Generation of single-frequency tunable vacuum ultraviolet laser radiation in solid hydrogen

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The purpose of the present project is to realize useful coherent radiations in vacuum ultraviolet (vuv) region using solid hydrogen as a nonlinear optical material. We have tried to efficiently modulate single-frequency tunable laser radiations around 200 nm with extremely high Raman-coherence in solid hydrogen and generate single-frequency tunable laser radiations in vuv region. In the following, we summarize our principal results.1, We have generated 201nm laser radiation by taking sum-frequency of 266nm- (forth harmonics of YAG laser) and 827nm- (Ti : sapphire laser) laser radiations with energy conversion efficiency of 〜10%. The pulse duration of the generated 201 nm laser radiation was 10 ns with the Fourier transform limited linewidth of 〜 30 MHz.2, We have modulated the single-frequency tunable laser radiations at 201 nm by the Raman-coherence with the frequency of 125 THz that was adiabatically driven in solid hydrogen, leading vuv coherent radiation at 186 nm with quantum efficiency of 〜 8%.3, We have demonstrated laser spectroscopy in vuv region for a transition in Schumann-Runge band (B ^3Σ_<-u> (v'=8, N'=20) ←X ^3Σ_<-g> (v"=0, N"=19), wavelength : 185.987nm) by using the coherent vuv radiation realized above. We have shown that the laser spectroscopy with spectral resolution of 〜 50 MHz is possible in vuv, leading the precise spectral profile and cross section of this transition.