This is what the beam looks like at 12% power...I've never noticed this before

This is what the beam looks like at 12% power…I’ve never noticed this before with the other tube…or the k40 that I used to own…any thoughts anyone.

It’s almost a perfect doughnut shape. What is the lowest power you can shoot at? I’d be interested to see the difference in beam shape for different power %s to see if the dead-spot increases in size at lower powers or at higher powers.

I’d expect the elements in the laser tube are out of position, causing exactly what Yuusuf described, only in the tube optics instead of the head.

That may be why the larger tubes use externally adjustable optics.
Pretty hard to hold all those elements in just the right place while your glass cools…

@Scott_Marshall That being said, is there a lens/optics set-up inside the tube?

@Yuusuf_Sallahuddin_Y …that is the lowest power setting that it will fire at…
12% power.

Yes it’s ALL inside. The mirrors are concave, and focus on one another, which keeps the beam straight and minimizes scattering losses.

If they’re off by even a few thousandths, over 3 feet, it’s a big error.

Remember the light has gone back and forth a few million times by the time it hits the tape…

@Scott_Marshall …I think you guys are right…nothing I can do about it…I’m gonna run the mess out of until it quits them reinstall the reci tube.

@Yuusuf_Sallahuddin_Y …at 20% you can’t see the dead spot at all…crazy right.

In the tube there are just two mirrors…one fully mirrored and one 90% mirrored…I think that is correct.

@Scott_Thorne That is odd that increasing the power removes the dead spot. So I guess, just don’t run under 20% haha.

@Scott_Marshall I’ll have to take a closer look at my tube. I’ve been wary to even look at it in case I break it just by looking haha.

Yep, here’s the workings
Ophir again…

Look at the Spherical Mirrors (it’s for a beam expander, but the principle is the same) pictorial and imagine what happens if the mirrors are off and beam out is not precisely swept by the beam in mirror, no center fill, instant ring.

About looking at your tube,
I doubt you’ll be able to see the error, it’s so tiny to detect it you’d need a good optica lbench and know how to use it. Or turn it on…

Looks like your laser is running in TEM01 mode instead of TEM00-

Unfortunately that kind of operation is inherent to the optics in the tube (primarily Brewster angle of end plates), so you can’t do anything short of replacing the tube.

@Scott_Marshall I meant I wanted to look at my tube to see if I could see mirrors in it. I honestly don’t really know how it works as I’ve barely looked at the tube itself. I only really have that doughnut looking ring when I deliberately defocus my beam/material.

Good views of a tube here (full screen it)

This could be a “second” sold as a first. Second is a product not perfect.

It probably is @HalfNormal …I may have been duped…only paid 225…but it works good…cuts good…engraves good.

@Scott_Thorne As long as you are happy with it, that is all that matters. I always look for the bargain and hope it is not a total dud!

@HalfNormal …amen brother…it works great at normal power…I just noticed the anomaly when I was aligning it…but to be honest the reci tube that was in here might have done the same thing at extremely low power…if it did I never noticed it.

I’m not hitech but i would be thinking that it is about how beam form in tube. And that it not fully form and saturate fully with low power.

I’ve had the same pattern on my machine too, only happens at lower settings too. I just assumed it was normal :\