Looking through eBay recently I came across a great deal on some Helium-Neon laser heads from Melles Griot. While definitely not new, these gas lasers are extremely long-lasting & I figured the tubes inside would make a nice addition to my laser collection. Doing some searching on the model number, these heads are rated at an optical output of 4mW, but depending on how much milage is on the tubes, the output may be a bit higher.
I got a pair of the heads, this one was manufactured in July 1988, the other March 1989.
The OC end of the head has the laser classification label & the beam shutter. Once I’d tested the laser heads to make sure they survived the post intact, I set at extracting the plasma tubes from the aluminium housings.
The end caps are fibre-reinforced plastic & are secured with epoxy resin, so some heating & brute force released the caps from the housing, giving access to the laser tube itself.
The laser tube is secured in these heads by hot glue – this was squirted into the housing via two rows of holes around the ends. (Some are secured with RTV silicone, which is substantially more difficult to remove).
I’ve no photos of the actual extraction process as it’s difficult enough as is without at least 5 hands. A heat gun was used to warm up the housing until the glue melted enough to slide the tube out of the housing. Since everything was hot at this stage, a piece of copper tubing (above), was slipped over the OC mirror mount, so I could push the tube out of the housing while the glue was soft. This also protected the mirror from damage while the tube was being removed.
After a few minutes of gentle pushing while keeping the housing hot, the tube was released! It’s still pretty well covered in the remains of the hot glue, but this is easily removed once the tube cools down to room temperature with Isopropanol. The line of Kapton tape running down the tube to the cathode end is insulating a start tape electrode, which is supposed to make the laser strike faster on power-up. Instead of being metal though, the electrode appears to be a carbon-loaded plastic tape.
Here’s the HR end of the tube, which also serves as the high voltage anode electrode. The start tape is clipped onto the mirror mount, but all this will be removed.
The OC end of the laser, where the beam emerges. What I think is the mW rating of the tubes is written on the end cap, probably from when the tubes were manufactured.
Applying power from a He-Ne laser PSU confirmed the tube still works!
