Investigation of the spectral dependence of the reflection coefficient of the factory-assembled aluminum mirror for the Shimadzu UV-2700 spectrophotometer

In this paper, we present the results of experimental investigation of the spectral dependence of the aluminum mirror reflection coefficient in the operating range of 185…900 nm. The aluminum mirror is a part of the Specular Reflectance Measurement Attachment to the Shimadzu UV-2700 spectrophotometer. We used experimental data obtained on the same spectro-photometer for a standard incidence angle of 5° for the reflection coefficient of a fused silicon dioxide plate as a reference sample. This is because the spectral characteristics of the optical parameters of fused silicon dioxide determined by the Sellmeier formular are well known. We used a standard quartz glass plate with a thickness of 2,2 mm and a spectrophotometer slit of 5 nm in our experiment. In this case it is possible to neglect interference effects due to multiple reflection. We found from our experimental data the spectrum of the absorption coefficient required for determining the calculated spectral dependence of its reflection coefficient in the spectrophotometer operating range. On the basis of this absorption spectrum the absolute values of the reflection coefficient of the quartz plate were calculated. This calculation was made for the normal incidence approximation and taking into account multiple reflections and dispersion of the refractive coefficient of fused quartz in accordance with the Sellmeier formula. The comparison of the spectra of calculated absolute and relative values of the reflection coefficient of the quartz plate measured on a spectrophotometer with experimental data for the reflectance of aluminum mirror made it possible to obtain the spectral dependence for the aluminum mirror for the entire operating range from 185 to 900 nm. It was found that spectral dependence of the reflection coefficient of a complete aluminum mirror was nonmonotonic. In case under consideration the deviations of its reflection coefficient from an ideal unit value do not exceed 10 % only in the spectral range from 350 to 670 nm. Thus, it is necessary to take into account the obtained spectral dependence of the reflection coefficient of the complete aluminum mirror for quantitative measurements in the entire operative range of the Shimadzu UV-2700 spectrophotometer from 185 to 900 nm.