Self-pumped phase conjugation of laser beams in a nematic liquid-crystal layer with nonreciprocal feedback

A study is reported of self-pumped phase conjugation by near-forward stimulated scattering of a beam from a quasi-cw YAG:Nd laser in a layer of a nematic liquid crystal without an absorbing dye but in the presence of a nonreciprocal feedback loop. The phase nonreciprocity of this loop is realised by a polarisation rotator and a phase plate. A significant reduction in the threshold of generation of a phase-conjugated wave is reported for the case of a π/2 phase shift between the optical pump and scattering waves travelling in opposite directions along the feedback loop.