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.