  The use of femtosecond laser pulses to impulsively excite thermal and
mechanical transients in matter has led, in the last years, to the development
of picosecond acoustics. Recently, the pump-probe approach has been applied to
nano-engineered materials to optically generate and detect acoustic waves in
the GHz-THz frequency range. In this paper, we review the latest advances on
ultrafast generation and detection of thermal gradients and pseudo-surface
acoustic waves in two-dimensional lattices of metallic nanostructures.
Comparing the experimental findings to the numeric analysis of the full
thermo-mechanical problem, these materials emerge as model systems to
investigate both the mechanical and thermal energy transfer at the nanoscale.
The sensitivity of the technique to the nanostructures mass and shape
variations, coupled to the phononic crystal properties of the lattices opens
the way to a variety of applications ranging from hypersonic waveguiding to
mass sensors with femtosecond time-resolution.ens the way to a variety of
applications ranging from hypersonic waveguiding to mass sensors with
femtosecond time-resolution.

Mesoscale and Nanoscale Physics;Materials Science