Reflectivity of the Subaru Telescope's Mirrors

Telescope Efficiency

The following figure shows the total efficiency of the Subaru Telescope's mirror system on each focus at February 2019. The reflectivity data had been taken from January 30 to February 8, 2019.

Reflectivity of the Primary Mirror (M1)

The Subaru Telescope primary mirror was recoated with Aluminum on October 20, 2017. This was the eighth coating work from its arrival at Maunakea, Hawaii in 1998, and was about four years from the previous recoating on August 15, 2013. After the recoating, we measured the reflectivity outside of the vacuum chamber using a portable measuring instrument named "Subaru Portable Spectrophotomer (SPS)" on October 23, 2017. The reflectivity of the primary mirror has been measured in-situ on the telescope since October 10, 2017, by using SPS. The following figure shows the time variation of the reflectivity the primary mirror.

Plain text data are available as below.

A number of microscope slide glasses were placed in the vacuum chamber and coated with Aluminum together with the primary mirror to make "witness samples." The reflectivity of a witness sample was measured with a Hitachi U-4001 spectrophotometer at the Base Facility in Hilo on December 26, 2017. The following figurere shows the reflectivity of the witness sample.


Reflectivity of the Infrared Secondary Mirror (IR-M2)

The Subaru Telescope infrared secondary mirror (IR-M2) was recoated with Silver at the Subaru Telescope summit faciliy on August 22, 2008. This was the third coating work, and was about five years from the previous recoating on April 2, 2003. The refectivity of IR-M2 immidiately after mirror recoating in 2008 was measured with the witness sample technique by a Hitach U-4001 spectrophotometer at the Base Facility in Hilo on August 25, 2008. We have measured the IR-M2 reflectivity with SPS-XWW and IR-M2 Jig since November 5, 2018.

Plain text data is also available as below.


Reflectivity of the Cassegrain Optical Secondary Mirror (CsOpt-M2)

The Subaru Telescope Cassegrain optical secondary mirror (CsOpt-M2) was coated with Aluminum at the Pilkington Technical Mirror Corp on December 17, 1998. The following figure shows the reflectivity of the Cassegrain optical secondary mirror. The refectivity of CsOpt-M2 immidiately after mirror coating is not available. As a reference, we also plot an Aluminum reflectivity coated in hight vacuum measured in air, which is tabulated in "The Optical Properties of Metallic Aluminum", D. Y. Smith, E. Shiles, and Mitio Inokuti, in "Handbook of Optical Constants of Solids", Vol. 1, p. 369-406 (1997).

Plain text data is also available as below.


Reflectivity of the Nasmyth Optical Secondary Mirror (NsOpt-M2)

The Subaru Telescope Nasmyth optical secondary mirror (NsOpt-M2) was coated with Aluminum at NAOJ Mitaka campus on August 26, 1999. The following figure shows the reflectivity of the Nasmyth optical secondary mirror. The refectivity of NsOpt-M2 immidiately after mirror coating is not available. As a reference, we also plot an Aluminum reflectivity coated in hight vacuum measured in air, which is tabulated in "The Optical Properties of Metallic Aluminum", D. Y. Smith, E. Shiles, and Mitio Inokuti, in "Handbook of Optical Constants of Solids", Vol. 1, p. 369-406 (1997).

Plain text data is also available as below.


Reflectivity of the Infrared Tertiary Mirror (IR-M3)

The Subaru Telescope infrared tertiary mirror (IR-M3) was recoated with Silver on December 17, 2014. This was the fourth coating work, and was about five years from the previous recoating on January 26, 2009. The refectivity of IR-M3 immidiately after mirror recoating in 2014 was measured with a witness sample technique by a Hitach U-4001 spectrophotometer at the Base Facility in Hilo on January 22, 2015. IR-M3 reflectivity has been measured with SPS-XWW since September 7, 2018.

Plain text data is also available as below.


Reflectivity of the Optical Tertiary Mirror (Opt-M3)

The Subaru Telescope optical tertiary mirror (Opt-M3) was recoated with Aluminum on December 3, 2014. This was the third coating work, and was about nine years from the previous recoating on October 5, 2005. The refectivity of Opt-M3 immidiately after mirror recoating in 2014 was measured with a witness sample technique by a Hitach U-4001 spectrophotometer at the Base Facility in Hilo on January 21, 2015. Opt-M3 reflectivity was measured on February 7, 2019, with SPS-XWW.

Plain text data is also available as below.


Subaru Portable Spectrophotometer (SPS)

Subaru Portable Spectrophotometer (SPS) is a compact, portable, and powerful reflectivity measuring instrument developed by Subaru Telescope in 2017. SPS can measure the absolute spectral reflectivity of the primary mirror in-situ on the telescope. Its small dimension (450 mm x 310 mm x 370 mm) and light weight (5.9 kg) enable in-situ measurement on the primary mirror. SPS covers the spectral range from 380 nm to 1000 nm with 2 nm resolution. The incident angle to the measuring surface is 12 degrees. The measurement beam size is about 12 mm in diameter. The statistic error is less than 0.2% in rms between 450 nm and 900 nm, and there are less than 0.6% in rms at 380-450 nm and 900-1000 nm ranges. The systematic error is expected to be less than 0.2%.

We wish you will make a same type of measuring instrument and measure the absolute spectral reflectivity of telescopes at your observatory. For your convenience, we will open detailed information of SPS.

SPS-XWW

We have upgraded SPS with eXtra Wide Wavelength (XWW) capability since August, 2018. Now the reflectivity at near infrared between 950 nm and 1650 nm with 10 nm resolution can be measured simultaneously with the original range between 380 nm and 1000 nm.

IR-M2 Jig

To measure the Subaru Telescope infrared secondary mirror (IR-M2), a special jig was designed. By using this jig, we can measure the reflectivity easily, securely, and safely.

CsOpt-M2 and NsOpt-M2 Jig

To measure the Subaru Telescope Cassegrain optical secondary mirror (CsOpt-M2) and the Nasmyth optical secondary mirror (NsOpt-M2), a special jig was also designed.

Opt-M3 and IR-M3 Jig

A special jig to measure the Subaru Telescope optical tertiary mirror (Opt-M3) and the infrared tertiary mirror (IR-M3) was designed and is now under testing.

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Old Information

The followings are old, however these are still valuable. For your information, we continue to show the old information below.

Reflectivity of the Primary Mirror

The re-aluminization of the 8.3 meter primary mirror was conducted in August, 2010. This was the sixth re-coating after the arrival of the mirror at the summit of Mauna Kea in 1998.

A number of microscope slides are placed in the coating chamber when the primary mirror is aluminized. These slides are then brought down to the Base Facility in Hilo, where their reflectivity is measured in the laboratory by a spectrophotometer.

The reflectivity of such samples coated in August 2010 is indicated in the following figure. They should be indicative of the reflectivity of the primary mirror. Degradation of the primary mirror's performance is kept to a minimum by regular CO2 snow cleaning.

Plain text data is also available as M1-2010s.txt.

Current Reflectivity and Scattering of Primary Mirror

The reflectivity and scattering archived data of the primary mirror is monitored with micro-Scan (TMA Technologies, Inc.). The reflectivity and scattering are fairly stable at about 82 % and 80-100 A, respectively, after 400 days from re-coating.

Reflectivity of IR Secondary Mirror

Infrared (IR) secondary mirror was re-coated with only silver in April, 2003. Reflectivity of silver coated the infrared secondary mirror at the wavelength from 300 to 2,500 nm (Kurakami et al. 2004).


Further information

This page was last updated on March 11, 2019. Questions regarding this page should be directed to Hirofumi Okita ( ).


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