Spatial-mode cleanup of a pulsed laser beam through mutually pumped phase conjugation with a cw reference

A method of cleaning up the spatial mode of a pulsed laser beam without using a pinhole is proposed and demonstrated. The method consists of performing mutually pumped phase conjugation (MPPC) between the pulsed laser beam and a cw reference, thereby transferring the desirable spatial mode of the cw beam onto the pulsed beam. In these experiments MPPC is observed in a photorefractive BaTiO(3) crystal between the beams from a Q-switched flash-lamp-pumped Nd:YAG laser and a diode-pumped cw Nd:YAG laser, both operating at 532 nm. The experimental results showed convincing spatial-mode cleanup of the pulsed beam, with an approximately 3% conversion efficiency. A method of significantly increasing the overall efficiency is discussed. To the author's knowledge, this is the first reported MPPC between pulsed and cw laser beams.