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发布于 2012-11-29 08:46

Astronomical filters

Asahi Spectra has supplied astronomical filters with science-grade to world famous observatories, institutes or universities for over 15 years. Unlike cheap astronomical filters for the amateurs, Asahi astronomical filters are definitely manufactured for professional astronomers to meet rigid specifications and environmental durability.
New discovery and progress of science shall be emerged by Asahi filters. Asahi astronomical filters are actually installed in telescopes in Hawaii, Chile, Canary, Arizona, South Africa, Australia or other important observatories.

Asahi astronomical filters have been supplied or   installed in the followings

DECam, Fermi National Accelerator Laboratory Las Cumbres Observatory Global Telescope Network
NASA Goddard Space Flight Center W. M. Keck Observatory
LBC, Large Binocular Telescope MMT Observatory
IMACS, Magellan Telescope Kitt Peak National Observatory
LFC, Hale Telescope National Optical Astronomy Observatory
SDSS, Apache Point Observatory Smithsonian Astrophysical Observatory
Pan-STARRS, UH 2.2-meter Telescope Carnegie Observatories
European Southern Observatory ULTRACAM, William Herschel Telescope
OGLE, Warsaw University Telescope Instituto de Astrofisica de Canarias
FORS1, Very Large Telecope  
Hyper Suprime-Cam / Suprime-Cam, Subaru Telescope  
South African Large Telescope  


Large Filters for next-generation wide field telescope

Dark Energy Survey (DECam), WIYN Observatory (ODI), Subaru Telescope (HSC), Pan-STARRS, Discovery Channel Telescope or LSST......
Next-generation wide field telescopes now come of age. High transmission large filters with good coating uniformity are definitely one of the essential components, and help the success of survey and the great discovery.


Asahi provided the largest ever 620mm DES g, r, i, z and y filters to CTIO, Chile not by conventional ion assisted deposition but the state-of-the-art magnetron sputtering technology.

Furthermore, we succeeded in developing the hardest ever large u filter. DECam 620mm u filter Asahi produced has the significantly high transmission at all positions on the clear aperture despite of the UV wavelength.


Astronomical dichroic mirror

                 SWIMS165mm x 125mm dichroic for Tokyo-Atacama Observatory

RWF :0.215 lambda (pv)
        140mm x 110mm ellipse
TWF :0.376 lambda (pv)
        140mm x 110mm ellipse
Lambda :632.8nm


Astronomical dichroic mirror plays an important role to observe the multiple colors simultaneously and effectively, especially in GRB observation.
Dichroic mirror determines the total optical performance of camera such as separation of each spectral band or imaging quality. That is, the dichroic is definitely one of the key components in your camera.
Therefore, unprecedented specifications are always required for astronomical dichroic mirror compared to other applications.
  • High reflection with wide range
  • High transmission with wide range
  • Sharp transition from reflection to transmission in spite of polarization
  • Both good reflected wavefront (RWF) and transmitted wavefront (TWF)
In addition, the beam on the dichroic becomes ellipsoidal shape due to the angle of incidence, so large clear aperture is often requested.

Asahi is currently developing the astronomical dichroic mirror which can meet the requirements as above simultaneously for optical wavelength as well as IR.


Astronomical IR filters


Unlike the filter for optical region, there are hard requirements for IR filter which is mounted in vacuum and cryogenic dewar. Both requirements, monolithic substrate and long blocking range for astronomical IR filter make the fabrication difficult.
These days, the required blocking range becomes longer even from optical wavelength to e.g. ~ 2.6um due to the spread of excellent HgCdTe imaging sensor. In addition, recently larger size is required like wide field CCD mosaic camera. We are currently developing IR filter which can meet monolithic substrate, long blocking range and larger size at the same time.


WFCAM Z, Y / The Mauna Kea near-infrared J, H, K filter   set

The Mauna Kea near-infrared J, H and K filters were defined by Dr. Alan Tokunaga, IfA, University of Hawaii and become the standard photometric system in NIR region like SDSS in the optical. WFCAM Z and Y filters are also standard for IR astronomers. Each passband is achieved by dielectric interference film coated by ion assisted deposition, so spectral response is stable under 77 K cryogenic and vacuum condition.


SDSS filters / u, g, r, i, z-band

Notice: Due to the serious quality problem in colored glass, it is probable to use alternative glass instead of the original filter prescription.


SDSS(Sloan Digital Sky Survey) photometric systems are currently the most common, important and unignorable in astronomy. We proudly supplied SDSS 2.5m telescope at Apache Point Observatory with original SDSS filters, where they have been used as the basis of SDSS photometric systems.
We know the specifications SDSS project defined, and strictly observe them. We promise that we will supply genuine SDSS filters which completely meet the original specifications for you.


Johnson / Bessell U, B, V, R, I filters



Notice: Due to the discontinuation of GG385 and BG12 (Schott), we currently make B filter by using L-38 (HOYA) and BG25.


Though more basic and rather classical photometric system, Johnson / Bessell filters are still important for astronomers.
We can supply not only typical Johnson / Bessell filters made by only colored glasses, but also the filters with interference film combination.


Narrow bandpass filters

H-alpha, H-beta, OIII, SII or Stroemgren u, v, b, y...
omical narrow bandpass filters are necessary for most of telescopes and play the important role of the scientific advances.
Generally it is harder to fabricate the narrow bandpass filter, because the minimal error for film design is required to form the narrow passband, especially narrower e.g. 5nm FWHM.
Furthermore, smaller tolerance for CWL or FWHM is often required than broad bandpass.
It means it is the key technology to keep the good uniformity over the clear aperture when the large format narrow bandpass filter is requested


Super broadband AR


AR coating that can cover the unprecedented broadband are currently required to achieve the optical system for next-generation spectrograph.
Broadband AR coating can also contribute to reduce the ghost caused by multiple reflection in dichroic beam splitter.


We considered the performance of AR coating affected the total performance of instrument significantly.

Asahi succeeded in developing the incredible super broadband AR coating that covers from 380nm to 1800nm for the ambitious spectrograph.





北京晨辉日升光电技术公司 2012