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Abstract |
Propagation and Diffraction of
Picosecond Acoustic Wave Packets in the Soliton Regime
O.L.Muskens, J.I.Dijkhuis (Atom Optics
and Ultrafast Dynamics, Debye Institute, University of Utrecht, Utrecht, the
Netherlands)
e-mail:
O.L.Muskens@phys.uu.nl
Recent
experiments on nonlinear propagation of picosecond acoustic wave packets in
condensed matter have opened up a new, exciting area of soliton physics. Single
cycle strain pulses as short as several picoseconds can be generated in a thin
metallic film, yielding local strain fields exceeding 10-4. The combination of
phonon dispersion and anharmonicity of the atomic interaction potentials may
give rise to strongly nonlinear, but stable propagation of the wave packets
over a distance of the order of several millimeters in a single crystalline
material. We present new results on nonlinear propagation of acoustic wave
packets created by nJ, femtosecond optical pulses in lead molybdate and
sapphire single crystals, employing the Brillouin scattering technique as a
local probe of acoustic strain. Studies of diffraction of narrow discs of
acoustic strain show anomalous diffraction of the various Fourier components of
the wave packet. Propagation of virtually one-dimensional nature is studied by
exciting the metal film over a large area using mJ optical pulses from an
amplified femtosecond laser. In this regime a strong, coherent redistribution
of acoustic energy over the wave packet spectrum is observed, which is a clear
indication for the formation of acoustic solitons.
Section
: 2