Spatial phase filtering based on the intensity-dependent refractive index of PbS nanocomposite film

We demonstrate the use of stable films containing PbS nanocrystals as media for self-adaptive phase filtering in phase contrast imaging of transparent objects by a cost-effective exploitation of nonlinear optical refraction in a simple, all-optical, and self-adjusting 4f imaging system. The optical nonlinearity is characterized by z-scan technique using a continuous wave He-Ne laser as the excitation source. The mechanism of nonlinearity in this case is mainly due to the nonlocal thermo-optical interaction between the laser beam and the sample. The value of nonlinear refractive index coefficient is found to be -3.5x10(-7) cm(2)/W. The nanocomposite material shows a thermal lens effect and is a potential candidate for phase contrast imaging.