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For elastography measurements, Muthupillai et al. assumed that a displacement of a few hundreds of nanometers should be sufficient to perform shear wave elastography \cite{7569924}. However, displacements of 5 to 20 $\mu$m are usually required, which is slightly higher than the maximum displacement observed here (about 2 $\mu$m in the chicken breast sample). The maximum minimum  energy of the laser (532 nm, 10 ns, 200 50  mJ, 5 mm diameter) used in our experiments to get a shear wave  is about fifty ten  times higher than the maximum exposure permissible as given by the current American National Standard Institute (Z136.1-2000) for skin \cite{ANSIZ1361}, but is also about five fifty  to ten hundred  times lower than the typical energy used for skin tatoo removal \cite{8352621}.More efficient displacement observation methods could be performed with better displacement tracking algorithms and devices with a higher spatial resolution, such as ultrasound transducer of higher frequency or an optical coherence tomography probe.  Shear wave frequency in elastography ranges typically between 50 and 500 Hz, with higher frequency meaning better spatial resolution. The experiments demonstrated that these frequencies can be reached, although the mechanism explaining this particular frequency is not clear yet. 
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