Coherent VUV generation by resonantly-enhanced nonlinear frequency mixing in Cd vapor

Broadly tunable coherent VUV radiation has been generated by two-photon resonant sum-frequency mixing in Cd vapor, using frequency-doubled Nd:YAG laser-pumped dye lasers and the three two-photon resonances
5^{1}S_{0} - 5^{1}D_{2}, - 7^{1}S_{0}
, and
-6^{1}D_{2}
. The generated VUV having no spectral structure covers a wavelength range of 119.6-136.8 nm, and the VUV generation efficiency has been measured as a function of wavelength. Besides the tunable VUV, additional intense VUV lines were observed in a spectral range of 145.3-171.1 nm, which were generated by four-wave parametric and second-harmonic processes. The generation mechanisms of these VUV lines are discussed.