This one is a late '60s Perkin-Elmer model 5600 He-Ne system with a model 5204 power supply and adjustable mount. It came to me with the model CD1 centering detector and meter also shown below.

The head includes a collimating lens on the output end and I assume there's a diverging lens inside, but didn't want to disassemble the head to find it. The centering detector has separate silicon quadrants. My guess is that a fatter beam gave better resolution on the meter. I'm amazed at how crooked the labels are. I hope they fell off and were put back on by a slob. Anyway, I may heat them up a bit and see if they come off so I can straighten them out.

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