Abstract
Above-band-gap picosecond pulses are used to generate holographically high-frequency, coherent, surface acoustic modes on semiconductor surfaces. Optical diffraction from the surface acoustics is in superposition to a free-carrier phase grating that acts as an amplifying cross term in the diffraction process. The detection limits are of the order of 10−4 nm for the surface displacement. Frequencies up to 2 GHz have been realized, with frequencies >20 GHz possible. A quantitative theory for the photothermal coupling has been developed. In addition, propagation of the optically generated surface modes has revealed a solid–liquid phase transition of the water layer at TiO2–H2O interfaces.
© 1988 Optical Society of America
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