Viscosity measurement with laser-generated and detected shear waves

A technique is described in which laser-generated shear waves can be used to measure the viscosity of liquids. The technique involves measuring the shear wave reflection coefficient at a solid-liquid interface. To accommodate this procedure, a wedge was designed to launch laser-generated shear waves into the material at nearly normal incidence to the solid-liquid interface. The reflected laser-generated shear waves are detected at a second interface with a laser interferometer. The angle of incidence at this second interface is at an angle greater than the critical angle. The purpose of this arrangement is to maximize the out-of-plane displacement at this second interface so that detection with the interferometer can be more easily accomplished. Calculations that support the design of the wedge and experiment are outlined and experimental results are presented and discussed. This technique would be most applicable in those situations in which conventional techniques are not suitable, such as those involving high temperature and hostile environments. (C) 1999 Acoustical Society of America. [S0001-4966(99)03803-5].