Information inferred from the observation of speckles

Speckle is the peculiar appearance acquired by a diffusion object when illuminated by a laser beam. A laser-illuminated surface gives rise to a randomly distributed amplitude in any plane parallel to its plane. The real and imaginary parts of the amplitude at any point of the plane under consideration have zero mean value and the contrast of the speckle pattern is maximum. The autocorrelation function of the intensity distribution is proportional to the Fourier transform of the aperture limiting the surface, and the average size of a speckle in the considered plane is given by the radius of its Fraunhofer diffraction pattern. The results are applied to the optical processing of information, to speckle photography and to speckle interferometry.