Resonant anti-stokes generation of the rotational Raman scattering in NH3 and CH3F

The anti-stokes scattering corresponding to a resonant rotational Raman scattering has been observed in NH3 and CH3F. The anti-stokes frequency is resonant with a transition of the overtone vibrational band n = 0 → 2, and it is generated by mixing the pump with a resonant rotational stokes emission induced inside the vibrational level n = 1. The gain of this anti-stokes scattering is very weak but, due to the mixing nature of the anti-stokes process, a detectable emission is produced when an high gain rotational Raman scattering is induced by means of an high power pump and a suitable stokes resonator.