UV laser excited surface acoustic waves - quantitative measurements and comparison with theory

Summary form only given. Laser excitation and detection of acoustic waves is a powerful tool for investigating material properties. In order for acoustics to be useful in industrial settings, large amplitude deflections of several nanometers are required to be clearly visible, above background noise. Previous studies using infrared Nd:YAG laser pulses have indicated that surface acoustic wave amplitudes of 2 nm peak to peak and 8 nm peak to peak can be excited at distances of 10 mm and 7 mm respectively with laser energies of 80 mJ and 30 mJ respectively. Thus there appears, to be differences in the measured wave amplitudes in the previous studies. We expect that UV laser pulses which suffer less plasma shielding from air breakdown and generate higher ablation pressures due to, coupling to higher plasma densities are capable of generating larger amplitude acoustic waves than infrared, laser pulses. A full study is being carried out of the ablative excitation, of surface acoustic waves in order to determine such parameters as magnitude and shape of the, acoustic wave and the velocity at which the wave, propagates. Few quantitative studies of the amplitude and shape of the surface acoustic wave have been reported to date and all of these have been for visible or infrared pulse excitation.