Reflectivity of the Primary Mirror

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 two such samples coated in August 1999 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.

Current Reflectivity and Scattering of Primary Mirror

The re-aluminization of the 8.3 meter primary mirror was conducted in August, 2003. This was the fourth re-coating after the arrival of the mirror at the summit of Mauna Kea in 1998. The reflectivity and scattering archived data of the primary mirror were measured by using 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).