Conversion of the frequency of $He-Ne$-laser radiation from $\lambda=1,15\mu m$ to 377.6 nm in thallium vapor

Infrared helium-neon laser radiation ($\lambda=1,15\mu m$) was transformed to the ultraviolet range ($\lambda=377,6$ nm) in thallium vapor by parametric mixing with radiation from a rhodamine $6G$ dye laser ($\lambda=568,6$ nm). Use was made of a two-photon resonance of the pump (dye laser) radiation with the $6P_{1/2}-7P_{3/2}$ forbidden transition and of the proximity of the frequency of the radiation being temsformed to the frequency of the $7P_{3/2}-7S_{1/2}$ transition.