Unlike optical filters, severe and tough performances are required for astronomical IR filters. Very wide blocking range, often from 0.4μm to 2.8μm (sometimes ~ 5.0μm) is necessary due to the sensitivity of HgCdTe image sensor.
Vacuum and cryogenic environment also requires IR filters to be made of monolithic substrate to avoid the abrasion of cement caused by thermal shock. Eventually many and thick layers of dielectric films are necessary to be coated on both surfaces of substrate.
We provided two kinds of 120mm K-band filters, K-blue and K-red to FLAMINGOS-2 at Gemini. We fulfilled high transmission in passband by our proprietary magnetron sputtering technology.
As long as we know, 170mm MOSFIRE filter is currently the largest.
Maximum 200mm astronomical IR filters are now available.
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.