Cleaning Dielectric Mirrors
Dielectric mirrors can be cleaned with acetone and appropriate cleaning tissue, for example this one Whatman 105 Lens Cleaning Tissue if its just a bit dust you can lay the lens paper on the mirror, put 2-3 drops acetone on the lens paper and pull it away over the surface. It should be dry when the lens paper is completely pulled away.
If there is more dirt or fingerprints its the best to fold the paper several times and grip it on one edge where its folded with hemostats.
Add some acetone and wipe the mirror ONCE. If you need to wipe again you might fold it again and use a new edge or take a new paper.
- Fingerprints might attack the coating of dielectric mirrors if they stay on it for days/weeks so it might be the best to clean them right after accidently touching them.
- A word of warning here on dielectric mirrors. They typically use fluorides of light elements such as magnesium. These have very low but still significant water solubility, getting a film of water on them can be quite bad so that a say 135nm layer carefully coated to reflect say green could suddenly have patches only say 100nm or so because some of it has got washed away in water so it then it reflects blue instead of green. Evaporating acetone very fast in a cold damp room can produce significant water condensation. A warm hair drier should stop this from happening, I don't have a perfect answer, I am just pointing out something to be aware of. - Jeff