UBVRcIc filters:

Though UBVRI photometric system is rather classical in modern astronomy, UBVRcIc filters are still fundamental and important for telescopes.

Asahi provides UBVRcIc filters made by specified colored glass combination under the suggestion of Prof. Mike Bessell, RSAA.

We will also improve the transmission of conventional UBVRcIc filters by using interference films with the similar slopes in the future.

Notice: We currently produce B filter by L-38 (HOYA) and BG25 (Schott) instead of GG385 and BG12 (both Schott) because they are no longer available.

Narrow bandpass filters:

Narrow bandpass filters for H-alpha, SII or OIII emission line have been fundamental and important for astronomical sciences.

Narrow bandpass filters to target a redshift survey for H-alpha emitting galaxies are getting necessary for science groups.

More rectangular passband, precise center wavelength and FWHM, high transmission of filter are essential for H-alpha galaxy survey.

Asahi provided large format 250mm x 165mm redshifted H-alpha filters with good uniformity and monolithic substrate to Palomar Transient Factory.

We are currently interested in having the opportunity to produce large narrow bandpass filters for DECam or ODI in the future.

Large filters for next-generation wide field camera:

Next-generation wide field camera such as Dark Energy Camera (DECam) , Hyper Suprime-Cam (HSC), One Degree Imager (ODI), LSST,

Pan-STARRS or Discovery Channel Telescope (DCT) now comes of age.

Large filters that can satisfy these cameras should have excellent coating uniformity over the clear aperture and also high transmission in

passbａnd to shorten the exposure time as much as possible.

Asahi produced the largest ever 620mm DES g, r, i, z, y filters for Dark Energy Survey, and 600mm HSC g', z', Y filters for Subaru Telescope

by our proprietary large magnetron sputtering coater in 2011-2012.

Furthermore, we succeeded in coating the largest and hardest 620mm DECam u filter that had high transmission at any locations in spite of

UV wavelength in 2012.

New DECam VR filter with broad passbａnd was successfully coated by Asahi in 2014.

It was already delivered to CTIO and installed in DECam, Blanco Telescope.

Asahi past experiences to provide large filters:
▪ DES 620mm diameter g, r, i, z, y filters (2011-2012)
▪ DECam 620mm diameter u filter (2012)
▪ DECam 620mm diameter VR filter (2014)
▪ HSC 600mm diameter g', z', Y filters (2012)
▪ MegaCam 350mm x 300mm u filter (2014)
▪ OGLE 310mm x 310mm V, R filters (2009)
▪ KMTNet 310mm x 310mm B, V, Rc, Ic, g', r', i', z' filters (2012)
▪ Megacam 300mm x 300mm g + r filter (2013)
▪ Megacam 300mm x 300mm mosaic narrow bandpass filter (2009)
▪ Binospec 292.1mm x 209.55mm g, r, i, z filters (2013)
▪ Binospec 292.1mm x 209.55mm long pass filter (2014)
▪ PAU 208.8mm x 203.4mm u, g, r, i, z, y filters (2013)
▪ SALT HRS 350mm x 40mm dichroic mirror (2010)
▪ PTF 250mm x 165mm SDSS g', narrow bandpass filters (2011)
▪ Suprime-Cam 205mm x 170mm B, V, R, I, u', g', r', i', z' and many narrow bandpass filters (1997-2012)

Broadbａnd AR coating:

AR coating is quite basic and essential technology for any astronomical instruments, because the performance determines the available

wavelength in cameras or spectrographs.

The AR film that can cover the unprecedented broadbａnd is currently getting important to build the next-generation spectrograph.

Broadbａnd AR coating also contributes to reduce the ghost caused by multiple reflection on dichroic beam splitter.

Asahi succeeded in developing the incredible broadbａnd AR coating which covers from 380nm to 1800nm.

SDSS u, g, r, i, z-bａnd filters:

Sloan Digital Sky Survey (SDSS) is currently the most common and important photometric system in astronomy. The large volume of survey

data gotten by the SDSS team became the cultural legacy. Broad bandpass filters in the wide field camera are basically defined as Sloan filters.

Asahi provided the world's first SDSS (Sloan) u, g, r, i, z-bａnd filters to Apache Points Observatory (APO) twenty years ago.

Unlike the similar SDSS (Sloan) filters sold by internet, we produce on the basis of the spectral response of filters at APO 2.5m telescope under

the instruction of SDSS astronomer.

Notice: Due to the quality issues of Schott colored glass, we currently use an alternative glass or interference film instead of the original filter recipes.

Mauna Kea Observatories Y, J, H, Ks filters:

Unlike optical filters in astronomy, there are much harder requirements for astronomical IR filters.

HdCdTe imaging sensor requires IR filters to have very broad blocking range from 0.4μm to 2.7μm, sometimes beyond 3μm.

Also vacuum and cryogenic environment requires to be made by monolithic substrate.

Eventually huge layers of thick interference films are necessary to achieve both requirements.

Mauna Kea Observatories (MKO) Y, J, H and Ks filter specifications were defined by Dr. Alan Tokunaga, University of Hawaii.

MKO filters are currently standard photometric system in NIR region as SDSS u, g, r, i and z-bａnd filters in optical region.

We produce Y, J, H, Ks filters by magnetron sputtering and ion assisted deposition technology with single substrate on the basis of MKO

filter specifications, and measure the transmission curve under 77K cryogenic condition by ourselves.

Dichroic mirror:

Dichroic mirror (beam splitter) is getting more important to build next-generation spectrographs or multiple color cameras for GRB observation.

Dichroic mirror gives the influence siginificantly to the total performance of two or more spectrographs or cameras in terms of imaging quality

ａnd available wavelength range.

▪ High reflection in broad band
▪ High transmission in broad band
▪ Sharp transition from reflection to transmission (As small as polarization separation)
▪ As small as reflected wavefront error after the coating
▪ As small as transmitted wavefront error after the coating

Only few vendors can achieve all requirements as above simultaneously in the world.

Asahi is one of such vendors to supply the true dichroic mirror to astronomers.

Asahi is currently developing the unprecedented large 400mm x 350mm dichroic mirrors that require such performances for Prime Focus

Spectrograph at Subaru Telescope.