Outgassing rates and optical absorption coefficients of five kinds of black colored coatings, i.e. Ultra-Black NiP (UB-NiP), Phos-black II, Raydent, diamond-like-carbon formed on electrochemical buffed SS surface (ECB+DLC) and Alumite, have been examined to be used as an optical absorber in the high vacuum system of interferometric gravitational wave detectors. The outgassing rate and optical absorption coefficient of UB-NiP were q = 2.2×10-5 t -1.2 [Pa m3/sec/m2] (0.2≤t [hour]≤100) and 99.89% for 1064 nm in wavelength, respectively. These are considered as high performances. ECB+DLC had the optical absorption coefficient of 65% and its outgassing rate was two orders of magnitude lower than that of UB-NiP. It is concluded that UB-NiP is suitable for coating on small optical devices such that high efficiency of optical absorption was required. On the contrary, ECB+DLC coating is useful when it is applied to devices having a large area.
