\left(
\delta_{\gamma\alpha}-\underline{\tilde{\chi}}^m_{\gamma\alpha}(\vec{k},s)\right)-
\frac{s^2}{c^2}\left(\delta_{ij}+\underline{\tilde{\chi}}^e_{ij}(\vec{k},s)\right)\right]\nonumber\\\end{aligned}$$ where it should be summed on the indices $ \alpha,\beta , \gamma
,\delta $ in the first term in the bracket. For a general medium it may be impossible to solve Eq.(\[c45\]) exactly to obtain the Green function $ \underline{G} $. However one can use a suitable iteration method and find the Green function up to an arbitrary accuracy which may be useful for media with considerably weak polarizability. Let us write the tensor $ \underline{\Lambda}(\vec{k},\vec{q},s)$ as the sum of two parts $$\label{c49}
\underline{\Lambda}(\vec{k},\vec{q},s)=\underline{\Lambda}^{(0)}(\vec{k},\vec{q},s)+\underline{\Lambda}^{(1)}(\vec{k},\vec{q},s)$$ where $$\label{c50}
\underline{\Lambda}^{(0)}_{ij}(\vec{k},\vec{q},s)=\left(
k_ik_j-\delta_{ij}k^2-\frac{s^2}{c^2}\delta_{ij}\right)\delta(\vec{k}-\vec{q})\equiv
L(\vec{k},s)\delta(\vec{k}-\vec{q})$$ is the tensor $\Lambda $ in free space, that is when there is no medium and $$\label{c51}
\underline{\Lambda}^{(1)}_{ij}(\vec{k},\vec{q},s)=-\varepsilon_{i\delta\gamma}\varepsilon_{\alpha\beta
j}k_\delta q_\beta
\underline{\tilde{\chi}}^m_{\gamma\alpha}(\vec{k},\vec{q},s)-\frac{s^2}{c^2}\underline{\tilde{\chi}}^e_{ij}(\vec{k},\vec{q},s)$$ is the part due to the presence of the medium, that is the effect of the medium in the total tensor $\Lambda $. Then, following the Born approximation method previously used in the scattering theory [@23], the Green function $\underline{G}$ can be expressed as a series as follows $$\label{c52}
\underline{G}(\vec{k},\vec{p},s)=\underline{G}^{(0)}(\vec{k},\vec{p},s)+\underline{G}^{(1)}(\vec{k},\vec{p},s)
+ \underline{G}^{(2)}(\vec{k},\vec{p},s)+\ \cdots\$$ where $$\label{c53}
\underline{G}^{(0)}(\vec{k},\vec{p},s)=L^{-1}(\vec{k},s)\
\delta(\vec{k}-\vec{p})$$ is the Green function for the free space and $
\underline{G}^{(n)}(\vec{k},\vec{p},s)\hspace{00.50
cm}n=1,2,3\cdots $ are found from the following recurrence relation $$\begin{aligned}
\label{c54}
&&\int d^3q \ \underline{\Lambda}^{(0)}(\vec{k},\vec{q},s)\ \cdot\
\underline{G}^{(n)}(\vec{q}, \vec{p},s)= -\int 