Recent progress in the development of KBe2BO3F2: a deep-UV nonlinear optical crystal

This review mainly introduces in detail the progress of KBBF crystal over the last decade, with a full description of its crystal growth, new phase in hydrothermal growth, revised Sellmeier equations of the refractive index, improved prism-coupled devices, and the related new deep-UV laser sources. Several important applications on angle-resolved photoemission spectroscopy will be reviewed. Finally, we give a prospect about the future development of KBBF crystals.