Two-photon resonant four-wave mixing and multiphoton ionization of cesium in a heat-pipe oven

Optical pumping of cesium vapor in a heat-pipe oven in which the energy of two near-infrared photons is close to the 6D states results in high conversion efficiency (up to 1.7%) of the near-infrared pump light to intense blue, forward-propagating radiation. The blue light corresponds to the 7P-6S transition. The dependence of conversion efficiency upon focusing conditions, cell length, and pump intensity is presented. Absorption and gain coefficients are measured in a second heat pipe. The results are discussed in terms of optically pumped stimulated emission (OPSE), stimulated electronic Raman scattering (SERS), and subsequent nonlinear four-wave mixing of two pump-laser photons and one SERS or OPSE infrared photon, leading to parametric generation at ω=2${\omega }_L$-${\omega }_{\mathrm{ir}}$. Two-photon resonant, three-photon ionization cross sections are also studied experimentally and theoretically for the case of resonant enhancement at the 6D levels of cesium. For comparison, similar results for rubidium are also presented for the 5D levels.