deletions | additions       diff --git a/Introduction.tex b/Introduction.tex  index 388cfd7..d8985c1 100644  --- a/Introduction.tex  +++ b/Introduction.tex 
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In this study, we show that shear waves can be induced in soft tissues by a laser beam. We also propose a model for the underlying physical phenomenon. We finally applied the technique in a biological tissue to evaluate its potential application in shear wave elastography.  In the first experiment, illustrated by Figure \ref{Figure1}, we used a laser beam emitted by a Q-switch  Nd:YAG laser (EverGreen 200, Quantel, Les Ulis, France), which produced aQ-switched  pulse of energy $E$ = 200 mJ at a central wavelength of 532 nm during 20 ns in a beam of section $S$=20 mm$^2$. We defined Z as the laser beam axis, and the laser beam impact on the medium is the origin of coordinates (0,0,0). The laser beam was absorbed in a 4x8x8 cm$^3$ tissue-mimicking phantom made of water and of 5\% polyvinyl alcohol, 1 \% black graphite powder and 1\% salt. A freezing/thawing cycle was applied to stiffen the material to a value of 15$\pm$5 kPa \cite{17375819}. The laser is absorbed in the medium with an exponential decay of the optical intensity $I(z)=I_0 \exp(- \gamma z)$ along medium depth $z$, where $I_0=\frac{1}{S}\frac{d E}{dt}$ is the incident intensity distribution at the surface (the reflection on the black mat medium being neglected) and $\gamma$ the absorption coefficient of the medium.  !!!We measured the fraction of light which go through different thicknesses of the medium with a laser beam power measurement device (): it indicated that $\gamma \approx$ ??? m$^{-1}$ in our sample,!!! meaning that most of the radiation is absorbed in the first hundred of micrometers. 
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