I'm measuring transmittance through and reflectance from thick glass samples, using spectrophotometers. Does anyone know if there's an exact solution for the surface transmittance r, surface reflectance t, and absorption coefficient A (as in Beer-Lamberts law). For a specific wavelength the equation for total reflected light from the sample, R, is R=r(1+t2e-2Ad)/(1-r2e-2Ad) and the equation for the total transmitted light through the sample, T, is T=t2e-Ad/(1-r2e-2Ad) R and T are measured, thus known variables. So we have the unknown material properties r, t, and A, and two equations. I can measure a sample of the same material with another thickness d and then I have four equations and three unknowns. This should theoretically be enough but the algebraic becomes very complicated and I wonder if there actually is an analytic solution. Of course I can approximate 1>>rre-2Ad in the second equation and obtain A by dividing the second equation for one thickness with the same equation for another thickness, but then it is no longer the exact solution. Any help is most appreciated, as always. Thanks!