Effects of phase-conjugate feedback on the modal content and noise characteristics of a cw argon ion laser: experimental results

Significant optical noise reduction can occur in a continuous wave argon io n laser when a very small fraction of the output beam is reinjected inside the laser cavity. Noise reduction reaching 15 dB for the low-frequency comp onents (below 1 MHz) and reaching 58 dB at the frequencies corresponding to the beating of longitudinal modes has been obtained by optimizing the exte rnal cavity length and the feedback level. It has been possible to reduce t he number of oscillating longitudinal modes from similar to 40 to 2 without loss of power. We have compared the optical noise reduction for an externa l cavity terminated by a phase-conjugate mirror and by a conventional plane mirror. (C) 2001 Published by Elsevier Science B.V.