Influence of absorption on resonant four-photon frequency addition

Experimental and theoretical investigations were made of resonant four-wave frequency addition of the type ω_s = 2ω₁ + ω₂. The gas-concentration dependences of the mixing efficiency varied qualitatively with the ratio of the absorption coefficients of the input and output radiations. Theoretical interpretation of the observed dependences are provided and recommendations are given on selection of the optimal frequency-conversion conditions.