Isolated detection of elastic waves driven by the momentum of light

Electromagnetic momentum carried by light is observable through the mechanical effects radiation pressure exerts on illuminated objects. Momentum conversion from electromagnetic fields to elastic waves within a solid object proceeds through a string of electrodynamic and elastodynamic phenomena, collectively bound by momentum and energy continuity. The details of this conversion predicted by theory have yet to be validated by experiments, as it is difficult to distinguish displacements driven by momentum from those driven by heating due to light absorption. Here, we have measured temporal variations of the surface displacements induced by laser pulses reflected from a solid dielectric mirror. Ab initio modelling of momentum flow describes the transfer of momentum from the electromagnetic field to the dielectric mirror, with subsequent creation/propagation of multicomponent elastic waves. Complete consistency between predictions and absolute measurements of surface displacements offers compelling evidence of elastic transients driven predominantly by the momentum of light

Generation and detection of thermoelastic waves in metals by a photothermal mirror method

We investigate the thermoelastic waves launched by a localized heat deposition. Pulsed laser excitation is used to generate mechanical perturbations in metals that are detected using the photothermal mirror method. This method detects the wavefront distortion of the probe beam reflected from the perturbed sample surface. Nanometer scale expansion of the material is induced just under the irradiated surface releasing transient thermoelastic waves of much smaller amplitudes on the surface. Numerical predictions and the experimental results are in a good agreement and represent both the thermal diffusion of the large amplitude, long-lasting outward bulge, and the released elastic waves

A 3-dimensional time-resolved photothermal deflection \u201cMirage\u201d method

A three-dimensional time-resolved theory and experiment for photothermal deflection spectroscopy is developed. The heat conduction equations for two semi-infinite media consisting of an opaque sample and a fluid are solved considering temperature and energy flux balance conditions for a Gaussian heat source. The time dependent perpendicular deflection signal is calculated and compared to experimental measurements on glassy carbon and copper samples. Excellent agreement with literature values for thermal diffusivity of the samples is found. The transient behavior is analyzed for different coupling fluids.Peer reviewed: YesNRC publication: Ye