  We have measured the optical reflectivity $R(\omega)$ of
$Eu_{0.6}Ca_{0.4}B_{6}$ as a function of temperature between 1.5 and 300 $K$
and in external magnetic fields up to 7 $T$. The slope at the onset of the
plasma edge feature in $R(\omega)$ increases with decreasing temperature and
increasing field but the plasma edge itself does not exhibit the remarkable
blue shift that is observed in the binary compound $EuB_{6}$. The analysis of
the magnetic field dependence of the low temperature optical conductivity
spectrum confirms the previously observed exponential decrease of the
electrical resistivity upon increasing, field-induced bulk magnetization at
constant temperature. In addition, the individual exponential magnetization
dependences of the plasma frequency and scattering rate are extracted from the
optical data.
