Coating the 2-m level primary mirror with protected aluminum

In order to evaporate the O 2.4m large-scale speculum, we have developed a high-vacuum resistance evaporation machine which is of the nation’s largest bell-type, and we first propose to use the structure of the protected-Al coating with SiO coating by evaporating from top to bottom. The results show that the non-uniformity of aluminum coating is no more than 5.17% within 1.8 meters in diameter, also after environmental testing, there is no change on the mirror surface, and the reflectance decreased less than 1%. The average of the speculum reflectivity is Rav<88%@350nm-1800nm and Rav<90%@ 400nm-2500nm.We have separately completed the O 1.8m plane mirror in April 2011 and the O 1.8m concave mirror in October 2011. The results show that the PV value is less than λ/10 after evaporation and the RMS value has no change.