Azo dye-doped polymer films for optical limiting & Optical phase conjugation

Nonlinear optical properties, optical limiting and Optical phase conjugation through degenerate four-wave mixing is observed in Disperse Orange-25 dye-doped in Polymethyl methacrylate - metacrylic acid (PMMA-MA) polymer films under low-power, continuous-wave laser irradiation. A maximum phase conjugate efficiency of 0.22% has been obtained for probe beam intensity at 0.11 W/cm². Phase conjugation is observed for both parallel- and orthogonally-polarized probe and pump beams. The maximum PC reflectivity is achieved when the angle between probe beam and forward pump beam is 7 degrees. The effects of dye concentration, inter beam angle between probe and forward pump beam on phase conjugation reflectivity are also studied. PC signal strength first increases and then decreases with time. PC reflectivity is also increased by increasing the intensity of the backward and forward pump beam. The predominant phase conjugation signal is attributed to the facts that reverse saturable absorption and large third order susceptibility of the dye molecules.