INTERACTION OF LIGHT WITH A TRANSVERSELY MOVING NONLINEAR MEDIUM - BEYOND DOPPLER-LASER-VELOCIMETRY

Interaction of a laser beam with a transversely moving nonlinear mediu m has been studied both experimentally and theoretically. With the mes ophase of a nematic Liquid crystal (NLC) as the nonlinear medium, tran sverse motion of the NLC at speeds of similar to 1 mu m/s relative to the laser beam, causes remarkable changes in its orientational state. The response of the medium to the transverse motion is enhanced consid erably in the case of threshold nonlinearity where the reorientation o f the LC takes place as a second order phase transition. The diffusive transport of light induced perturbations of the nonlinear medium, giv e rise to a far field projection pattern that consist of a system of c oncentric arcs. The observed phenomena can lead to potential applicati ons for measurement or visual sensing of motion. Alternatively it can provide a means for the characterization of nonlinear materials. (C) 1 998 American Institute of Physics.