Generation and observation of GHz ultrasonic waves on liquid surfaces and a liquid/liquid interface by transient reflecting grating method

We optically generated and observed GHz ultrasonic waves on liquid surfaces and a liquid/liquid interface for the first time using the transient reflecting grating (TRG) method. Four kinds of samples were used for measurement of the surfaces; two types of black ink, an aqueous solution of crystal violet (CV aq solution) and ethanol aqueous solutions of CV. A cyclohexane/CV aq solution interface was used for measurement of the liquid/liquid interface. The 0.7 GHz and 0.6 GHz ultrasonic waves were generated on the liquid surfaces and the liquid/liquid interface, respectively. These ultrasonic waves resemble longitudinal acoustic waves partly localized at the surface, and they cause surface displacement. The amplitudes of TRG signals from surfaces of the CV mixed solvent solutions were found to be greatly affected by both the viscosity and surface tension. This result indicated the viscosity and interface tension must be considered as perturbations in the elastic theory. The strong dependence on interface tension showed the high selectivity of the TRG signals for the interface. (C) 1999 American Institute of Physics. [S0021-9606(99)70244-8].