Abstract

The presence of atomic coherence manifests itself in a wealth of phenomena whose study is a topic of current interest in quantum optics and laser physics Among the most interesting of these phenomena is lasing without inversion (LWI), because of its potential for short-wavelength lasing (e g, in the UV or X-rays spectral domains) For conventional lasers based on population inversion, continuous wave (cw) lasing in these spectral domains is unpractical due to the very large incoherent pump power required to reach lasing threshold In LWI a coherent driving field acting on one transition generates the atomic coherence that relaxes the population inversion condition for laser oscillation in an adjacent transition. This greatly reduces the minimum excited state population required for lasing In previous theoretical work, as well as in the three recent experimental demonstrations of LWI in atomic vapors [1], the coherence generating drive field was imposed from the outside In these proof of principle experiments the frequency up-conversion ratio R = ω_α/ω_β (i e, the ratio of generated laser frequency ω_α to drive laser frequency ω_β) was either smaller or very close to one This was dictated by the desire to mitigate or avoid the negative influence of Doppler broadening for LWI.

© 2000 IEEE