1255139

Merging nonlinear acoustics and nonlinear optics : laser generated intense acoustic pulses and breakdown in dielectrics

Christos Flytzanis
Ecole Normale Superieure, Laboratoire Pierre Aigrain, Paris, France


Nonlinear acoustics and nonlinear optics share some common features at the same time as they markedly differ in others. Both rely on anharmonic wave couplings but nature has been far more generous with acoustic anharmonicities than with optical ones and to such an extent that the nonlinear interactions and propagation of the former ones effectively appear as local while the later show predominantly nonlocal features.

This is strikingly evidenced in the vastly different space and time scales involved in the two classes of nonlinear wave generation and propagation and the underlying mechanisms. Precisely these differences in anharmonicity and nonlocality shape the opto-acoustic interactions as well and the amplitude-coherence transfers from the ones to the others, this being exclusively done from optical to acoustical.

Here we review the optoacoustic processes that lead to large amplitude acoustic phonon pulse generation in dielectrics using nonlinear electro-optical processes in the nanosecond-subpicosecond pulse regime.
We first consider the parametric generation of sound pulses without optical absorption losses and briefly review the use of coherent processes such as stimulated and impulsive Brillouin effects and phonon and polarization echos to develop nonlinear acoustic spectroscopy along the same lines as in nonlinear optical spectroscopy and obtain information about coupling constants of acoustic waves with other material excitations, relaxation processes and phase transitions in dielectrics.

We then consider the case of acoustic shock waves generated concomitant with breakdown and permanent lattice modifications in well confined spots in the dielectric intermediated through “hot spot” or plasma creation and subsequent phonon generation and avalanche through anharmonic couplings. The main steps leading to laser induced breakdown are assessed and analysed and some applications are briefly presented.


<< Back to page "Keynote Lectures"