Subsurface damage measurement of ground fused silica parts by HF etching techniques

Abstract

Detection and measurement of subsurface damage of ground optical surfaces are of major concern in the assessment of high damage thresholds fused silica optics for high power laser applications. We herein detail a new principle of SSD measurement based on the utilization of HF acid etching. We also review and compare different subsurface damage (SSD) characterization techniques applied to ground and fine ground fused silica samples. We demonstrate good concordance between the different measurements.

Loose abrasive slurries for optical glass lapping

“…Recent contributions mainly focus on a proportional relation between SSD depth and Rt, SSD depth ¼ k Rt, where k is a constant factor. We have shown in a previous work that part of the discrepancy of this proportional factor k, such as reported in the literature, was due to the various preparation methods and measuring principles retained for both surface roughness and SSD [12]. We evidenced a factor of k ¼ 9 for a set of diamond ground samples, in good concordance with results from Miller et al [19] and Suratwala et al [11].…”

“…Their measurements were made on both diamond ground silica samples and loose abrasive lapped samples. If we did confirm a proportionality factor close to 9 on diamond ground fused silica samples [12], current results show that this factor cannot be extended to loose abrasive lapped samples. It means that k is changing with the manufacturing process.…”

“…We qualified and compared some of them on ground surfaces in a previous work [12]. Conse- quently, because of its ease of implementation and its availability, we decided to measure SSD by means of acid etching.…”

“…Conse- quently, because of its ease of implementation and its availability, we decided to measure SSD by means of acid etching. This principle has already been detailed elsewhere [12]. It consists in following the evolution of surface roughness Rt during hydrofluoric acid (HF) etching.…”

“…Hence, efforts have been made by us and many others to measure and understand the impact of each manufacturing process step on the creation of subsurface damage (SSD) under the final fused silica surface [7][8][9][10][11]. In a previous contribution, we studied the impact of diamond grinding and proposed various characterization methods to evaluate the depth of SSD under ground and fine ground surfaces [12]. We herein focus on the next manufacturing step of the polishing process, which is the loose abrasive lapping.…”