GAIN WITHOUT INVERSION IN THE FREQUENCY UP-CONVERSION REGIME

We analyze the general conditions and limitations for the realization of frequency up-conversion via lasing without inversion (LWI). Based o n this analysis we propose a class of schemes in which LWI can be achi eved via optical- or microwave-frequency driving on a weakly allowed t ransition. A noninversion amplification process based on this system i s studied with particular emphasis on propagation effects and Doppler broadening. Amplification of both monochromatic and bichromatic fields is considered and a possible implementation in realistic atoms and io ns is discussed.