Energy deposition at insulator surfaces below the ultraviolet photoablation threshold

A surface deformation technique measures the energy deposited in sapphire and other surfaces upon irradiation by focused excimer laser light. For sapphire, the thermal deformation indicates a linear dependence of absorbed energy on excimer fluence with about 3% of the incident light absorbed per surface at 193 nm. Just below etching threshold this absorbed energy should raise the surface temperature to about 430 K, an insufficient temperature for ablation of Al2O3 by thermal vaporization. In contrast the absorbed energy creates ≲3 electron–hole pairs/oxygen atom, consistent with a photochemical (electronic type) etching process.