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When a laser beam of sufficient energy is incident on a medium, the absorption of the electromagnetic radiation leads to an increase of in  the local temperature. Due to thermal effects, displacements occur in the medium. These displacements medium, which  can then propagate as elastic waves. Elastic waves within a bulk  can be separated into two components in a bulk: components:  compression waves, corresponding to a curl-free propagation; propagation,  and shear waves, corresponding to a divergence-free propagation \cite{aki2002quantitative}. Measures Notably, measures  of the compression and shear waves arenotably  useful for inspecting solids solids,  such as a metal metal,  to reveal potential cracks or defects \cite{Shan_1993}. In biological tissues, induction of compression waves by laser has been studied with the development of photoacoustic imaging \cite{Xu_2006}, \cite{22442475}. Elastic waves used in photoacoustic imaging are typically of a few megahertz: megahertz;  at this frequency,in a soft tissue,  shear waves are quickly attenuated, attenuated in soft tissue,  typically over a few microns, and only compression waves can propagate over a few centimeters. However, While the  induction of shear surface acoustic  waves by laser in soft medium has never been shown - most relevent work has been done tissues was  recently demonstrated  by Li et al.about the induction of surface acoustic waves by laser in soft tissues  \cite{Li_2012}, \cite{Li_2014}. \cite{Li_2014}, a similar phenomenon with shear waves has never been described.  This would yet be is  of high great  interest for the development of laser-based shear wave elastography techniques. As its names indicates, shear wave elastography covers comprises  the techniques used to map the elastic properties of soft tissues using shear wave propagation \cite{Plewes_1995}, \cite{muthupillai1995magnetic}, \cite{Catheline_1999}. These techniques typically use low frequency (50-500 Hz) shear waves to observe so that  their propagation can be observed  over a few centimeters. In this article, we studythus  the generation of shear waves by a laser beam in a soft medium. Wedescribe  theoretically describe  the resulting  two regimes occurring observed to occur  at different laser energies. We then propose a physical model to describe the observed phenomena, which is compared quantitatively and qualitatively with the experimental results. In our experiment, illustrated by in  Figure \ref{Figure1}, we used  a Q-switch Nd:YAG laser (EverGreen 200, Quantel, Les Ulis, France) produced to produce  a 10 ns 10-ns  pulse of 10 to 200 mJ energy at a central wavelength of 532 nm in a 5 mm 5-mm  diameter circular beam. The laser beam was absorbed in a 4x8x8 cm$^3$ tissue-mimicking black mat phantom made composed  of water, 5\% polyvinyl alcohol alcohol,  and 1 \% black graphite powder. Two freezing/thawing freeze/thaw  cycles were applied to stiffen the material to a value of 25$\pm$5 kPa \cite{17375819}. To observe the resulting shear waves, the medium was scanned simultaneously with a 5 MHz 5-MHz  ultrasonic probe made probe, consisting  of 128 elements elements,  connected to a multi-channeled ultrasound scanner (Verasonics V-1, Redmond, WA, USA). The probe was used in ultrafast mode \cite{bercoff2004supersonic}, acquiring 4000 ultrasound images per second during 30 ms. Due to the presence of graphite particles, the medium presented a speckle pattern on the ultrasound image: image;  tracking the speckle spots with an optical flow technique (Lucas-Kanade method with a 64x5 pixels 64x5-pixel  window) enabled to compute allowed for the computation of  displacement along the Z axis (also defined as the  ultrasound axis. axis).  Displacements along over  time were finally then  filtered from 200 to 800 Hz using a 5th order 5th-order  Butterworth filter and averaged over four experiments.