Assessment of sub-micron subsurface damage in glass

We present a new experimental method for assessing sub-micron level subsurface damage (SSD) on optical glass. The method correlates surface characteristics such as fracture toughness and Young’s modulus via nanoindentation with penetration depth into the tested surfaces, at different overall penetration depths as revealed by magnetorheological finishing (MRF) spotting techniques. Our results on ground surfaces suggest that low surface roughness does not necessarily imply the absence of SSD. We also compared SSD on surfaces processed by deterministic microgrinding and femtosecond (fs) laser polishing. The fs-laser polished surfaces revealed no detectable SSD, thus establishing the feasibility of fs-laser polishing for precision optical manufacturing.