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.
Mauna Kea Observatories (MKO) filter specifications were defined by Dr. Alan Tokunaga at University of Hawaii.
MKO filters are currently standard photometric system in NIR region such as SDSS u, g, r, i, z-band filters in optical region.
We produce Y, J, H, Ks filters by our proprietary magnetron sputtering technology with monolithic substrate on the basis of the MKO filter specifications.
We also measure and evaluate the transmission under 77K cryogenic condition.