deletions | additions       diff --git a/When_a_laser_beam_of__1.tex b/When_a_laser_beam_of__1.tex  index f00433e..2ab4dbd 100644  --- a/When_a_laser_beam_of__1.tex  +++ b/When_a_laser_beam_of__1.tex 
...
In the thermoelastic expansion, a local dilatation of the medium occurs. In an unbounded solid, this would lead to a rotational-free displacement, so no shear wave would occur. However, in our case, the solid is rather semi-infinite. The local expansion acts as a dipole force parallel to the surface. In the ablative regime, the local increase of temperature is so high that the surface of the medium melts and creates a point-force in the medium. The medium is then displaced locally inside the medium along Z axis. At very high temperatures, even a plasma can occurs. The local force leads to compression and shear waves.  In both cases, the absorption of the laser by the phantom leads to a local displacement which can propagate as elastic wave in the medium. To observe the elastic wave, the medium was scanned with a 5 MHz ultrasonic probe made of 128 elements and a Verasonics scanner (Verasonics V-1, Redmond, WA, USA). The probe was used in ultrafast mode \cite{bercoff2004supersonic}, acquiring 1000 ultrasound frames per second. 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) allowed to compute one component of the displacement in the medium (``Z-displacement'' (\textit{Z-displacement}  or ``Y-displacement''). \textit{Y-displacement}).  The laser beam was triggered 10 ms after the beginning of the ultrasound acquisition.    
...