Nonlinear optical phase conjugation by degenerate four-wave mixing (DFWM) is an important technique with applications in many fields of science and technology. Phase conjugation by Degenerate four-wave mixing is observed in Disperse Orange-25 dye doped in Polymethyl methacrylate – metacrylic acid (PMMA-MA) polymer film 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 and forward pump beam is 7 degrees. The effects of dye concentration, intensity of backward, forward pump and inter beam angle between probe and forward pump beam on phase conjugation reflectivity are also studied. PC signal strength first increases and then decreases. PC reflectivity is increased by increasing the intensity of the backward and forward pump beam. The polarization and intensity profile are verified to be preserved in the conjugate signal. The predominant phase conjugation signal is attributed to the facts that reverse saturable absorption and large third order susceptibility of the dye molecules.
Degenerate four-wave mixing and phase conjugation in a collisional plasma