O. Pfister et al., Two-photon stimulated emission in laser-driven alkali-metal atoms using anorthogonal pump-probe geometry, PHYS REV A, 60(6), 1999, pp. R4249-R4252
We observe and analyze a two-photon continuous-wave optical gain mechanism
designed for building a two-photon laser. The two-photon stimulated emissio
n is spectrally isolated and resonantly enhanced using the multilevel struc
ture of K-39, in conjunction with an alternative interaction geometry invol
ving orthogonal beams and polarizations. The observed two-photon laser beam
amplification increases linearly with low input laser beam intensity, as e
xpected, and saturates at a gain of 2 x 10(-4) at high intensity. A theoret
ical analysis of the observations is outlined. [S1050-2947(99)50812-3].