Wave-front reversal of multifrequency continuous emission by Bragg scattering from phase regular inhomogeneities

Abstract

The possibility of wave-front reversal of continuous multifrequency emission with a wide line spectrum (in particular, emission of lasers operating on cascade vibrational-rotational transitions of diatomic molecules, e.g., HF or CO) is analyzed; the reversal is based on Bragg scattering from a spatial phase hologram that is recorded in a resonance-absorbing medium by emission with a frequency different from any of the reversed-signal frequencies. The mechanism of formation of a spatial phase hologram and the features of optical Bragg scattering on such structures are analyzed. It is shown that a scattered wave-front is complex conjugate to one of the waves recording the phase grating. An optical system for wave-front reversal is proposed and the Bragg scattering efficiency is estimated for a particular example. The analysis indicates that the proposed system does not exhibit frequency selectivity and is basically suitable for wave-front reversal of emission with a broad line spectrum. The main problem is to choose a medium with resonance absorption at the center of a multifrequency emission spectrum and with complete transparency for the reversed signal.