CC BY
25LMI-I-13
Ultrafast-Laser generated nanoacoustic waves and their applications on material diagnosis
N. Papadogiannis1
1Hellenic Mediterranean University, Institute for Plasma Physics and Lasers, Rethymnon, Greece
When ultrafast laser pulses interact with the metallic thin-film transducer of a nanostructured composed material, the free electrons of the metal absorbs the laser photons and excited either in high energy states or in the continuum. Then, the overwhelming majority of the excited electrons transfer their excess energy in to the lattice or in to other electrons via non-radiative processes named electron-lattice and electron-phonon scattering. In later time localized high temperature and high pressure field is appeared in the interaction volume which generates a localized and fast moving mechanical nano-strain pulse outwards from the interaction region. Depending on the laser pulse characteristics and the nature of the materials involved in the process, different type of mechanical waves are generated and different physical phenomena occur. Above that, the phase of the material may change during the interaction process or during the mechanical wave propagation.
The physics and the applications of ultrafast-laser generated nanoacoustic waves on metal thin films transducers mounted on dielectric (or semiconductor) substrates will be presented for different laser pulse excitation characteristics. Both, Rayleigh-type surface mechanical waves, and longitudinal phononic acoustical strains propagated normally to the surface, will be explored. State of the art pump-probe experimental techniques based on whole field dynamic laser nano-imaging or degenerated transient reflectivity methods will be analyzed and discussed. Theoretical models that describe the laser-material interaction processes and the generation and propagation of mechanical waves for different laser characteristics and different materials seem to be validated. Finally, successful optical coherent control of nanostrains in semiconductor materials, of the lasergenerated mechanical waves will be shown using sophisticated initial electron excitation.
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