X-ray mirrors and multilayers are used to reflect, focus, or monochromatize x-ray beams. Substrate materials are typically silicon, fused silica, Zerodur, ULE, or metals such as molybdenum, copper, or stainless steel. Substrates are polished to a few angstroms rms roughness and often coated with one or more layers to provide the desired spectral reflectivity.
Coatings can be damaged as a result of mishandling, contamination and/or chemical reaction, prolonged exposure to x-rays, exposure to poor vacuum, aging, or peeling due to poor coating adhesion and/or high stress. Incomplete or out-of-spec coatings may render an optic unacceptable. In all these cases, it is highly desirable to be able to
completely strip off a coating and recoat the substrate without the need for repolishing it. This is particularly important for optical substrates that are expensive or have a long fabrication lead-time.
This paper describes one such scheme. It involves pre-coating of mirror reflecting surfaces with a thin layer of chromium. Subsequent coatings can be stripped by etching away the chromium underlayer without damaging the substrate. Experimental results show that surface roughness is unaffected by the etching process in silicon and
zerodur, the two substrate material tested so far. The process is expected to be equally applicable to other glasses and can be extended to other substrate materials using appropriate underlayer / etchant combinations.