Infrared image upconversion using two-photon resonant optical four-wave mixing in alkali metal vapors

We present a theoretical and experimental study of IR image upconversion using two-photon resonant optical four-wave mixing in alkali metal vapors. A closed form solution for the upconversion efficiency which includes Doppler broadening of the two-photon transition and a finite bandwidth pump laser is given. Experimental results for two types of image upconverters using Cs are presented. The first upconverts 2.94 μm to 4558 Å with a power efficiency of 32 percent and resolvable spots. The second is IR tunable, but of lower efficiency and resolution. Finally, the optimized characteristics of the Cs upconverter are compared to crystal upconverters and to the requirements of various applications.