Fabrication of optical glass lenses using laser slicing technology (Stress formation and crack propagation mechanism in internal laser processing)

Abstract

Laser slicing technology is a new processing technology to fabricate optical glass lenses by focusing ultrashort laser pulse laser into the glass to form a modified layer. Crack propagation can be generated by forming a modified layer with residual stresses, and three-dimensional machining can be achieved by controlling the crack propagation. The purpose of this study was to elucidate the crack propagation mechanism by the laser slicing of glass. The stress around the modified layer were evaluated using microscopic birefringence evaluation device under various laser irradiation conditions. As a result, it was clarified that crack propagation occurs according to the tensile stress in the modified layer due to volume expansion. The tensile stresses were stronger when the modification layer was densely formed. Using this knowledge, we attempted to fabricate a spherical lens with a diameter of 30 mm and a radius of 100 mm. The stress concentration at the crack edge due to warpage promoted self-crack propagation and successfully produced a spherical lens with a mirror surface.

Keywords

• laser slicing
• glass
• ultrashort pulse laser
• internal modification
• crack propagation