Abstract

When an isolated circular defect on an otherwise very smooth reflective surface is illuminated at normal incidence by coherent parallel light, a Fraunhofer diffraction pattern from the defect can be observed in the transverse plane in which a lens focuses the light retroreflected from a defect-free surface. The ratio of the intensity when the defect is illuminated to the intensity in the absence of the defect vs distance r from the center of the focused light spot exhibits a maximum at some distance r = r_m in the interval 0 < r < r_{1 min}, where r_{1 min} is the radius of the central bright spot in the defect diffraction pattern. On the basis of Fraunhofer diffraction, a relation was derived from which the diameter of the defect can be calculated by substituting in the measured distance r_m at which the ratio of intensity when the defect is present to the intensity from a defect-free surface is a maximum. Experimental data were obtained verifying the theory.

© 1980 Optical Society of America

Normalization of the scattered light from a defect illuminated by a Gaussian beam

Paul E. Klingsporn
Appl. Opt. 19(2) 313-318 (1980)

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Measurement of size and concentration of scattering particles by speckle photography

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