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The optical performances of components exposed to high power laser beams during long periods are generally decreasing with time. We analyze surface modifications that occur after some hundreds of hours at a fluence of 0.5 kW/cm2 to 10 kW/cm2. The results obtained with two dedicated test benches over thousands of hours are discussed. Exposition of tens of components has been achieved in the multi-component bench to simulate real optical systems and to acquire statistical confidence in the results. The single component bench allows continuous measurements of the surface temperature and of the scattered light. These measurements show how these beamprints can lead to the surface destruction. We investigate the effects of the beam fluence, the laser wavelength and the chamber pressure. Experiments at two wavelengths have shown that the deposition rate and the surface absorption increase with decreasing wavelength. The efficiency of oxygen in reducing the contamination speed has been investigated using absorption mappings. Laser cleaned surface absorptions are comparable to initial measurements, showing that damage did not occur. ESCA analysis of the beamprints showed that a few nanometers carbon layer has been implanted.
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Laurent Bruel "Environmental effects on optical component aging", Proc. SPIE 4932, Laser-Induced Damage in Optical Materials: 2002 and 7th International Workshop on Laser Beam and Optics Characterization, (30 May 2003);

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