ABSTRACT
Light from a diffusing surface illuminated by a laser beam exhibits a characteristic granularity called speckle pattern. The speckle affects amplitude of the scattered light, and also the phase of an interferometric measurement, leading to an error. This error shall be kept small, if we wish to replace the corner cube with a simple diffuser. This chapter introduces the description of speckle by means of a statistical treatment and the calculation of various quantities of interest in interferometric measurement, amplitude and its square (power), free (or unconditioned) phase, and phase conditioned to amplitude. Thereafter, the speckle phase error of vibration and displacement measurements is calculated and its impact on interferometric measurements on diffusing (i.e. non-specular) surfaces is analyzed and commented. A technique for alleviating the speckle error, based on tracking the maximum of speckle intensity is then developed. A short description of ESPI (electronic speckle pattern interferometry) is finally presented.
