What Could Prevent an Internal Mirror Tube from Lasing?
If it has good pure argon at the right gas pressure, a working fan, the proper stable current down the bore and reasonably aligned clean mirrors it will lase. The 488 nm line will lase from .01 torr to 2-4 torr even with dirty mirrors, so it’s almost guarenteed that you will get something. I doubt there is dirt or scratches in the optics as those would not leave the factory. Where these conditions are met, the most likely explanation is very slight mirror misalignment. It would not surprise me that just applying pressure in the right direction to one of the mirror mounts by slipping a steel tube (WARNING: High voltage – use something well insulated to grab it!!) over the mirror mount without loosening the set-screws (if present) will cause the beam to pop on. It should operate once the mirrors are somewhat aligned. Tubes like the Cyonics/Uniphase have a curved output mirror and a flat high reflector. Even if slighlty misaligned, this configuration is set up to tend to correct itself op
