Co2 laser tem mode analysis

while trying to align mirrors on the laser I noticed the burn pattern at the first mirror didn’t appear uniform to me, so I ran a bunch of test pulses from 10 through 15 % . It started firing at 13 .

Can anyone advise whether this burn pattern is normal or would you say there is an issue with this laser tube? This is a brand new laser machine I just purchased.

For reference it is a 150W YL-Laser

Chiller temp was 64F/18C , ambient temp was 69F/20.5C

Minimum firing at 13% for a 130W tube doesn’t seem too out of line but I haven’t worked directly with tubes of that size. As reference, I have an 80W tube that has a minimum firing power of 9%.

The burn pattern is not ideal but I would suggest testing at higher power. I don’t know if this was just a way of avoiding responsibility but I was told that there may be a minimum power value at which tem mode shifts to tem00. Again, as reference, my tube shifts to tem00 only at 22% power. I was told to test at 45% so take that for what it’s worth. I’d suggest at least trying higher values to see if that tem01 goes to tem00.

At what distances were these tests done?

The laser tube head is about 3/4 inch from the taped hole.

Thanks, I’ll try at higher values.

Does this mean I shouldn’t use the laser at values below a value that produces a TEM00 pattern?

I don’t think that’s necessarily the case. Only to know how the laser might behave under those circumstances.

So all these tests were before M3 or were these done after M3 but before lens?

Sorry if my terminology is mixed up but it’s my understanding that it goes - Laser Tube, M1, M2, M3, Lens. These tests were all done before the laser beam hits any mirror, so directly out of the laser tube, just in front of M1. The laser tube is about 3/4 inch from the hole in the mirror stand of M1.

Sorry. I misread. Thought you meant lens tube when you clearly said laser tube. It’s hard to say but some of these dots look fairly large coming straight out the tube.

I’m having a hard time finding any good specifications for your laser but your beam was listed at 2.5mm. I didn’t see anything about beam divergence values. Can you measure the widest dot in your samples and check how wide they are?

the bottom left dot, approximately the largest is ~ 3.7 x 5.2 mm . On average I’d say they’re all just over 4 mm.

I get the impression the specified beam size may be optimistic… or only represents the most intense portion of the beam. I’m curious what type of divergence you’d be getting.

I forget the exact distance now but I was asked to do a long distance test that was quite far away when doing the tem mode test. Not sure why. Instead, running the test at the lens tube was sufficient. Again, I’m cynical that this might be to help reduce signs of a non gaussian curve.