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In the context of shear wave elastography, the thermoelastic regime is a priori preferred over the ablative regime, because it is not destructive. Even if first shear wave elastography experiments
\textcolor{red}{in biological tissues} assumed that a displacement of a few hundred nanometers would be sufficient \cite{7569924}, displacements of the order of a few micrometers are usually required in practice for ultrasound or magnetic resonance elastography
\textcolor{red}{in biological tissues} \cite{Nightingale_2001}, \cite{Manduca_2001}. Interestingly, this
amplitude is higher than the displacement we observed at 10 mJ (thermoelastic regime), but along the same order of magnitude of the displacement observed at 200 mJ (ablative regime). \textcolor{red}{For application in human body}, the lowest fluence \textcolor{red}{(500 J/m$^2$, corresponding to a 10 mJ, 5 mm-diameter laser beam)} that was used in these experiments is incidentally 2.5 times above the maximum permissible exposure for skin \textcolor{red}{(200 J/m$^2$)} given by the Z136.1-2007 standard of the American National Standard Institute \cite{ANSIZ1361}. To overcome this issue, different strategies could be adopted to comply to ANSI standard, including emission of the laser beam onto a protective absorbing layer, such as a black sheet covering the patient's \textcolor{red}{skin} \cite{Li_2014}. Alternatively, the medium could be observed with a high resolution imaging technique able to track displacements of a few nanometers, such as high frequency ($>$100 MHz) ultrasound imaging or optical coherence tomography \cite{Li_2011}. Combination with optical coherence tomography can even lead to a real-time, fully remote, small-scale laser-based technique to assess a medium elasticity.
In conclusion, we have presented experimental observations of elastic shear waves generated by a laser beam in a soft medium. The involved phenomena were investigated, and revealed the existence of thermoelastic and ablative regimes. Furthermore, theoretical displacements were in good agreement with experimental measurements. Lastly, numerical studies showed displacement propagation patterns that were comparable to those generated experimentally.