How organic impurities in the air affects laser? We have a Nd YAG laser pumped Optical Parameter Oscillator in our lab. A technician came to our lab (my professor called him for its maintenance) and while he was working on it, he told me that because of the organic impurities in the air, the crystals got contaminated. He showed me a layer formation on the crystal where the laser hits. He explained this is due to the organics in the air which interacts with laser and get deposited. I am not clear what kind of organics (aromatic or some other?) which creates this and how it is get deposited there? Can anyone please explain me in detail how the atmospheric impurities (especially organics) can cause damage on lasers?
 A: It would appear that your laser cavity is not sealed.  As a result, organics, and in general, dust particles, can float into the path of the laser light. some of those particles are heated as a result of absorption; some of those are close enough to one of the crystal faces (or mirror faces as well) and adhere to the face.  They then cause problems :-( .
What steps to take?  If possible, make the lab clean (HEPA filters, etc.), which may help the rest of your equipment from contamination as well.  See if there are seals on the laser itself which require replacement.  Consider putting the laser head inside a sealed box which you can back-fill with dry nitrogen (you'll need a good piece of glass with AR coating for the exit window, of course).
A: Deposition on mirrors and lenses is a problem because it reduces the precision and 
uniformity of the laser beam. With a powerful laser (especially those used for laser cutting) even a small deposit increases energy absorption which in turn can lead to a chain reaction that destroys the mirror or worse.
As for 'organics' I'm guessing that he means skin flakes and other sources of dust. 
