Mirror coating 2003 in Subaru Telescope

The SUBARU Telescopehas four focal positions to allow different types of astronomical instrument. At present, there are four different Top Units; three types of secondary mirrorsand one primary focus unit. IR secondary mirrorwhich is one of the three units, has silver coated surface. Other secondary mirrorsare coated by aluminum for observations at visible wavelength. The silver coating for IR secondary mirrorwas first carried out in 1999 at the medium size (1.6 m) vacuum evaporationchamber in Mitaka campus of NAOJ at Tokyo JAPAN. Since then the reflectivity had deteriorated over the years. Then, we made a plan to recoatIR secondary mirrorin 2003 using the SUBARU’s large-size vacuum evaporationchamber at the summitfacility on Mauna Kea, Hawaii. Some tests were performed for silver vacuum evaporationat the base facility, and then the IR secondary mirrorwas recoatedat the summit. The reflectivity achieves 97.6% and 99.3% at the wavelength of 500 nm and 2000 nm, respectively. Degradation of the coat has not been seen 8 months after recoating. We also performed the recoatingof the aluminum surface of the primary mirrorin 2003. This year we made effort to simplify the procedure. The reflectivity is 91.2% and 97.4% at the wavelength of 500 nm and 2000 nm, respectively.