Optical phase conjugation in methylene blue films

Optical phase conjugation in methylene blue sensitized gelatin film has been obtained with 514.5-nm radiation from an argon-ion laser with power levels as low as 50 mW/cm(2) for the pump beam in a degenerate four-wavemixing configuration. The film with a thickness of 110-120 microm prepared from a solution of a 1.8-mmol concentration of methylene blue sensitized gelatin shows a good phase-conjugate reflectivity of 0.5% for this power level at 514.5 nm, which is well away from its absorption peak at ~ 650 nm.