deletions | additions       diff --git a/When_a_laser_beam_of__1.tex b/When_a_laser_beam_of__1.tex  index 06d1a3c..0168fdd 100644  --- a/When_a_laser_beam_of__1.tex  +++ b/When_a_laser_beam_of__1.tex 
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I=I_0 \exp(- \gamma z)  \end{equation}  where $I_0$ is the incident intensity distribution at the surface and $\gamma$ is the absorption coefficient of the medium. In non-metallic solids, the absorption coefficient $\gamma$ is relatively small, so that the radiation is able to penetrate into the bulk of the material - contrary to metals where the radiation is absorbed within a few nanometres. The absorption of the laser beam by the medium gives then rise to an absorbed optical energy $q$ equal to $\gamma I$.  Assuming that all the optical energy is converted to heat, a local increase of temperature appears. Temperature distribution $T(x,y,z,t)$ can be computed using heat equation \cite{Li_2014}: equation:  \begin{equation}  \frac{\partial T}{\partial t} = \frac{k}{\rho C} \nabla ^2 T + \frac{q}{\rho C}  \end{equation} 
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