Ultrasonic experiments at ultra-high frequency with picosecond time-resolution

A method that can be used to make ultrasonic measurements with picosecond time resolution is described. In this method, short light pulses (duration ⩽1 ps) are used to generate and detect ultrasonic waves. The excellent time resolution makes possible pulse-echo ultrasonic measurements in situations in which the acoustic path length is extremely short. It is possible to make ultrasonic pulse-echo measurements on thin-film microstructures of thicknesses down to a few hundred angstroms. As examples of the use of the method, measurements of sound propagation in glass films at frequencies up to 500 GHz, studies of the mechanical properties of microstructures, and investigations of high-frequency surface waves are described