Oil-contamination problem in large-scale pulse-compressor

A heavy oil-contamination was observed on the optical components in LFEX pulse compressor. This contamination came from the wall of compression chamber, and the damage threshold of the mirror dropped to 1/2 or1/3 of the original value. The same contamination was observed in different compression chambers in our institute. The contamination materials were identified as Paraffin-oil and DBP (Di-n-butyl phthalate). Several cleaning schemes were tried, but no significant improvement was obtained. Finally, we found well-baked silica gel placed in the vacuum chamber improved the contamination very much. In a small vacuum chamber, the damage threshold increase by 3 times, and this result indicated the contamination of damage test sample. We also tried to remove contamination with dipping optics in the water-alcohol mixture, and we obtained almost the same improvements with the silica gel.