Unmet Need
Millimeter-wave cryogenic receivers require rejection of infrared (IR) radiation to reduce thermal loads on the cold stages of the cryostat. As telescope apertures increase in diameter to accommodate larger focal planes, the requirements for infrared filtering become more stringent, while the fabrication of filters becomes correspondingly more difficult. This is a particular problem for current cosmic microwave background receivers, which have receiver apertures approaching 1 m in diameter. Absorptive filters have also been extensively used, in which a material with low loss at millimeter wavelengths but strong absorption in the IR absorbs power and conducts it to higher-temperature stages of a receiver. However, absorbing filters require anti-reflection coatings and lose effectiveness as their diameter increases, because the centers of the filters tend to heat and re-radiate further down the optical chain.
Technology Overview
The inventors have developed highly transparent, broadband, and tunable IR-blocking optical filters composed of small scattering particles embedded in an aerogel substrate that diffusely scatter infrared radiation. The aerogel is ultra-low-density (50-200mg/cc) with a low index of refraction, removing the need for anti-reflection coatings and allowing for ultra-broadband operation across frequencies ranging from zero to 10 THz. The size of the particles can be tuned to give variable cutoff frequencies.
Stage of Development
Test filters have been produced and tested.
