Lasing in barium vapor in a resonant optical field

Lasing was achieved in barium vapor near an absorption line at the λ = 553.5 nm wavelength corresponding to the 6¹S₀–6¹P₁ resonance transition. Barium vapor produced in an arc discharge was placed in the resonator of a dye laser having a stimulated emission spectrum of ~ 5 pm half-width. In the presence of additional "weak" broad-band radiation, the lasing spectrum consisted of two components symmetric relative to the center of the absorption line. This lasing was due to stimulated Raman scattering by a population grating and was most efficient in regions where the difference between the frequencies of the strong and weak fields coincided with the Rabi frequency. A quantitative comparison was made between theory and experiment on amplification without population inversion in a two-level system. Holographic interference spectroscopy was used to study experimentally the behavior of the susceptibility (the absorption coefficient and the refractive index) under conditions of resonant interaction. Good agreement was obtained between the behavior of the dispersion of the refractive index and the theoretical dependence. The highest gains were k_v ≈ 10 cm ^–1 when the barium atomic concentration was N ≈ 5 X 10¹⁶ cm ^–3.