Two-photon stimulated emission in laser-driven alkali-metal atoms using an orthogonal pump-probe geometry
We observe and analyze a two-photon continuous-wave optical gain mechanism designed for building a two-photon laser. The two-photon stimulated emission is spectrally isolated and resonantly enhanced using the multilevel structure of 39K, in conjunction with an alternative interaction geometry involving orthogonal beams and polarizations. The observed two-photon laser beam amplification increases linearly with low input laser beam intensity, as expected, and saturates at a gain of 2 × 10-4 at high intensity. A theoretical analysis of the observations is outlined.