Continuous-wave vacuum-ultraviolet generation at 192 nm by intracavity second-harmonic and sum-frequency generation

Continuous-wave vacuum-ultraviolet (VUV) radiation near 190-200 nm is highly desirable for high-resolution photoemission spectroscopy, precision spectroscopy, and semiconductor metrology, yet compact all-solid-state sources in this spectral region remain challenging due to the limited nonlinear materials and complex cascaded conversion schemes. Here, we propose a straightforward approach for achieving a VUV laser in the continuous-wave regime with only two-step nonlinear conversion processes. As a proof-of-principle study, we choose a visible Pr:YLF laser platform: the 522-nm (³P₁→³H₅) laser is at first intracavity frequency-doubled to 261 nm and subsequently sum-frequency mixed with the 721 nm (³P₀→³F₄) transition in β-BaB₂O₄ (BBO), delivering milliwatt-level continuous-wave lasers at 192 nm. The proposed approach with two-step nonlinear-frequency up-conversions offers a markedly simplified path for compact, scalable continuous-wave VUV laser sources across the 190-200 nm spectral region.