  A laser ablation system has been constructed and used to determine the damage
threshold of stainless steel, rhodium and single-, poly- and nanocrystalline
molybdenum in vacuum, at a number of wavelengths between 220 and 1064 nm using
5 ns pulses. All materials show an increase of the damage threshold with
decreasing wavelength below 400 nm. Tests in a nitrogen atmosphere showed a
decrease of the damage threshold by a factor of two to three. Cleaning tests
have been performed in vacuum on stainless steel samples after applying mixed
Al/W/C/D coatings using magnetron sputtering. In situ XPS analysis during the
cleaning process as well ex situ reflectivity measurements demonstrate near
complete removal of the coating and a substantial recovery of the reflectivity.
The first results also show that the reflectivity obtained through cleaning at
532 nm may be further increased by additional exposure to UV light, in this
case 230 nm, an effect which is attributed to the removal of tungsten dust from
the surface.
