I own a Cincinnati 4kw Laser. We clean the focal lens daily with some laser fabric that you can buy at lasermech and Acetone. Although, you can use cotton swabs and Acetone for a quick clean. What is this for?? If this is you're first time cleaning this lens it is most likely damaged. Also, please don't put the lens down on a hard surface like you have in the picture.
Thanks, it's not a hard surface it's a mouse pad and a special paper the fabricator gave us to clean the lenses. I cleaned it with alcohol and "that kind of" paper, and tried several things more but nothing seems to work. It tainted in an accident, a plastic holder melted and damage one yag rod and the smoke seems to get stuck into the lens tainting it.
I know that our focal lenses eventually go bad. We have a small tester to make sure we don't keep running on it. If it cracks, Toxic Zinc crap gets everywhere. Highly toxic to inhale. Although, I'm not exactly sure you have the same type of lens. I don't even know what machine you are running with, but yes, Anything that gets in a lens needs cleaned out immediately to prevent further damage. Our system generally warns us if there is possible smoke or debris that is getting on the lens. You will probably be looking to get a new one. Laser Mechanisms, Inc. - Laser Beam Delivery Components supplies a bunch of different types of lenses for lasers.