Collimator lens

[fab3]

Does anyone have any experience with these lenses? I have one on my old mazak and am wondering if they ever become stressed or dirty enough that it would effect cutting

 

[Foostrap]

Any lens could get stressed over time or due to cooling issues. This could then affect your mode quality, which will affect your cut quality. Easiest way to check for stress in lenses is to use polarizing filters. Actually Krugtech tip on using a LCD screen as backlight, and only one polarizing filter works really well. If you have a constant uniform color, the lens is good. If you see discolorations, spots, cross-type shade through the polarizing filter, the lens is stressed.

 

[fab3]

Footstrap
I regularly use polarizing filters on my focusing lens. I rarely see the tell tale "X" in the center of my lenses but often see little X's around the circumference. Does this classify as stress or is it just from the rings in my lens assembly? Also, I am still unclear what "mode" means as far as the laser? Beam roundness? Overall quality?

 

[Foostrap]

Those little x on the outside diameter could indeed be from the ring holding the lens being too tight.
The mode is refered as the shape of the beam coming out of the resonator. It should be round, have the same angle all around and be fairly flat at the bottom (although this depends on the resonator manufacturer). But most importantly, the diameter and depth of the mode should not change too much between a cold and a hot mode. If the hot mode is getting a lot narrower and deeper, you have a stressed output coupler. I assume the same would happen with a stressed collimator.

 

[nidbe]

hello, I work on a machine amada and I almost the same problem but how the polarization filters!?

 

[IRstuff]

The x's are probably from the mounting, but unless they're huge, there shouldn't be enough stress to affect performance.

"dirty" is a distinct possibility. There's just a lot of "stuff" in the air, such as pollution, soot, outgasses, that could deposit on lenses. They could degrade the transmission, as well as the apparent collimation itself, since they would tend to diffuse the laser energy. A more serious issue would be if the deposits are heavy enough to cause heating of the lenses. Non-uniform heating may cause thermal stresses that would affect collimator, but also may cause permanent damage to the lenses.

TTFN
faq731-376

 

[Foostrap]

You can either use 2 polarizing filters (same type you would use for a camera). Put one filter behind the lens, and one in front of the lens. Look into a light and rotate the front filter until no light goes through; then rotate slowly the other way until some light goes through. If the lens is stressed, you'll have discoloration (see attached picture from the II-VI lens analyzer).
Or you can use a LCD screen; open a empty document or anything that would bring up a white page, or something white. Put the lens in front of the screen. Then take a polarizing filter and rotate it until no light goes through, then rotate the other way and inspect.