Reflection loss correction method for accurate absorbance spectrum analysis of coloured glasses

Four reflection loss correction methods have been investigated, theoretically and by analysing the measured absorbance spectra for eight samples prepared from the same Cu-doped soda–lime–silica glass. Method A, based on the measured refractive indices, was found to be the most practical and accurate. The methods B (subtracting the absorbance of an undoped host glass) and C (subtracting a thinner sample's absorbance spectrum of the same glass) rely on additional measurements of a reference sample. Method A (that only removes the reflection loss from the absorbance) would show most clearly any additional loss due to the sample quality: polished surfaces and inhomogeneities, scattering by the glass structure, or absorption due to the impurities and host glass. Methods B and C would provide errors with similar wavelength dependence as the remaining attenuation coefficient spectrum, which would be very difficult to notice. Method C provides for the best quality samples the same median spectrum as Method A, but shows larger uncertainties than Method A, because the corrected spectrum needs to be multiplied by the inverse thickness difference of the two samples. Method D (subtracting a constant reflection loss) would cause errors due to the wavelength dependence of the glass refractive index.