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\begin{displaymath} \tilde{n} = n + i \kappa, \ \ \ k= \tilde{n}\omega/c = (n+i\kappa )\omega/c \end{displaymath} (23)


$\displaystyle E(z,t)$ $\textstyle =$ $\displaystyle E_0 e^{i(kz-\omega t)} = E_0 e^{-\kappa \omega z/c} e^{i(n\omega z/c - \omega t)}$ (24)
$\displaystyle I$ $\textstyle \propto$ $\displaystyle E^* E = \vert E_0 \vert^2 e^{-\kappa \omega z/c} = I_0 e^{-\alpha z}$  
$\displaystyle \alpha$ $\textstyle =$ $\displaystyle 2 \kappa \omega /c$ (25)
$\displaystyle \tilde{n}^2$ $\textstyle =$ $\displaystyle \tilde{\epsilon } = \epsilon_1 + i\epsilon_2$ (26)
$\displaystyle \epsilon_1$ $\textstyle =$ $\displaystyle n^2 - \kappa^2, \ \ \ \epsilon_2 = 2 n\kappa$ (27)

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