2004 Volume 73 Issue 6 Pages 732-740
The use of acoustic pulses to image materials is well-known in echography or sonar applications. We are extending this field by exploring the possibilities of generating very high frequency sound pulses on surfaces with ultrashort laser pulses and imaging the propagation in real time. To see the tiny vibrations produced on the sample surface, smaller than the dimensions of a single atom in amplitude, we use another set of laser pulses for scanned probing. The typical surface phonon wavelength produced is of the order of a few microns with frequencies up to 1 GHz. With such a system we can watch coherent phonon wave packets in two dimensions rippling across crystal surfaces and microscopic landscapes.
