Disordered solids such as ice i and vitreous silica have absorptivities that fall steeply with decreasing frequency in the far infrared, where the acoustic waves absorb radiant energy. These solids can be used as convenient far-infrared filters below 50 cm−1 and appear to be superior to the crossed transmission gratings and the wire reflection meshes commonly used.
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Wong et al. (1972) studied this question.
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