Nonequilibrium mixing of optical frequencies

A study was made of nonequtlibrium mixing of ultrashort laser pulses. The theory was developed for the Gaussian and Lorentzian distributions of the original waves; the latter case was analyzed in detail. Nonequilibrium generation (by a cascade method) of the third harmonic of a laser emitting locked longitudinal modes was observed experimentally. It was predicted theoretically and confirmed experimentally that the width of the spectrum of the harmonic frequency reached saturation under nonequilibrium mixing conditions. The measured spectra of the second and third harmonics generated under quasistatic conditions and the ratio of their widths indicated that the spectrum of a train of ultrashort laser pulses was Lorentzian. Calculations were also made of the characteristic parameters of the nonequilibrium generation of sum frequencies in KDP and CaCO₃ crystals.