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    {

    \def \l {\mathrm{l}}

    \def \r {\mathrm{r}}

    \def \Bl {\mathrm{Bl}}

    \def \Br {\mathrm{Br}}

    \def \B {\mathrm{B}}

    \def \nIIom {n_{2\omega}}

    \begin{equation}\label{eq:interface_conditions}

        \begin{aligned}

          F_{1\l} &= F_{2\r} + F_{2\l} \exp (i\,k_2 L) + F_{\Br} + F_{\Bl} \exp(i\,k_\B L) \\


          F_{1\r} &= -\nIIom \, F_{2\r} + \nIIom \, F_{2\l} \exp (i\,k_2 L) - \nIIom \, F_{\Br} +
                            \nIIom \, F_{\Bl} \exp(i\,k_\B L)\\


          F_{3\r} &= F_{2\r} \exp (i\,k_2 L) + F_{2\l} + F_{\Br} \exp(i\,k_\B L) + F_{\Bl} \\

         -F_{3\l} &= \nIIom \, F_{2\r} \exp (i\,k_2 L) + \nIIom \, F_{2\l} -
                            \nIIom \, F_{\Br} \exp(i\,k_\B L) + \nIIom \, F_{\Bl}

        \end{aligned}

    \end{equation}

    }