New Optics have Arrived

I received the new optics for the CO2 laser yesterday and am anxious to try them out. I still have to finish some lathe work on the last mirror insulator and caps. Here is a photo of the new optics. I ordered them from Bruce Sunderland at (www.designreasearchoptics.com) who was very helpful with hobbiest like me who are just playing around with this kind of stuff.

I have also finished the second laser head today, I am impressed how well it turned out. Every one I make turns out a little better and quicker than the first.

I also finished the mirror insulator, I still had to take the OD down a bit and insert the mirror mount o-ring. I chose a 1/8″x1″OD o-ring for this and counter sunk it so it won’t fall out like my last design. The mirror insulators fit to the electrode heads very well and seem like they might maintain their alignment. I really won’t be able to tell until I actually get this thing to work and try removing and replacing the head… I’ll hope for the best tho.

CO2 Laser Tube

This is my first semi-successful laser tube. The first one I created used a similar design but with epoxy to seal everything together. The epoxy couldn’t hold back the cooling jacked pressure from the vacuum in the laser bore and failed allowing water to seep in. One side of the laser tube sealed just fine making me think I mush have not mixed the epoxy evenly. Sorry, no pics.
This design used 2 round pieces of aluminum and plastic which squeezed a piece of rubber to seal the cooling jacket from the laser bore. I built everything on this design to be removable and replaceable. For how often I may have to change a broken laser bore or something it was just extra work I didn’t need to do.















The metal clamp hides the rubber seal in this photo. This design also seems flawed although it works much better than the first… My new laser heads and sealing method will work far better I think as long as I take more time to precisely mix the epoxy.

New Laser Heads

I have just recently finished one of the new laser heads for my CO2 laser. I believe this design will work much better that the last. I used a 2″ piece of aluminum and designed it so it will grab the outside of an acrylic tube and the outside of the laser bore. I decided to again go with using the laser head as the electrodes, as that part seemed to work fairly well on the last design. I decided to also space the mirrors apart from these electrodes using some hard plastic material. The step on the end was to try to keep the mirror insulator centered so I can remove the mirrors without adjusting alignment, I’m not too sure how well this will work. When aligning the mirrors on the old tube I found the slightest adjustment caused a drastic change over the long 1.2m tube.















The hole in the top of the 2nd picture is where epoxy will be inserted to insulate these head tubes from the cooling water. I have bought a epoxy which is supposed to bond glass, metals and acrylic. I have tried gluing scrap material together and the outcome is promising. I drilled the fill hold with a #29 drill so after the epoxy has dried I can re-drill and tap the hold with a 8-32 screw for the electrical connection.
And a pic with showing how it will go together, using a piece of laser bore I accidentally broke.


I also spent some time with this one on the buffing wheel. Just for better looks

CO2 Laser

CO2 Laser

A little info on all the pieces that make this work.

Laser Tube
The laser tube, the piece that looks like a florescent light above is the heart of a CO2 laser. It works by exciting the atoms in the gas using an electrical discharge. The gas is a mix of Co2, Nitrogen, and Helium. The exited nitrogen atoms bump into the CO2 atoms and cause them to transfer their energy. The excited CO2 atoms will fall to their lower energy state by releasing energy in the form of light radiation. This light will bounce off the mirrors placed at either end of the tube and cause other CO2 atoms to release energy. Some of this bouncing light will escape from the partially reflective mirror and viola, you have a laser.

Vacuum Pump
To get the atoms of gas to excite you need to send a current through them. If you were to try to get electricity to flow at atmospheric pressure you would need and incredibly high voltage to get at arc started. You would need this really high voltage because the electrodes are almost a meter apart from each other. If you take out some of the pressure in the tube and then try to start an arc it will initiate much easier. This is why you need a vacuum pump. Even at this low pressure you need apx. 15,000V to get a stable arc.

Above: Cenco vacuum pump attached to a 1/2hp 115V motor.


Power Supply
To get the 15,000V necessary to get an arc across the laser tube you need a power supply. The easiest supply is a neon sign transformer or NST. The nst I have is a 15/30 which means it is 15Kv at 30mA, this is a little undersized for the tube I have built but should work for initial test purposes. I am using AC to excite the tube for simplicity although DC is really the recommended method. More on that later.






Water Cooler


The water cooler is simply to keep the laser tube cool. A CO2 laser will not function very well or at all if the gas becomes to hot. This is why helium is introduced into the laser gas. The helium will help transfer heat to the laser tube walls and then the water will carry it out of the tube. I am using a Miller water cooler for a Tig torch, as I had one lying around.






Mirrors
The mirrors in a laser are responsible to increasing the energy output to achieve a useful beam. For CO2 you have to use special materials because of the wavelength of light it emits. A CO2 laser emits light at 10,600nM which is in the far infrared band. This light is totally invisible to the human eye. Because of this long wavelength materials like glass will not allow light to pass and are essentially opaque. Materials which will transmit CO2 laser light are NaCl (Table Salt) ZnSe (Zinc Selenide) and some other semiconductor materials.

A picture at the output mirror, the partially transparent one. You can see the premix laser gas bottle in the background.