Interaction of light with a transversely moving nonlinear medium: Beyond Doppler laser velocimetry

Abstract

Interaction of a laser beam with a transversely moving nonlinear medium has been studied both experimentally and theoretically. With the mesophase of a nematic liquid crystal (NLC) as the nonlinear medium, transverse motion of the NLC at speeds of ∼1 μm/s relative to the laser beam, causes remarkable changes in its orientational state. The response of the medium to the transverse motion is enhanced considerably in the case of threshold nonlinearity where the reorientation of the LC takes place as a second order phase transition. The diffusive transport of light induced perturbations of the nonlinear medium, give rise to a far field projection pattern that consist of a system of concentric arcs. The observed phenomena can lead to potential applications for measurement or visual sensing of motion. Alternatively it can provide a means for the characterization of nonlinear materials.