Ultra-Precision Machining and Surface Evaluation of Optical Flats for High Power Ultra-Violet Lasers

本研究的最终目标是研制出高精度、高透明或高反射率、高激光损伤阈值和高功率紫外激光响应性的平板光学元件，为高功率检验激光器和激光聚变计划的发展提供帮助。本年度的主要研究内容如下：1）建立了恒温恒湿的超精密加工和测量洁净室。2）利用Nomarski干涉显微镜的照相仪器建立了扫描隧道显微镜（STM），为STM测量微表面结构提供了正确的位置。通过测量每mm有1000个槽的光栅对STM进行了校准，成功地用STM测量了Mn-Zn铁氧体表面，尽管被测材料是不导电的。3）用具有零热膨胀玻璃陶瓷主轴的超精密平面磨床将各种光学玻璃研磨成比光学抛光玻璃更光滑的表面。测量了磨削激光玻璃表面的激光损伤阈值。它是明确的损伤阈值取决于表面粗糙度和污染的研磨表面。4）浮法抛光激光玻璃的激光损伤阈值最高，为30 J/cm^2，是光学抛光激光玻璃的两倍。

The final objects of this study is to develop the flat optical components having high accuracy, high transparency or reflectivity, higher laser damage threshold and higher responsibility for high power lasers of ultra-violet in wavelength, in order to help the development of high power examiner lasers and laser fusion program. This year's study was summarized as follows :1) Clean rooms keeping both constant temperature and humidity have been established for the ultra-precision machining and measuring. Anti-vibration foundations also have set up for ultra-precision instruments.2) A scanning tunneling microscope (STM) has been founded by a photographic instruments for a Nomarski interference microscope in order to show the correct place for measuring the micro-surface structure by STM. The STM has been calibrated by measuring the grating having 1000 grooves per mm. It has succeeded to measure Mn-Zn ferrite surfaces by STM without metal coating, though the measured material is not conductive.3) Various optical glasses have been ground into very smooth surfaces better than optically-polished ones by a ultra-precision surface grinder having a glass-ceramic spindle of zero-thermal expansion. Laser damage thresholds of ground laser glass surfaces have been measured. It is cleared that the damage threshold depends upon the surface roughness and contamination of ground surfaces. Ground surfaces show the higher damage thresholds rather than optically-polished surfaces.4) The float-polished laser glass shows the highest laser damage threshold of 30J/cm^2, which is double number rather than that of optically-polished surfaces.