  In this study we analyze the transmission spectrum of a thin plate of Cuprous
Oxide in the range of the absorption of the yellow exciton states with the
coherent transfer matrix method. We demonstrate that, in contrast to the usual
analysis using Beer's law, which turns out to be a rather good approximation
only in the spectral region of high principal quantum numbers, a consistent
quantitative description over the whole spectral range under consideration is
possible. This leads to new and more accurate parameters not only for the
Rydberg exciton states, but also for the strengths of indirect transitions.
Furthermore, the results have consequences on the determination of the density
of electron-hole pairs after optical excitation.
