Resonant nonlinear frequency conversion in metal vapor

Resonant nonlinear odd-order and even-order processes at low-lying levels of alkalies and alkaline earths are studied. Four-wave frequency mixing was employed in an experiment to convert CO2-laser radiation of 7.47 mW, supplied to an IR-transparent input cell window, to the UV-radiation, with sum-frequency power of 197.2 mW, yielding photon efficiency of 65 percent and power efficiency of 2640 percent; photon efficiency of 12 percent was obtained for the Nd:glass laser. A measurement error of about 15 percent is noted. Finally, sum-frequency mixing, involving even-order nonlinearities appearing in a focused pump field, are also considered.