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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 the local temperature. Due to thermal effects, displacements occur in the medium. These displacements can then propagate as elastic waves. Elastic waves are separated in two components in a bulk: compression waves, corresponding to a curl-free propagation; and shear waves, corresponding to a divergence-free propagation \cite{aki2002quantitative}. Measures of the compression and shear waves is are  notably used as a method of inspection to reveal potential cracks in a solid useful for inspecting solids  such as a metal. metal and revealing potential cracks.  In a medical context, 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, in a soft tissue, shear waves are quickly attenuated, typically over a few microns, and only compression waves can propagate over a few centimeters.   In the other hand, shear waves have drawn an increasing interest in medical imaging, with the development of shear wave elastography techniques for the last two decades \cite{muthupillai1995magnetic}, \cite{sandrin2002shear}. As its names indicates, this term covers the techniques used to measure or map the elastic properties of soft tissues using shear wave propagation. They typically use low frequency (50-500 Hz) shear waves because they can be observed over a small distance. However, it has not been demonstrated until now that a laser could be able to generate low frequency shear waves in soft medium.  In this study, article,  we study thus  the induction generation  of shear waves by a laser beam in a soft medium. We have been able to distinguish describe theoretically the  twodifferent  regimes depending on occurring at different  laser energy. energies.  We propose then  a physical model to describe the observed phenomenons. phenomena, which is compared quantitatively and qualitatively with the experimental results.  In the first our  experiment, illustrated by Figure \ref{Figure1},we used  a Q-switch Nd:YAG laser (EverGreen 200, Quantel, Les Ulis, France), which France)  produced a 10 ns  pulse of energy $E$ = 10 to  200 mJ energy  at a central wavelength of 532 nmduring 10 ns  in a 5 mm diameter circular beam.Z is defined here as the laser beam axis and origin of coordinates (0,0,0) as the laser impact location on the medium.  The laser beam was absorbed in a 4x8x8 cm$^3$ tissue-mimicking black mat phantom made of water and of 5\% polyvinyl alcohol and 1 \% black graphite powder. A Two  freezing/thawing cycle was cycles were  applied to stiffen the material to a value of 15$\pm$5 25$\pm$5  kPa \cite{17375819}. To observe the resulting shear waves, the medium was scanned simultaneously  with a 5 MHz ultrasonic probe made of 128 elements connected to a Verasonics 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 image: tracking  the speckle spots with an optical flow technique (Lucas-Kanade method with a 64x5 pixels window) allowed enabled  to computeZ-axis component of the  displacement in the medium. along ultrasound axis.  Displacements along time were then filtered from 200 to 800 Hz using a 5th order Butterworth filter.