Hughes / Melles Griot 3121H-P Helium-Neon Laser Tubes

These tubes were gotten out of a dumpster behind the local university's biology and science department. They were all wrapped in bubble wrap and surprisingly not cracked or broken. They are all the same model and manufacturer but look slightly different and each have different dates of manufacture. The tubes all output a red beam (632.8nm) and according to documentation have a maximum output power of around 2mW. So far, 1 of the 3 tubes runs properly, the others strike but do not run reliably. The power supply being used which was obtained separately from the tubes is a Power Technology Inc. model L23120AM023752 potted brick-style HeNe power supply. The label specifies a 14-16VDC input voltage and a 1900VDC output voltage. Current is listed at 1A for the input and 0.005A for the output. The 1 functional tube with serial number 1054WW runs reliably at 14V while current limited to 1.8A. A ballast resistor is connected in series.

3 laser tubes lined up

tube on and lasing a red beam

HeNe laser power supply

Sam's Laser FAQ is a great resource for all things lasers. It proved to be very helpful in getting the HeNe laser tubes up and running.