Abstract
We propose a defect-enhancement system for periodic patterns using a nonlinear spatial filter that uses photoinduced anisotropy of a bacteriorhodopsin film. The nonlinear filter passes low-intensity beams while blocking high-intensity beams. The system enhances the defects in real time because the anisotropy induced on the bacteriorhodopsin film by the first sample does not have to be rewritten if subsequent samples have the same periodic structure. It can also be applied to moving samples due to the shift invariance of the Fourier pattern. In the experiments we detected 10 µm defects in a photomask for a liquid crystal display. The dependence of the contrast ratio of the enhanced defect to the background on the intensity of the probe beam is also measured.
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