湿法化学刻蚀技术处理抛光熔石英元件

Processing fused silica with wet chemical technology

为了提高熔石英元件的抗激光损伤能力,采用基于氢氟酸刻蚀的湿法化学技术去除元件内的激光损伤诱因。利用不同的氢氟酸溶液处理经氧化铈抛光的熔石英元件,并对元件的刻蚀速率、表面洁净度、粗糙度、透过率和激光损伤性能进行评价。研究结果表明,与传统的静态刻蚀相比,在质量分数为6%的氢氟酸刻蚀溶液中引入能量密度约为0.6 W/cm^2的兆声能量对元件的溶解速率和激光损伤性能没有明显的提升作用;化学刻蚀产生的沉积物对元件表面粗糙度和透过率均有不利影响,且沉积物比例与所用的刻蚀液成分和浓度密切相关;经质量分数6%或12%的纯氢氟酸溶液刻蚀(5±1)μm深度后,熔石英元件的激光损伤阈值相比于未刻蚀元件提升了约1.9倍;熔石英元件的激光损伤性能与表面粗糙度和透过率之间不是简单的线性关系,但激光损伤阈值较理想的元件(>20 J/cm^2@3ns)往往具有较光滑的表面,即表面粗糙度<2 nm,由此可以确定有利于熔石英元件激光损伤性能的刻蚀条件,并获得元件表面粗糙度的控制指标。

HF-based etching is used in this paper to remove laser damage precursors to improve the laser-damage resistance of fused silica optics.Several CeO2-polished samples were post-treated by various HF-based etchants and the responses of etching rate,surface cleanliness,roughness,transmission,and laser damage performance of optics to the etching state,etchant composition,and etched depth were investigated.No solid evidence shows that adding acoustic power^0.6W/cm^2 to 6%wt.HF contributes to either the etching rate or the damage performance of samples.The appearance of etching-induced deposits,which deteriorate both the surface roughness and transmission significantly,is highly dependent on the composition and concentration of the etchant.The damage testing results reveal that 6%wt.and 12%wt.HF can efficiently improve LIDT optics^1.9 times the value of an un-etched sample with a(5±1)μm material removal value.Moreover,the damage performance of the optics is found to be somewhat isolated with surface root mean square(RMS)roughness and light transmissionandthat surfaces with a high laser-induced damage threshold(LIDT>20 J/cm^2@3ns)are usually smooth with an RMS roughness<2 nm.Therefore,the wet chemical etching condition that yields surfaces with the desired damage performance can be obtained and the control criterion of surface roughness can be determined.