Volumetric speckles: examination of the 3D form of speckles in free space and Fourier transforming systems

Speckles are a statistical interference phenomenon which arises when coherent light is scattered by an optically rough surface. The resulting speckle field can be examined using statistical techniques and some results that arise are related to the form of the resulting speckles. Characteristic features are the so-called lateral and longitudinal speckle size as well as the orientation of speckles in the z-direction. It has been shown that the 3D orientation of speckles in free-space and in Fourier transforming systems are different from each other. Here we review some of Sheridan's work in this area. We first examine the speckle field formed by a diffuser in free space over a 3D volume. Next an Optical Fourier Transform (OFT) system is assumed, where the diffuser is placed in the front focal length of a Fourier transforming lens and we examine the resulting speckle field in the back focal plane of this OFT system. We compare and contrast the properties of the speckles from both setups free-space and Fourier.