OBSERVATION OF LARGE CONTINUOUS-WAVE 2-PHOTON OPTICAL AMPLIFICATION

We observe 30% two-photon optical amplification of a probe laser-held propagating through a laser-pumped potassium vapor. This amplification is spectrally isolated and substantially larger than that of previous ly reported continuous-wave two-photon amplifiers. The combination of large amplification and spectral isolation of the two-photon gain feat ure will greatly facilitate precise studies of the photon statistics o f this highly nonlinear quantum amplifier and the development and char acterization of a two-photon laser based on this gain medium. We also observe spectrally-distinct three-photon amplification (similar to 5%) in the same system under different experimental conditions. We presen t a simple model of the interaction that gives qualitative agreement w ith our observations and explains the dependence of the two-photon gai n on the various system parameters. This model predicts that the size of the two-photon gain is quite sensitive to an interference between t wo different quantum pathways.