Hand machined mechanical pencils

RF CO2 laser head (30/03/10)

This is a folded-resonator carbon dioxide laser I came by a couple of years ago. I eventually got around to cutting it open to see what the innards are like. I don't have the means currently of actually running it, but it looks to be in excellent condition. It is probably quite a powerful laser, since the total cavity length is over 2m - I'm guessing it would be capable of several hundred watts of output power.

Here's some photos of the laser, with comments:

Output end of the laser. The orange disc is a ZnSe window.

Rear end of the laser showing the two high reflectors. Note the weld around the rim - this was ground off to allow the insides to be drawn out of the tubular housing.

Both rear reflectors removed.

Rear mirror cover and high reflectors. The mirrors appear to be coated silicon.

The guts of the laser.

Rear end of the cavity. Note the white ceramic piece - this contains the channels for the plasme and is sandwiched between two aluminium electrodes, the bottom one water-cooled.

Front end of cavity. The small inductors placed in parallel with the electrodes form a resonant LC circuit with the electrode capacitance, so the tube can be driven efficiently at resonance.

View looking down the cavities.

Electrodes and cavity CAREFULLY removed.

Bottom electrode (water-cooled). Note pattern on surface.

Bottom electrode, near the middle.

Some shots of the ceramic cavity. Note the two channels.

The "Z" shape of the cavity can clearly be seen.

Crossover point in the middle.

Another view.

The Z-resonator structure provides a very compact means of getting a long cavity length out of a short laser structure. Aligning it is probably a bit more difficult since there are four mirrors to adjust (three high reflectors and one output coupler). As for driving it, the laser appears as a parallel LC resonant load and so it can be driven at resonance with an RF power supply. Frequencies are typically in the 10-20MHz range, so nothing too drastic. In actual fact, Synrad publish driving circuits for their lasers (these are available in the user manuals) and they look surprisingly simple - nothing more than a single-MOSFET oscillator with some feedback from the laser head to keep it locked on resonance. So, if I ever have a free couple of months and a big tank of laser mix, I might give it a whirl!