Abstract

Phase conjugation (PC) processes at degenerate four-wave mixing (DFWM) in the active medium of a pulsed e-beam controlled discharge CO₂-laser were studied both experimentally and theoretically. The experiment was carried out with the following parameters: laser gas mixture CO₂:N₂:He=1:2:4, gas pressure 0.3 bar, active medium length 1.2 m, resonator length 12 m (17.7 m for single line laser), interaction angle ~10 mrad at DFWM without optical delay between probe wave and co-propagating pump one. Integral PC reflectivity (PCR) strongly depends on such parameters as: specific input energy (Fig. 1); intensity ratio for probe J₃ and co-propagating pump J₁ wave (Fig.2); coherency of the laser radiation, that varied by rotation of mutual polarization or with optical delay between probe wave and co-propagating pump one; geometry of DFWM; output mirror reflectance R_out (8-80%) (PCR was maximum with R_out of 8% but best quality of PC signal was observed with R_out =80%); gas mixture composition and pressure, being maximum for a mixture with a low fraction of helium and at higher pressure (up to 0.6 bar). A periodical dependence of PCR on optical delay between probe and co-propagating pump wave with periods 10⁻³ and 10⁻⁵ m was observed. The PCR did not depend on spectral content and a degree of linear polarization of the laser radiation.

© 1998 IEEE