Real-time enhancement of defects in a periodic mask using photorefractive Bi_12SiO_20

The first known experimental results of real-time optical defect enhancement of a periodic mask are reported. A low-intensity reference wave interferes with the Fourier transform of an object beam to form a hologram in a photorefractive crystal. The nonlinear properties of the crystal perform a filtering operation, and phase-conjugate readout results in a defect-enhanced image. Defects of size 10 microm x 100 microm have been easily detected with high signalto- noise ratio, and a discussion of performance limitations is presented.