Improving predictability in optical fabrication can go a long way towards increasing profit margins and maintaining a competitive edge in an economic environment where pressure is mounting for optical manufacturers to cut costs. A major source of hidden cost is rework – the share of production that does not meet specification in the first pass through the polishing equipment. Rework substantially adds to the part’s processing and labor costs as well as bottlenecks in production lines and frustration for managers, operators and customers. The polishing process consists of several interacting variables including: glass type, polishing pads, machine type, RPM, downforce, slurry type, baume level and even the operators themselves. Adjusting the process to get every variable under control while operating in a robust space can not only provide a deterministic polishing process which improves profitability but also produces a higher quality optic.
Sandia's Large Optics Coating Operation has extensive results of laser induced damage threshold (LIDT) testing of its
anti-reflection (AR) and high reflection coatings on substrates pitch polished using ceria and washed in a process that
includes an alumina wash step. The purpose of the alumina wash step is to remove residual polishing compound to
minimize its role in laser damage. These LIDT tests are for multi longitudinal mode, ns class pulses at 1064 nm and
532 nm (NIF-MEL protocol) and mode locked, sub-ps class pulses at 1054 nm (Sandia measurements), and show
reasonably high and adequate laser damage resistance for coatings in the beam trains of Sandia's Z-Backlighter terawatt
and petawatt lasers. An AR coating in addition to coatings of our previous reports confirms this with LIDTs of 33.0
J/cm<sup>2</sup> for 3.5 ns pulses and 1.8 J/cm<sup>2</sup> for 350 fs pulses. In this paper, we investigate both ceria and zirconia in doublesided
polishing (common for large flat Z-Backlighter laser optics) as they affect LIDTs of an AR coating on fused silica
substrates washed with or without the alumina wash step. For these AR coated, double-sided polished surfaces, ceria
polishing in general affords better resistance to laser damage than zirconia polishing and laser damage is less likely with
the alumina wash step than without it. This is supported by specific results of laser damage tests with 3.5 ns, multi
longitudinal mode, single shot pulses at 1064 nm and 532 nm, with 7.0 ns, single and multi longitudinal mode, single
and multi shot pulses at 532 nm, and with 350 fs, mode-locked, single shot pulses at 1054 nm.