Laser heterodyne correlation processing of optical thickness irregularities in transparencies.
Irregularities in optical thickness of a given nondiffuse transparency are statistically inferred using optical heterodyne detection techniques. The modulus and phase of its complex amplitude transmittance can be recovered from a beat photocurrent by rotating the transparency in a signal laser beam. The ensemble averaged autocorrelation of the transmittance is obtained by making correlation measurements of the recovered real and imaginary parts of the transmittance. This autocorrelation function has a nonvanishing imaginary part, so that the spatial spectral profile (i.e., its power spectrum) of the transparency becomes asymmetric.
Ohtsuka
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Imai
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