Broadband photorefractive phase conjugation in a dispersive scheme

Degenerative wave mixing in photorefractive (PR) crystals is suitable for t he elimination of wavefront distortions and for beam cleaning; however, tra ditional schemes are restricted to monochromatic light sources of macroscop ic coherence length. We report on experimental results which demonstrate th at our novel disperse arrangement is well suited to PR phase conjugation of broadband radiation emitted by cw and femtosecond lasers. The efficiency o f the wave mixing process depends on the contrast and length of the index g rating produced in the PR crystal. In order to improve the efficiency we di sperse the broadband laser beam perpendicular to the plane of propagation b y a diffraction grating. The different spectral components appear spatially decomposed in the focal plane of a cylindrical lens, where the PR crystal is placed. We review our results in the cw regime and, for the first time, we report on experiments with femtosecond pulses, too. The PR crystal was a n undoped BaTiO3 used in "CAT" self-pumped phase conjugation configuration. The light sources were Ti-sapphire lasers. The performance of the novel sc heme was investigated in different conditions, and we observed efficient PC up to tens of nanometers of spectral bandwidth.