Hui Ye, Yaguo Li, Qinghua Zhang, Wei Wang, Zhigang Yuan, Jian Wang, and Qiao Xu, "Post-processing of fused silica and its effects on damage resistance to nanosecond pulsed UV lasers," Appl. Opt. 55, 3017-3025 (2016)
HF-based (hydrofluoric acid) chemical etching has been a widely accepted technique to improve the laser damage performance of fused silica optics and ensure high-power UV laser systems at designed fluence. Etching processes such as acid concentration, composition, material removal amount, and etching state (etching with additional acoustic power or not) may have a great impact on the laser-induced damage threshold (LIDT) of treated sample surfaces. In order to find out the effects of these factors, we utilized the Taguchi method to determine the etching conditions that are helpful in raising the LIDT. Our results show that the most influential factors are concentration of etchants and the material etched away from the viewpoint of damage performance of fused silica optics. In addition, the additional acoustic power () may not benefit the etching rate and damage performance of fused silica. Moreover, the post-cleaning procedure of etched samples is also important in damage performances of fused silica optics. Different post-cleaning procedures were, thus, experiments on samples treated under the same etching conditions. It is found that the “spraying + rinsing + spraying” cleaning process is favorable to the removal of etching-induced deposits. Residuals on the etched surface are harmful to surface roughness and optical transmission as well as laser damage performance.
Mathilde Pfiffer, Philippe Cormont, Evelyne Fargin, Bruno Bousquet, Marc Dussauze, Sébastien Lambert, and Jérôme Néauport Opt. Express 25(5) 4607-4620 (2017)
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Samples were etched by various etchants to diverse depths, and the S/N ratio of R-on-1 LIDT was used for analysis.
For BOE, the concentration of HF was changed, but was kept constant in concentration () for all the experiments in this table.
Table 3.
Analysis of Variance (ANOVA) of Etching-Related Factorsa
The ultrasonic rinsing process was similar in each treatment.
Spraying 1–3 represents the DI water spraying with different facilities. Spraying 1: automatically sprayed by tank jet (flow is ; nozzle diameter ); spraying 2: manual hosepipe spraying (flow is ; nozzle diameter ); spraying 3: manual squirt gun spraying (flow is ; nozzle diameter ).
Surface roughness and transmission data are taken from the deposited area for most samples, except for clean samples J2, K1, and K2, which are randomly tested on the surface. Measured surface roughness of the reference sample U1 is probably less than the actual value because the surface roughness is beyond the detection limit of the measuring device.
Tables (4)
Table 1.
Etching Process Factors in Our Experiments, Including HF Concentration, Solution Composition, Etched Depth, and Acoustic Power Density
Factors
A
B
C
D
HF Concentration (wt. %)
Composition
Etched Depth (μm)
Acoustic Power Density ()
2
HF
0–1
0
6
BOE ()
0.6
12
/
/
/
/
/
Table 2.
Taguchi Experiment Array and the Results Obtaineda
Samples were etched by various etchants to diverse depths, and the S/N ratio of R-on-1 LIDT was used for analysis.
For BOE, the concentration of HF was changed, but was kept constant in concentration () for all the experiments in this table.
Table 3.
Analysis of Variance (ANOVA) of Etching-Related Factorsa
The ultrasonic rinsing process was similar in each treatment.
Spraying 1–3 represents the DI water spraying with different facilities. Spraying 1: automatically sprayed by tank jet (flow is ; nozzle diameter ); spraying 2: manual hosepipe spraying (flow is ; nozzle diameter ); spraying 3: manual squirt gun spraying (flow is ; nozzle diameter ).
Surface roughness and transmission data are taken from the deposited area for most samples, except for clean samples J2, K1, and K2, which are randomly tested on the surface. Measured surface roughness of the reference sample U1 is probably less than the actual value because the surface roughness is beyond the detection limit of the measuring device.