值随辐照脉冲数增加而降低，表现出明显的累积效应．通过对损伤阈值和损伤概率以及辐照次数的统计性研究，并结合单脉冲辐照的结果，说明了存在于薄膜中微小的缺陷参与了多脉冲激光对薄膜的损伤过程，得到了制备IBS高反射膜的损伤闽值和照射次数的关系式，用Nomarski偏光显微镜观察了实验过程中样品的损伤形貌，发现是典型的缺陷损伤．