It is common practice to implement process controls and supplement etching techniques to mitigate, limit, and remove redeposition of process compounds during the final stages of polishing of optical substrates used in low absorption and or high-power laser applications.
To ensure optimal performance, Blue Ridge Optics uses process controls and acid etching during all stages of fabrication, from initial blanking and grinding through various stages of the step-down mechanical polishing process to ensure near complete removal of deposited process compounds.
Using Corning 7979/0A substrate material at 25.4mm OD, 6mm CT, Blue Ridge Optics technicians polished 10 substrates (set 1, control) using a standard conventional polishing method which included a standard lapping process, material removal controls to mitigate redeposition, post fabrication acid etch, followed by MRF finishing. A second set of 10 substrates (set 2) from the same raw material batch/lot followed a similar process with the addition of acid etching at post: blanking, centerless grinding, surface grinding, pre-polish, and final polish. Set 2 showed a 25% decrease in bulk raw material absorption pre-coating on three randomly selected samples as compared to set 1. Next, two substrates from each set 1 and 2 were AR coated at 1064nm and laser damage threshold tested @ 10nsp. Set 2 showed a 15% increase in threshold compared to set 1.
While target results were met, further testing is required due to the small sample size.