Limitations and optimization of (near) two-photon-resonant frequency up-converters

This paper considers the limitations of (near) two-photon-resonant frequency up-conversion due to quadratic Kerr effect, two-photon absorption, and Raman scattering. These processes, which are intimately tied to the four-wave mixing process, limit the efficiency and/or the pulse length due to breaking of phase-matching, attenuation, and (de)focusing. General expressions are derived for the limits on the efficiency and the pulse length resulting from these processes. The results of the theoretical analysis are applied to three examples of great practical interest; i.e., tripling of the CO2laser in liquid CO, mixing of IR photons using vibrational nonlinearities, and IR image up-conversion in alkali metal vapors. Several new, important properties of these systems are derived.