Production of pico and
subpicosecond optoacoustic pulses
A. N. Dharamsi
Department of
Electrical and Computer Engineering, Old Dominion University Norfolk, Virginia
23529
A. B. Hassam
Department of Physics and Astronomy University of Maryland, College Park, Maryland 20742
A method for generating pico- and subpicosecond optoacoustic pulses is discussed.
The physical mechanism is based upon the phenomenon of “electronic expansion”
(or photostriction) in which the lattice constant of a solid changes upon the
creation of electron— hole pairs. Acoustic signals generated by this mechanism
would be up to an order of magnitude shorter than those generated by other
schemes currently in use. An expression for the acoustic compression expected
in this method is derived. It is shown that the nonthermal nature of the
phenomenon, in conjunction with the band structure of materials exhibiting gaps
between conduction bands, can be exploited to obtain ultrashort optoacoustic
pulses that have no thermoelastic components. A comparison of the thermoelastic
and nonthermal photostrictive mechanisms is made.
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