Investigation of laser-induced damage on multi-layer dielectric gratings

We investigate mechanisms of laser induced damage thresholds (LIDTs) of multi-layer dielectric gratings (AIDG,). It is found that the laser damage thresholds of MDGs and unstructured dielectric multi-layer coatings (the substrate of MDG) are 3.15J/cm(2) and 9.32 J/cm(2), respectively, at 1064nm (12ns) with the Littrow angle 51.2 degrees and the TEM00 mode. The laser-induced damage mechanism of multi-layer dielectric is presented with the analysis of the following factors: The dominant factor is the pollution on the corrugated surface, which is induced by the complex manufacture process of multi-layer dielectric gratings; another is the electric field distribution along the corrugated surface. The third reason is due to the reduction in stoichiometry of oxide films, resulting from the manufacture process of etching.

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.

Negative dispersion mirrors in Ta2O5/: SiO2 for femtosecond Ti : Sapphire lasers by using gires-tournois interferometers

We design and experimentally demonstrate some negative dispersion mirrors with optimized Gires-Tournois interferometers. The mirror structure is composed of 38 alternating Ta2O5 and SiO2 layers and could be regarded as two sections: high-reflectivity section consisting of a series of quarter-wavelength optical thickness stacks and negative-dispersion section consisting of only 13 layers. The designed mirrors exhibit the expected performance. These mirrors were fabricated by using ion beam sputtering. By adopting such mirrors, dispersion of a mode-locked femtosecond Ti:sapphire laser has been compensated for mostly. With two series of the mirrors, 32 fs and 15 fs pulses have been obtained respectively.

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

Comparison of femtosecond and nanosecond laser-induced damage in HfO2 single-layer film and HfO2-SiO2 high reflector

HfO2 single layers, 800 run high-reflective (HR) coating, and 1064 ran HR coating were prepared by electron-beam evaporation. The laser-induced damage thresholds (LIDTs) and damage morphologies of these samples were investigated with single-pulse femtosecond and nanosecond lasers. It is found that the LIDT of the HfO2 single layer is higher than the HfO2-SiO2 HR coating in the femtosecond regime, while the situation is opposite in the nanosecond regime. Different damage mechanisms are applied to study this phenomenon. Damage morphologies of all samples due to different laser irradiations are displayed. (c) 2007 Optical Society of America.

Effect of SiO2 protective layer on the femtosecond laser-induced damage of HfO2/SiO2 multilayer high-reflective coatings

Two kinds of HfO2/SiO2 800 nm high-reflective (HR) coatings, with and without SiO2 protective layer were deposited by electron beam evaporation. Laser-induced damage thresholds (LIDT) were measured for all samples with femtosecond laser pulses. The surface morphologies and the depth information of all samples were observed by Leica optical microscopy and WYKO surface profiler, respectively. It is found that SiO2 protective layer had no positive effect on improving the LIDT of HR coating. A simple model including the conduction band electron production via multiphoton ionization and impact ionization is used to explain this phenomenon. Theoretical calculations show that the damage occurs first in the SiO2 protective layer for HfO2/SiO2 HR coating with SiO2 protective layer. The relation of LIDT for two kinds of HfO2/SiO2 HR coatings in calculation agrees with the experiment result. (c) 2006 Elsevier B.V. All rights reserved.

Influence of substrate temperature on properties of MgF2 coatings

Thermal boat evaporation was employed to prepare MgF2 single-layer coatings upon both JGS1 and UBK7 substrates at different substrate temperatures. Microstructure, transmittance and residual stress of these coatings were measured by X-ray diffraction, spectrophotometer, and optical interferometer, respectively. Measurement of laser induced damage threshold (LIDT) of the samples was performed at 355 nm, 8 ns pulses. The results showed that high substrate temperature was beneficial to crystallization of the film. Above 244 degrees C, the refractive index increased gradually with the substrate temperature rising. Whereas, it was exceptional at 210 degrees C that the refractive index was higher than those deposited at 244 and 277 degrees C. The tensile residual stresses were exhibited in all MgF2 films, but not well correlated with the substrate temperature. In addition, the stresses were comparatively smaller upon JGS1 substrates. A tendency could be seen that the LIDTs reached the highest values at about 244 degrees C, and the films upon JGS1 had higher LIDTs than those upon UBK7 substrates at the same temperature. Meanwhile, the damage morphologies showed that the laser damage of the coating resulted from an absorbing center at the film-substrate interface. The features of the damages were displayed by an absorbing center dominated model. Furthermore, the reason of the difference in LIDT values was discussed in detail. (C) 2007 Elsevier B.V. All rights reserved.

多层介质膜脉冲宽度压缩光栅与超短脉冲作用时的性能分析

基于啁啾脉冲放大技术的超短脉冲激光系统是提供超快、超强激光的重要途径，具有良好输出波形和高损伤阈值的多层介质膜脉冲宽度压缩光栅是获得高峰值功率脉冲激光的关键。基于傅里叶谱变换方法和严格模式理论，分析了多层介质膜光栅（MDG）在超短脉冲作用下的光学特性。结果表明，当MDG的反射带宽小于具有高斯分布的入射脉冲的频谱宽度时，-1级反射脉冲呈非对称高斯分布，其前沿出现振荡，并且-1级反射脉冲能量开始剧烈下降，讨论了MDG结构参数对其反射带宽的影响。分析了MDG与超短脉冲作用时的近场光分布，对提高其抗激光损伤特性具

单脉冲飞秒脉冲激光对单层和高反光学薄膜的损伤

用电子柬蒸发的方法在BK7玻璃上制备了ZrO2单层膜和ZrO2／SiO2高反膜，利用掺Ti：sapphire飞秒激光系统输出的中心波长为800nm，脉宽为50fs的激光脉冲对这两种样品进行了激光损伤阈值测试．实验结果表明，ZrO2单层膜的阂值比ZrO2／SiO2高反膜的高；这与传统的纳秒脉冲激光的损伤情况相反．利用光离化和碰撞离化激发电子到导带，形成电子等离子体基本模型并对此现象进行了解释．同时，用显微镜对样品的损伤形貌进行了观测，对损伤的特点进行了表征．

355nm增透膜的设计、制备与性能

用热舟蒸发法结合修正挡板技术制备了355 nm LaF3/MgF2增透膜,并对部分样品进行了真空退火。采用Lambda 900光谱仪测试了增透膜的低反光谱和透射光谱,并考察了其光谱稳定性;使用脉冲8 ns的355 nm激光测试了增透膜的激光损伤阈值(LIDT);采用Normarski显微镜对增透膜的表面缺陷密度和破斑形貌进行了观察。实验结果表明,制备得到的增透膜的剩余反射率较低,光谱稳定性好;真空退火对增透膜的激光损伤阈值没有改善;增透膜的破环形貌为散点形式,结合破斑深度测试表明薄膜的破坏源于薄膜和基底界面的缺陷点。JGS1熔石英基底由于有好的表面状况、固有的高激光损伤阈值和以其为基底的增透膜具有更低的表面场强,使得其上的增透膜有更高的抗激光损伤能力。