Spectral properties of resonant four-photon parametric oscillation

An investigation was made of the spectral properties of four-photon parametric oscillation when the frequency of the generated field is tunable near an atomic resonance line. An ω₄ = ω₁–ω₂+ω₃ generation process involving coherent anti-Stokes scattering in thallium vapor was achieved experimentally. Biharmonic pumping was provided by resonant excitation of a 6P_1/2–6P_3/2 two-photon transition at the frequency ω₁–ω₂. Measurements were made of the oscillation power when the frequency ω₃ was tunable near the frequency of a 6P_3/2–7D_3/2 transition at various thallium vapor pressures. It was found that the spectral properties of resonant parametric oscillation depend strongly on the concentration of active-mixture atoms and also on various saturation effects.