Deep-UV laser source based on χ⁽²⁾ optical frequency conversion and χ⁽³⁾ stimulated Raman scattering

By integrating χ⁽²⁾ optical frequency conversion and χ⁽³⁾ stimulated Raman scattering (SRS) technology, we demonstrated a new, to the best of our knowledge, deep-UV laser generation scheme near 200 nm in a non-cryogenic KD₂PO₄ (DKDP) crystal. Based on an Nd:YAG laser (1064 nm, ω₁) and cascaded LiB₃O₅ and DKDP crystals, a 266 nm radiation was obtained firstly by the second- and fourth-harmonic generation (SHG and FHG) (ω₄). The energy conversion efficiency from ω₁ to ω₄ was 24.8%. Meanwhile, the Stokes lights (ω) were stimulated by the Nd:YAG laser in a KGd(WO₄)₂ crystal with two polarization-dependent Raman shifts of 768 cm^-1 and 901 cm^-1. Finally, 3.5 mJ, 216.3 nm, and 3.1 mJ, 217 nm deep-UV laser sources were obtained in a DKDP crystal by the sum-frequency generation (SFG) of ω and ω₄. The total conversion efficiency from 1064 nm infrared to ∼200 nm deep UV was ∼3%. This scheme, by systematically combining the χ⁽²⁾ and χ⁽³⁾ nonlinear effects, overcame the phase-matching limitation of traditional schemes to acquire high-energy 200 nm wave band deep UV via the fifth-harmonic generation (FiHG) in the DKDP crystal, which may provide a new way for the deep-UV laser generation with high energy and high-peak power.