Dynamics of the optically pumped midinfrared NH3laser at high pump power - Part II: Raman gain and ac stark shifts

Coherent effects produced by high-intensity pumping on (6, 0) in NH3are investigated for both the pure gas and for mixtures with an inert buffer gas. Two different Raman transitions are observed. One is the usual directly pumped Raman transition, and the other is pumped indirectly since it first requires a large population transfer to the upper vibrational level. This population transfer also creates inversion gain, shifted away from line center due to ac Stark shifts, on both transitions. Raman gain coefficients of 10 percent ċ cm^-1and inversion gain coefficients > 2 percent ċ cm^-1are observed, and compared to a combined density-matrix and rate-equation model.