Abstract

Polishing plates based on teflon rather than traditional pitch retain their shape for long periods of time. That is, once they are flat they stay flat. We have polished 3-inch diameter lithium niobate crystals flat to better than λ/100 with rms roughness less than the noise in our Talystep machine (0.1 nm). The best silicon sphere we have produced (100 mm diameter) is spherical within 75 nm and we still see room for improvement. We are exploring various polishing agents to find the best material for polishing zerodur, magnesium fluoride, calcium fluoride, various grades of silica, some of the best optical glasses, and silicon, while minimizing subsurface damage. We will describe the procedures we use to commission the teflon plates and show interferograms and micro-roughness results for several of our products. We are currently expanding the upper limit on the diameter of our precision workpieces, hopefully to 8-inch. Another feature of our method is that we can also make rather thin devices as well. The lithium niobate crystal, for example is 0.2 mm thick and has an optical thickness uniformity better than 2 nm over 95% of its area as determined by our digital interferometer.

© 1988 Optical Society of America