Resuscitation of carbon-contaminated mirrors and gratings by oxygen-discharge cleaning. 2: Efficiency recovery in the 100-1000-eV range.

The capability of dc oxygen-discharge cleaning to resuscitate the efficiencies of mirrors and gratings contaminated by synchrotron radiation has been studied over the 100-1000-eV photon-energy range. The contamination- induced efficiency degradation was severe at the carbon K edge, even for a low contamination level. A large reduction in the mirror reflectance was also observed just below the carbon K edge and at high energies, which was shown by a model calculation to be ascribable to an interference effect in the carbon film. Cleaning resulted in a dramatic recovery of the efficiencies; their increase amounted to more than 1 order of magnitude at these energies. The removal of contaminant deposits also led to a reduced scattering level and a restoration of the grating-blaze effect; these contribute to an improvement in the monochromator performance, both regarding the stray-light level and the diffracted-light intensity.