K40 arc / 2 dots [New to CO2 lasers, need advice]

Hi guys,

Recently bought a K40 and once it had been delivered I started the allignment proces, which went good. I hit almost dead centre in all positions (after tweaking), at the end of the proces I started to notice that instead of 1 burnmark i got 2. Traced it all the way down to the tube, so the tube produces 2 dots…

Also when firing the tube, the beam seems to arc towards to anode at the end of tube, I made a video of this, is this normal? Are the 2 problems related at all?

link to video: https://mab.to/n5qGjC2iW

Your help is highly appreciated!

I run (cooled) distilled water between 14 and 17 degrees celcius (which is optimal, with my knowledge)

Just yesterday we had this post in which two people report a similar problem with new tubes.

This looks to me like the tube is operating in TEM01 ­— that can look like two dots or like a circle. You can search this site for TEM01 to get more pictures to compare, if you like.

If the tube was delivered like that, I hope the seller will replace it. The cheapest lasers arriving with tubes that run in TEM01 has been reported to be a problem in the past. The fix is only to replace the tube, sadly.

After reading other articles this is also my conclusion, it wasn’t delivered like this because I did the first part of the allignment proces with a single burnmark. I estimate that I fired around 10 test fires, and after that it shifted to TEM01. The only way this could have happen that I received a tube near end-of-life. Unfortunatelly I do not own a measuring device, maybe also buy one even though they aren’t cheap.

I contacted the supplier this morning, explained what happend, hoping to receive a replacement tube. No answer yet (understandably).

It still leaves me with the question about the arcing inside the tube to the anode, is this normal?

It depends on what you mean by arc. (post picture)
If it looks like an electrical arc then that is not normal and can be the result of a bad tube.
If it is the plasma moving position around the anode that is normal.

In any case seems your tube it bad.

This is what I mean:

For the most part, there is a solid purple beam, but near the end, it get’s bent to the anode, this is what i mean with arc, is this normal? Ordered a new tube, but want to know what is normal/ not normal. Thank you!

I am pretty sure it normal for the plasma to jump around on that ring while fireing.

I had a similar problem after 10 hours of good operation. Turned out there was an air bubble exposing about 30,% of the anode. Replaced the tube and reoriented the water exit as a high point. No more bubbles or problems.

1 Like