Float-polishing process and analysis of float-polished quartz.

A fluid-mechanical model is developed for the float-polishing process. In this model laminar flow between the sample and the lap results in pressure gradients at the grooves that support the sample on a fluid layer. The laminar fluid motion also produces supersmooth, damage-free surfaces. Quartz substrates for applications in high-stress environments were float polished, and their surfaces were analyzed by optical scatterometry, photoacoustic spectroscopy, and atomic force microscopy. The removal of 100 µm of material by a lapping-polishing process, with final float polishing, left low levels of subsurface damage, with a surface roughness of approximately 0.2-nm rms.

Subsurface damage identification in optically transparent materials using a nondestructive method.

Total internal reflection microscopy has been applied to image subsurface damage sites in conventionally polished fused-silica flats. This technique can differentiate between surface and subsurface features by changing the illuminating polarization. The method is nondestructive, and no surface preparation is required other than a thorough cleaning of the surface. The intensity distributions in the illuminated region of interest are discussed. The technique has been used successfully as an optical fabrication in-process diagnostic.