deletions | additions       diff --git a/Physical model.tex b/Physical model.tex  index db74da9..cd286c7 100644  --- a/Physical model.tex  +++ b/Physical model.tex 
...
I(z)=(1-R) I_0 \exp(- \gamma z)  \label{eq:expontentialDecay}  \end{equation}  where $R$ is the reflection coefficient of the material (supposed negligible on a black mat material as the one used here) and $\gamma$ the absorption coefficient of the medium. The absorption coefficient $\gamma$ can be estimatedin two ways: by measuring the fraction of light going  throughdifferent thickness of the medium or by calculating  the skin depth $\delta = \frac{2}{\gamma}$ (the $\delta$:  \begin{equation}  \gamma=\frac{2}{\delta}=2(\pi \sigma \mu_r \mu_0 \nu)^{\frac{1}{2}}  \label{eq:skinDepth}  \end{equation}  where $\sigma$ is the electrical conductivity of the medium, $\mu_r \mu_0$ its permeability, $\nu$ the frequency of the radiation and  factor 2 is dueto  the fact that relation of  $\delta$ is related to with  magnitude of the electrical field while $\gamma$ is related to the magnitude of the optical energy, which is equal to  the square of the electrical field magnitude). Skin depth $\delta$ is equal to $(\pi \sigma \mu_r \mu_0 \nu)^{-\frac{1}{2}}$, where $\sigma$ is the electrical conductivity of the medium, $\mu_r \mu_0$ its permeability and $\nu$ the frequency of the radiation. magnitude.  Substituting $\sigma \approx$ 0.1 S.m$^{-1}$, $\mu_r \mu_0$ = 4 $\pi \times 10^{-7} H.m^{-1}$ 10^{-7}$ H.m$^{-1}$  and $\nu$ = 3 10$^8$ / 532 10$^{-9}$ = 5.6 10$^{14}$ Hz, the skin depth for our medium is about 70 $\mu$m: it means that about 63\% of the radiation energy is absorbed in the first 70 micrometers of the sample. We have validated experimentally this value by measuring the fraction of light which go through different thicknesses of the medium (respectively 0, 30, 50 and 100 $\mu$m) with a laser beam power measurement device (QE50LP-S-MB-D0 energy detector, Gentec, Qu\'ebec, QC, Canada). We found respective transmitted powers of 100\%, 88\%, 71\% and 57\%, as illustrated in the Figure \ref{figAbsorpExp}. An exponential fit indicated that $\gamma^{-1} \approx$ 50 $\mu m$ in our sample.