Third-order nonlinearities in molecular hydrogen: Two-photon resonance enhanced third-harmonic generation and Raman scattering

In this paper, we investigate the effects of quantum mechanical interferences on third-order susceptibilities in molecules. First principle calculations for molecular hydrogen are presented and shown to agree with results derived from experimental stimulated Raman gain and spontaneous Raman cross-section data. We predict that 10 percent third-harmonic conversion efficiency in H2at 1 atm without phase matching requires a laser intensity of 150 MW/cm²at 4.81 μm. As little as 5.9-MW power is sufficient when the beam is properly focused. We suggest that resonance Raman scattering (RRS) is a possible scheme for experimentally investigating the interference effects, which tend to reduce the strength of third-order nonlinear susceptibilities.