Comparisons of reflectance spectra. (a) Comparison of a reflectance spectrum obtained using a narrow-band detector (N-MCT) with that using a mid-band detector (MCT). Sample contains 3.4 wt.% water. Both spectra were obtained with an aperture of 30 μm × 30 μm and 1,024 scans in air. A gold mirror was used as a reflectance reference. The reflectance signal from the gold mirror was saturated at wavenumbers below 6,000 cm−1 when the N-MCT detector was used. Therefore, reflectance of the glass sample was higher than that expected from the refractive index of the glass sample. (b) Comparison of a reflectance spectrum obtained at 100 Pa with that obtained in air. Both spectra were obtained with an aperture of 50 μm × 50 μm and 2,048 scans against a gold mirror using an MCT detector.