Unlike optical filters, severe specifications and performances are generally required
for astronomical IR filters. Very wide blocking range, often from 0.4μm to 2.8μm,
(sometimes ~ 5.6μm) is necessary, because HgCdTe detectors are sensitive across
a wide range of wavelengths.
Using environment in vacuum and cryogenic condition also requires IR filter to be
made of a monolithic substrate to avoid abrasion of epoxy glue by thermal shock.
Eventually many and thick layers of interference film are necessary to be coated on
both surfaces of substrate.
We provided the “Y+J filter” for the iLocater / Large Binocular Telescope in 2022.
Extremely high transmission in passband was achieved thanks to our proprietary
magnetron sputtering technology.
Recently, thermal blocking filter is often asked as well as Mauna Kea Observatories Y, J, H, Ks filters.
We provided the thermal blocking filters to Dunlap Institute for Astronomy and Astrophysics in Canada.
They were coated by the state-of-the-art magnetron sputtering technology on the monolithic fused silica substrate, and had
high transmission passband and excellent blocking performance in IR (i.e. thermal) wavelengths.
Actual transmission was also measured and evaluated in 77K cryogenic condition by using the witness sample at Asahi factory.
