  We compute the frequency and magnetic field dependencies of the reflectivity
$R(\omega)$ in layered superconductors with two alternating intrinsic Josephson
junctions with different critical current densities and quasiparticle
conductivities for the electric field polarized along the c-axis. The parameter
$\alpha$ describing the electronic compressibility of the layers and the charge
coupling of neighboring junctions was extracted for the
SmLa$_{1-x}$Sr$_{x}$CuO$_{4-\delta}$ superconductor from two independent
optical measurements, the fit of the loss function $L(\omega)$ at zero magnetic
field and the magnetic field dependence of the peak positions in $L(\omega)$.
  The experiments are consistent with a free electron value for $\alpha$ near
the Josephson plasma frequencies.
