Surface machining characteristics of sapphire with fifth harmonic YAG laser pulses

Abstract

In order to reduce the thermal influences in laser machining of sapphire surface such as reattachment of molten material, cracks, etc., effects of a short-pulse ultraviolet laser were investigated. For the ultraviolet laser, the Fifth harmonic generation (Fifth HG) wave of an Nd:YAG laser (wavelength: 213 nm) was utilized. It was shown that significant reduction of thermal damages on the surface was demonstrated with the Fifth HG pulses compared to longer wavelengths of the Nd:YAG laser, such as fundamental (1064 nm), Second HG (512 nm), Third HG (355 nm). Also hole-drilling and surface grooving characteristics were investigated. It was found that the control of depth of the hole and groove with reduced thermal influences was possible in lower fluence cases (less than 40 J/cm 2) with a homogenized beam. Moreover, it was shown that smooth bottom surfaces with their roughness Ra <1 μm could be obtained.