The effect of the anomalous dispersion on the resonant four wave mixing in ammonia

By means of an interferometric technique we have determined the refractive index of ammonia for the 9P18-9P26 CO2 lines. A calculation model is also reported to derive from these refractive index measurements the dispersion contribution of the sR(3,K) multiplet, resonant with the 9P20 line. This dispersion is the main responsible of the phase mismatching of the resonant four waves MIR generation observed under the strong resonant Raman scattering of this CO2 line in ammonia. The calculated corresponding time modulation is in good agreement with the observed modulation of the experimental MIR pulses.