When the tube lases, it resonates between the mirrors inside the tube. As the gasses degrade this resonance changes and the output beam changes. This is not user serviceable. Sorry… I had to change my tube out because of this… This is how mine started to degrade… It was dead center… It seems to move and a re-alignment is needed if you want to keep using it. As it got worse, the results on the outer corners varied.
Don’t know if that’s your case, but you have enough of the indicators to prompt me to ask.
The tubes output is what you want to see… this is before any mirrors… Here is a photo I sent you a couple weeks ago… it shows the target setup for TEM determination and the targets I cut out for use in alignment of the mirrors…
