Efficient parametric sum-frequency generation by noncoherent two-photon pumping of metal vapors

Four-photon parametric sum-frequency generation in a randomly modulated (noncoherent) pump field was investigated, and an expression obtained for the quantum conversion efficiency. It was found experimentally that on broadening the pump line by a factor of 20–30 (lowering the spectral density by a factor of 10–20) the quantum conversion efficiency for 9.27 μ radiation in sodium vapor reached 35%, exceeding that for the case of quasimonochromatic pumping.