Optical surface inspection using real-time Fourier transform holography in photorefractives

We present real-time optical preprocessor intended to enhance small defects in a smooth surface. The heart of the system is a photorefractive Bi(12)SiO(20) phase-conjugate mirror which reflects only the low intensity features of the object's optical Fourier transform. By adjusting the beam ratios so that only the low intensity, high spatial frequency image components are phase conjugated and inverse transformed, an image consisting of just the defects is produced. To our knowledge, this is the first use of this technique on opaque and nonperiodic objects. We present experimental data showing enhancement of defects as small as 0.14 microm.