Читать книгу Continuous Emission Monitoring - James A. Jahnke - Страница 138

An optical filter allows light only in a narrow spectral region to pass through it. Interference filters, constructed by vacuum deposition of metallic films on glass or other materials, are commonly used in the infrared region of the spectrum. Neutral‐density filters are used to attenuate light of all wavelengths equally, being made of quartz or glass with a thin metal coating having a specified optical density.