Measurement of flow vorticity with helical beams of light

Abstract

It is possible to devise an experiment in which the local vorticity of a flow can be estimated by probing the fluid with Laguerre–Gauss (LG) beams, i.e., optical beams that show an azimuthal phase variation that is the origin of its characteristic nonzero orbital angular momentum. The key point is to make use of the transversal Doppler effect of the returned signal that depends only on the azimuthal component of the flow velocity along the ring-shaped observation beam. We found from a detailed analysis of the experimental method that probing the fluid with LG beams is an effective and simple sensing technique that is able to produce accurate estimates of flow vorticity.