An immersion lithography system is provided which includes an optical source operable to produce light having a nominal wavelength and an optical imaging system. The optical imaging system has an optical element in an optical path from the optical source to an article to be patterned thereby. The optical element has a face which is adapted to contact a liquid occupying a space between the face and the article. The optical element includes a material which is degradable by the liquid and a protective coating which covers the degradable material at the face for protecting the face from the liquid, the protective coating being transparent to the light, stable when exposed to the light and stable when exposed to the liquid.