Generation of VUV/XUV coherent radiation in molecular gases

Tunable coherent radiation of wavelength between 92 nm and 122 nm has been produced in molecular gases of N-2, CO, H-2 and CH4 by resonant and nonreso nant third harmonic generation. Factors with respect to the frequency conve rsion efficiency, including the line strength of the nonlinear susceptibili ty, the density of the media and the phase-matching, are discussed. By anal yzing the characteristics of the four-wave mixing spectra in molecular gase s, some physical parameters and the population of the energy levels are obt ained. This indicates that nonlinear optical frequency conversion process p rovides a useful method to study the structure and spectra of molecules.