Noise reduction, lasing without inversion, and pump statistics in coherently prepared λ quantum-beat media

Abstract
Amplitude-noise reduction and diminished losses are found in a laser system in which the lower level of the usual two-level atom is replaced by a coherently prepared doublet, i.e., a λ quantum-beat configuration. The role of atomic coherence between the various levels and regular pumping is investigated. When a portion of the output signal is reflected from a phase-conjugate mirror and reinjected into the laser, the locking phase can be altered and a large phase-noise reduction can be obtained.