Beam Shape / Pattern

I’ve noticed when I’m aligning that the beam pattern when I’m close to the emitter… between 50-70cm away I’m getting an odd pattern on my thermal paper when I pulse. It looks like an “O” instead of a dot. Sometimes a crescent. Once I move 70cm or more away it seems to come down to the more expected point. Is this normal? Sign of tube degredation? Something else? Why would the beam pattern look hollow in the middle and then change with distance? I would love to learn more about the physical properties of why the beam is as thick or shaped as it is. I know energy falls off with distance but I always assumed a laser’s shape was a consistent column of light.

I’ve cleaned the emitter end, replaced all the mirrors and I get this output directly from the emitter without hitting any mirrors, as well as after bouncing off mirrors. This is a 130w continuous rated 170w peak tube (168cm long) only a year and a half old or so. My process has been to pulse at 11% max power using thermal paper.

Not an answer but an opinion:

I think 11% power for a 130W laser is borderline for the tube to trigger properly (not forming the beam), up the power slightly and the trigger voltage should work correcly.

Thermal paper is also extremly sensiitive so will record a mark even if the voltages are in a unstable state.

Cut off for consistent tube fire on this machine is 10.2%. If I go much above 11 I get too broad a mark for alignment. I prefer the sensitivity of the thermal paper as it really allows me to pinpoint laser position when I’m greater than 70cm from the emitter tip at least.

Please avoid posting the same question across multiple threads:

Sorry, I digressed a bit on this thread, was trying to give context to what I was trying to figure out. They were genuinely intended to be discreet questions.

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