Research progress of deep-UV nonlinear optical crystals and all-solid-state deep-UV coherent light sources

All-solid-state deep ultraviolet coherent light sources have important applications in frontier science, high technology and many other fields. An effective and feasible technical approach is to use commercially available visible and near-infrared all-solid-state lasers as the fundamental frequency light source to generate a deep ultraviolet laser through cascaded frequency conversion using nonlinear optical crystals. This paper reviews the research progress of deep ultraviolet nonlinear optical crystals and all-solid-state deep ultraviolet coherent light sources. Taking KBBF crystals as the representative example, their discovery, crystal growth, corresponding prism-coupled device technology, main optical properties, and ability to generate deep ultraviolet coherent light are each introduced. It was proven that KBBF crystals are excellent nonlinear optical crystals that can achieve deep ultraviolet laser output through direct frequency doubling. The applications of deep ultraviolet coherent light sources based on KBBF crystals and prism-coupled technology are discussed, with special focus given to ultra-high resolution photoelectron spectrometers. Finally, the future direction of the development of deep ultraviolet nonlinear optical crystals and all-solid-state deep ultraviolet laser technology are given.