Measuring laser-speckle statistics in scaled-laboratory experiments

Abstract

Generating fully developed speckle in a repeatable way is of interest to ongoing scaled-laboratory experiments. Such experiments often look to validate theoretical and numerical predictions for numerous laser-based applications. Unfortunately, experimental constraints such as camera-pixel sampling, residual-sensor noise, and cover-glass etaloning limit one’s ability to match the statistics of fully formed speckle in a straightforward way. In this paper, we develop expressions for the speckle probability density function (PDF) and speckle contrast, which account for the effects of camera-pixel sampling (relative to the size of the speckles), as well as Gaussian-distributed additive noise. We validate these expressions using wave-optics simulations, which also account for the separate effects of cover-glass etaloning. Next, we set up an experiment that limits the effects of the cover-glass etaloning (as much as possible). The results show excellent agreement with the expressions we develop for the speckle PDF and speckle contrast. This agreement will enable future scaled-laboratory experiments to match the statistics of fully developed speckle in a straightforward way.