Continuous frequency up-conversion in a double-Λ scheme of Na2

 In a double-Λ level configuration of Na₂ molecules, involving rotational–vibrational levels of the X, A and B bands, continuous resonant frequency mixing ω₄=ω₁−ω₂+ω₃ is demonstrated. A DCM dye laser at 661 nm (λ₁) pumps a molecular Raman laser at 746 nm (λ₂) in a sodium heatpipe, which is used to generate the molecular vapour. In the same heatpipe, both fields are mixed with the radiation of an argon-ion laser at 514 nm (λ₃) to generate up-converted laser radiation at 473 nm (λ₄). For laser powers of 200 mW (λ₁), 700 mW (λ₂, internal power) and 140 mW (λ₃), an output power of 120 μW (λ₄) has been achieved. Dependences of the generated radiation on the pump fields (powers and detunings) and polarization features are presented; influences of coherent coupling and population transfer mechanisms are discussed. Received: 7 October 1996