199 nm vacuum-ultraviolet second harmonic generation from SrB₄O₇ vertical microcavity pumped with picosecond laser

We have proposed highly efficient microcavity wavelength conversion devices that do not utilize the birefringence or ferroelectricity of crystals. In this study, we utilized a low-birefringence paraelectric SrB 4 O 7 crystal with significant potential for wavelength conversion and high transparency down to 130 nm and succeeded in achieving 199 nm vacuum-ultraviolet second harmonic generation (SHG) with a picosecond laser. The wavelength of 199 nm is shorter than the theoretical minimum for SHG in BaB 2 O 4 of 205 nm. Our device could be a practical vacuum-ultraviolet SHG device, enabling significantly smaller and more efficient vacuum-ultraviolet laser sources compared to conventional systems.