INSITU OPTICAL-ELEMENT CLEANING WITH PHOTON ACTIVATED OXYGEN

The severe flux losses seen in synchrotron radiation beamlines due to carbon contamination of optical surfaces has stimulated a search for decontamination techniques to restore these surfaces to their pristine efficiencies. In situ techniques are preferred for their potential for minimizing labor and beamline downtime costs. Glow discharge activated O2, with or without additions of H2O, has been the most successful procedure to date and is capable of cleaning the surfaces without degrading their optical properties provided the system is properly designed and operated. The method is scarcely ideal, however, since real possibilities for contamination from the discharges exist, considerable instrument modification may be required to allow plasma access to the optics, and total cycle times are 1-3 days, which may be a significant operating cost on new, ultrahigh intensity beamlines. In this work we demonstrate the existence of a new in situ decontamination technique, presenting initial work showing that synchrotron radiation itself can sufficiently activate dry oxygen to successfully remove carbon contamination films. This technique offers particular promise in two areas. First, used in situ, the cleaning action takes place in exactly the same places where contamination occurs, since both processes are activated by the same radiation, and no instrument modifications are required. Second, it suggests that if the optical elements were continuously exposed to oxygen at an appropriate partial pressure, carbon contamination could be suppressed completely. We are now planning experiments to understand the physics, chemistry and kinetics of this new decontamination technique.