I understand that the compressed air for the laser optics purge (first step of cleaning) such as mirrors or lenses should be "clean", but does anybody can explain me what really does it mean "clean" and how can I verify/qualify it ?
Thank you in advance ;)
The compressed air must be free of moisture and oil. The oil itself comes from lubrication of the compresssor and the moisture is from the air that is being compressed. A water trap, followed by a filter to trap oil residues will help. That way the compressed air now free of oil droplets or water droplets can be used to clean optics and blow dust off the optical system and table.
Compressed air must be oil, moisture and dust free. One can use manual air blower instead of using compressed air if it is not filtered properly for oil, moisture and dust.
So in general, I can assume that coalescing compressed air filter should be enough, right?
Usually, when I need to clean an optical surface with compressed air of unknown quality, I use following test. I take a piece of initially clean first surface reflecting mirror or piece of clean silicon wafer and direct on it compressed air from the distance of a few millimeters and during a couple of minutes. So, distance should be shorter, and time have to be sufficiently bigger usual cleaning parameters. Than you should carefully examined scattering of the light from test mirror surface. If you see no scattering light difference along it, no traces of compressed air, you can use this compressed air with no risk to damage your working surface.
If possible, i use nitrogen gas free from oil and moisture. It should be very easy to access nitrogen gas in the laboratory. I did compare cleaning optical surfaces using the compressed air and nitrogen before. The outcomes are surprising if you look at the surfaces under microscope. I would strongly suggest to use nitrogen gas to clean optical surfaces.
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