Some of the most important components of a laser cutter are the optical elements.

1. Contaminated Optics within a Laser Cutter
Some of the most important components of a laser cutter are the
optical elements. These are components that either deflect the
beam (mirror) or allow the beam to pass through (lens).
Even when completely new, all optical components will cause some
degree of attenuation: in other words, remove a small amount of
laser power. Therefore, especially when the design of a laser
cutter incorporates a large number of optical elements the laser
power that arrives at the lens is less than the power that emits
from the laser source.
Contamination of the optical elements of a laser cutting
machine causes further attenuation and if left unchecked can have
a massive detrimental effect on cutting speeds and in turn
production efficiency.
Attenuation is more of an issue where the laser cutting
machine incorporates a laser source of a lower power.
For example, if a laser cutter outputting 30w incorporates four
mirrors, a combining optic for a positional diode and finally the lens,
then if each element draws 2 watts of power the net attenuation is
a 27% (almost 1/3rd) power loss.
Contaminated optics can often draw much more than 2w of laser
power so it’s quite possible that a laser cutting machine <50w can
be losing more than half its potential power simply through optical
attenuation and/or contamination.
Laser optics will suffer accelerated contamination if the main
application creates a high amount of debris; for example, laser
cutting wood or laser cutting card. An ineffective or incorrectly
specified exhaust system will further compound this problem

2. Low levels of contamination of laser optical elements can be easily
cleaned, however, if the contamination is allowed to build-up too
much it is often impossible to remove. At some point an
over-contaminated optic will draw so much power that the heat
generated will cause it to fail catastrophically.
For these reasons optical elements within a laser cutting
machine are deemed consumable items so for users where
the laser cutter is of strategic importance it’s a wise precaution
for the user to hold stock of replacement optics.
Over-cleaning of optical elements can cause undesirable removal
of the coatings, which is almost as bad as not cleaning them
enough. As a general rule of thumb it is the frequency of checking
for contamination that is more important and optics should only be
cleaned if they show obvious signs of contamination.
With most system designs, optics that are closer to the focal point
will contaminate faster than those that are closer to the laser
source so, for example, inspection of the lens should be performed
far more frequently than the first mirror.
We cover the cleaning of laser optics in another article.
At Lotus Laser Systems we manufacture a wide range laser,
marking and engraving solutions and we pride ourselves on the
quality and depth of knowledge of our support staff. Our experts
would be happy to advise you on this or any other aspect of your
laser system maintenance.
Source:- http://lotuslaser.blogspot.com/2016/03/contaminated-op
tics-within-laser-cutter.html