Development of nonlinear optical crystals for the generation of deep-ultraviolet light

Abstract

Deep-ultraviolet coherent light with a wavelength conversion method that combines infrared solid-state lasers and non-linear optical crystals has been widely used as a light source for inspecting semiconductor photo masks and wafers. Also, in recent years, in order to be used in laser processing applications for material with poor workability, such as glass composite substrates and carbon fiber reinforced plastics, the output power of the light source has become more powerful. Crystals used at the final stage of the wavelength conversion are a particularly critical element to determine the output and life of the light source. The author has been involved for a long time in researching CsLiB₆O₁₀ (CLBO), a borate crystal, which has superior deep-ultraviolet light conversion properties. This article explains this field, while chronologically looking back at the development of its cultivation technology, the implementation of industrial deep-ultraviolet lasers and recent efforts.