Tunable UV coherent radiation and infrared stimulated radiation generated by hybrid pumping in the Na2-Na system

Abstract

For the first time by means of two-photon hybrid excitation in the Na2-Na system, which is distinguished from the usual two-photon excitation in atomic vapor, tunable UV coherent radiation (between 337.6 and 339.1 nm and between 358.0 and 359.6 nm) and tunable infrared stimulated radiation (3.38-3.46 µm) were generated. By optically pumping with a pulsed dye laser scanning from 614.5 to 617.4 nm for sodium vapor in a heat-pipe oven, Na2 was excited by the first photon absorption from the X ′ Σ g + to the A ′ Σ u + state. The energy was transferred to Na by Na2*-Na collision to populate the levels 3p1/2,3/2 in Na, which was followed by another photon excitation from the same beam up to near the 5S level, resulting in SERS (3P1/2-4P and 3P3/2-4P) and OPSE(5S → 4P and 4P → 4S) radiation. Assuming the detunings of pumping frequency ω1, from ω(5S,3P3/2) and ω(5s,3p1/2) to be Δ1 and Δ2, respectively, the three UV coherent radiation components were supposed to be generated by the following mixing processes: ωUV = 2ω1 − ω(5S − 4P); ω U V ′ = 2 ω 1 − [ ω ( 5 S → 4 P ) + Δ 1 ] ; ω U V ′ ′ = 2 ω 1 − [ ω ( 5 S → 4 P ) + Δ 2 ] , and also ω U V ′ ′ ′ = 2 ω 1 − ω ( 4 P → 4 S ) . The SERS and the UV signals were tuned as the pumping wavelength was tuned. The measured wavelengths agreed well with the calculated values.