Infrared blocking materials

Abstract

Many modern optical imaging and detection systems operate not only in the visible, but in the infrared (IR), radio wave, and mm (sub-THz) spectral ranges. The rapid development of such systems requires the development of means of masking (suppression) of signals, for example, in the infrared region of the spectrum. Infrared blocking filters are also crucial for controlling the radiation load on cryogenic systems and optimizing the sensitivity of bolometric detectors in the far infrared region of the spectrum. In this case, the filters should minimize the radiation load on the cryogenic system, have a high thermal conductivity for heat sinks, avoid the reradiation, and be transparent in the THz spectrum. In this work, a comparative analysis of the distribution of thermal fields of two types of masking coatings-special paint and composite structure based on aluminum nitride-is carried out. It is shown that the latter can be more efficient IR filter elements due to the AlN charac teristic band of residual rays (Reststrahlen band, almost 100 % reflection) in the spectral range of 5-25 µm, where the main part of the radiation power of a black body at 300K is concentrated. "Cover-blocking IR" paints. It is well known that any paint in IR spectral range has emissivity from ε ≈ 0.84 (plastic, white) to ε ≈ 0.94-0.97 (oil, various colors) [1]. Still, from time to time there are advanced offers proposing different kinds of paints that presumably can diminish an object visibility in the IR. Here a comparison of one of such paints with ordinary gray oil paint in the visible and IR spectral ranges was made. In visible, really, such experimental paint that covers a part of metallic sheet can reduce the visibility of object (see Fig. 1) but in the IR,