Saturation of resonant frequency conversion processes in cadmium vapour

The two-photon resonant up-conversion of coherent radiation from 375 to 159 nm in Cd vapor is investigated experimentally and theoretically for the case of the four-frequency process omega (159) = omega(1040) + 2 omega(375). The 1040-nm component is generated internally by the 375-nm pump which is tuned to the two-photon transition (5s2)(1S0) - (5s6s)(1S0); pump intensities up to 100 MW/sq cm and Cd number densities up to 2 x 10 to the 17th/cu cm are employed. The results are presented graphically and found to agree with numerical calculations based on a semiclassical third-order stationary-perturbation model in which the superposition of stimulated emission and parametric generation accounts for the 1040-nm component and population changes explain the observed saturation effects.