Arcing and sparking in laser tube

Hi all, I’ve had my 40w laser for about 3 years, only used it sporadically up until about a year ago when me and my girlfriend set up little etsy shop. We replaced the original tube after it broke about 3 months ago (we hadn’t been clearing the air bubbles, lesson learned!) and the new one seemed to be working fine. The laser stopped cutting properly and we noticed a general drop in power. There seems to be a kind of arcing going on at the negative end of the tube when it’s running and we noticed a spark at the positive end with a clicking noise which seems to be coming from the power supply.

I’m not sure how to proceed so any help would be greatly appreciated.

Can you post picture/video of:

  • The arching (video) at each end
  • Your control panel.
  • Your laser power supply showing the connectors

Thank you for taking the time to help me out Don, hopefully these images are good enough.

I was expecting to have to wire the new tube in myself, but when it came each end had a wire already attached and I just spliced the wires in.

The movement of the beam in the tube at the anode and cathode looks normal to me.
I do not think they are arching.

The beam looks healthy and I did not hear any clicking.

Have you checked alignment, cleaned mirrors and lens?

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Thanks Don it’s a relief to know that the movement is normal. The video doesn’t show it very well but there’s a little spark on the inside of the left side of the tube (the anode side?). It seems to be arcing into the metal ring inside the tube. I’ll try to get a better video of it.

I cleaned and aligned all the mirrors and lens and replaced the coolant with some fresh distilled water before posting here sadly. I was really hoping that would solve the issue!

Is this the arch you refer to???
If so it looks to me like it is just igniting the plasma i.e. normal.


It’s hard to know what the LPS is doing as you have no MA meter [right?].

You could try turning out the lights at night and observe the LPS and tube to see if can detect any arcs outside of the tube.

My guess is still that there is an optical problem.
Post pictures of burned targets at each mirror and then on the bed at the focal point.

Thanks Don, sorry for the late reply I’ve not had much chance to get in the workshop lately, the day job’s getting in the way.

I’ve been looking into it and it seems like my alignment isn’t quite right on the final mirror. All the burn spots are in the same place near and far but it’s a little off centre going into the lens. I’m going to try adjusting the laser tube position and check everything’s square.

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Just to make sure you have resources easily available for alignment, and in case you haven’t yet found this, from K40 initial setup and regular maintenance: Alignment

The path that the laser takes along three mirrors and the lens needs to be precisely aligned. Here are three resources that may help you understand how to do this.

If you prefer video instruction:

Ep6: Laser Beam Alignment. The DIY CO2 Laser Cutter / Engraver Build Series

If you prefer written instruction, here are two guides:

Note that if the third mirror does not align the beam with the middle of the lens, the beam will not be focused correctly and will not be aligned with the hole in the nozzle. You may wish to use a device that helps you align using a red visible laser. One kind uses a “beam combiner” that slightly reduces beam power, and the other is a tool used only while performing alignment .

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Thanks for all your help, that’s an excellent resource. We just needed to reposition some of the mirror mounts and raise the new tube slightly. The beam wasn’t hitting the centre of the lens properly after all.
It’s working great now.