Experiment and theory on diffraction from laser-induced phase-hole in polymer film

Concentric diffraction rings with bright center in the far field and dark center in the near field of the probe beam were experimentally observed when a strong pump laser beam (526 nm) and a weak probe laser beam (632.8 nm) cross under the nonlinear medium film (Polypyrrylarylenemethine/polyvinyl film). Based on Fresnel-Kirchhoff diffraction integral equation, this phenomenon can be explained by the diffraction effect of the probe beam from the laser-induced phase-hole in the nonlinear medium caused by the pump beam. The numeric calculations give good agreement with the experimental results.