Four-photon parametric up-conversion in sodium vapor pumped with monochromatic and noise radiation under strong and weak dispersion conditions

A theoretical investigation is made of the influence of various effects on four-photon parametric upconversion in metal vapors: saturation, one-photon absorption of output radiation, two-photon depletion of pump radiation, wave detuning, and dispersion of the group velocities of the interacting waves. Estimates indicate that the simultaneous influence of all these effects can ensure a fairly efficient up-conversion of noise pump radiation, compared with the monochromatic case. The results agree well with the experimental results obtained in a study of conversion of tunable CO₂ laser radiation in sodium vapor.