Spectral compression of ultrafast acoustic transients in thin films for enhanced detectability

Experimental results showing the generation of ultrafast acoustic transient s in thin films demonstrate the production and use of an optical pulse trai n for excitation that enhances signal detectability. Results in an aluminum thin film on a tungsten-carbide substrate show generation and detection of a narrow-band acoustic signal centered at 32.34 GHz. It is shown that the signal-to-noise ratio of the recorded transient is improved by a factor of 1.7 when simple digital bandpass filtering at the center frequency is perfo rmed. The physical limitations of this approach are considered in order to assess conditions under which significant bandwidth reduction can be realiz ed. (C) 2001 American Institute of Physics.