From Speckles to Modes: Principles and Applications of Fiber Optic Dynamic Light Scattering

Abstract

The instrumentation of Dynamic Light Scattering (DLS) is undergoing a small revolution: the classical pair of pinholes, whose role is to select a single speckle, is being replaced by single-mode fibers that select a single mode. This improves the performance of the apparatus substantially, but the improvement is also accompanied by a sad loss: the visible (and beautiful) boiling speckle pattern is replaced by the seemingly abstract notion of receiver mode. In my lecture I will introduce the principles of modeselective optical receivers, discuss the relation of modes with speckles and show that it is worthwhile to accept this slight change of the point of view. The gain is a considerable simplification of the instrumentation as well as of the theoretical reasoning. This enables the researcher to tackle, more easily, difficult experimental problems such as the in vivo DLS in human eye vitreous or the motion of colloidal particles in opaque porous media.