Enhancement of nonlinear-optical signals under coherent-population-trapping conditions

We develop a nonperturbative approach to study the generation of nonlinear signals in a coherently prepared medium. Specifically, we study the process ω₁-ω₂+(ω₂+Ω), in a system prepared in a coherent-population-trapping state. We calculate enhancement factors of the order of ~10² in the generated signal, under a variety of conditions thus supplementing the work of Jain et al. [Phys. Rev. Lett. 77, 4326 (1996)]. Our approach also enables us to study other related issues. We demonstrate the existence of pulse matching at higher probe powers.