A Wavelength Standard for the Near Infrared Based on the Reflectance Of Rare-Earth Oxides

This work describes the techniques used to prepare and analyze a reflectance wavelength standard composed of three rare-earth oxides. A mixture of dysprosium oxide (Dy₂O₃), erbium oxide (Er₂O₃), and holmium oxide (Ho₂O₃) provides a pressed powder specimen exhibiting a near infrared reflectance spectrum characterized by many discrete absorption minima in the wavelength range 700 to 2000 nm. The object of this activity was to develop a wavelength standard for improving the accuracy of reflectance measurements in the near infrared. The reflectance minima of the rare-earth oxide mixture was analyzed for the effects of varying spectral resolution and temperature. The uncertainties associated with the various parameters affecting the measurements and the determination of the location of the reflectance minima have been analyzed. The overall uncertainty in the location of these reflectance minima is believed not to exceed ± 1 nm.