FRACTAL SPECKLES

Speckle patterns having fractal properties were generated experimental ly by illuminating an ordinary diffuser with speckles produced in the Fraunhofer diffraction region of random fractal objects. The fractalit y of the speckle patterns manifested itself by the clustered appearanc e of intensities without any definite speckle size and was confirmed f rom a power law in intensity correlation functions. The size of the in tensity clusters and the exponent of the power-law in correlation func tions were studied as a function of the fractal dimension of the first object. Despite the fractality of the speckles, the probability densi ty of intensities was found to follow a negative exponential function. For comparison, three additional configurations using circular and ri ng-slit apertures were employed instead of the fractal objects. The pr operties of intensity correlations for these configurations were discu ssed on the basis of the properties of the illumination function over the diffuser, and the reason for the presence and absence of fractalit y in speckle patterns due to various optical conditions was elucidated . (C) 1998 Elsevier Science B.V. All rights reserved.