Physical properties of speckles

Speckles appear everywhere in space whenever an optically rough surface is illuminated with highly coherent light, however, of particular interest for practical purposes are the image and Fraunhofer diffraction planes. Schematic diagrams illustrating the formation of speckling in the Fraunhofer diffraction plane and in the image plane are discussed. Speckle pattern recorded in the Fraunhofer diffraction plane for coarse grained and fine grained ground glass plates are given, along with the frequency spectra of the corresponding surface roughnesses. It is shown how speckles have become a powerful and simple tool for studying surface roughnesses, for measuring displacement and strain, and for deformation and vibration analysis.