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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 in the local temperature. Due to thermal effects, displacements occur in the medium, which can then propagate as elastic waves. Elastic waves within a bulk can be separated into two components: compression waves, corresponding to a curl-free propagation, and shear waves, corresponding to a divergence-free propagation \cite{aki2002quantitative}. Notably, measures of the transmission characteristics of  compression and shear waves are useful for inspecting solids, such as a 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; at this frequency, shear waves are quickly attenuated in soft tissue, tissues,  typically over a few microns, and only compression waves can propagate over a few centimeters. While the induction of surface acoustic waves by laser in soft tissues was recently demonstrated by Li et al. \cite{Li_2012}, \cite{Li_2014}, a similar phenomenon with shear waves in bulk medium  has never been described. This is of great interest for the development of laser-based shear wave elastography techniques. As its names name  indicates, shear wave elastography 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 so that their propagation can be observed over a few centimeters. In this article, we study the generation of shear waves by a laser beam in a soft medium. We theoretically describe the resulting two regimes 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 in Figure \ref{Figure1}, we used a Q-switch Nd:YAG laser (EverGreen 200, Quantel, Les Ulis, France) to produce a 10-ns pulse of 10 to 200 mJ energy at a central wavelength of 532 nm in a 5-mm diameter circular beam. The laser beam was absorbed in a 4x8x8 cm$^3$ tissue-mimicking black mat phantom composed of water, 5\% polyvinyl alcohol, and 1 \% black graphite powder. Two 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 ultrasonic probe, consisting of 128 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; tracking the speckle spots with an optical flow technique (Lucas-Kanade method with a 64x5-pixel window) window \cite{lucas1981iterative})  allowed for the computation of displacement displacements  along the Z axis (also defined as the ultrasound axis). Displacements over time were then filtered from 200 to 800 Hz using a 5th-order Butterworth filter and averaged over four experiments.