Big Ass Laser - Our Laser Cannon project!

Yes, we have a laser cannon. It is really big. In a previous life, it was a medical laser. Now it is a 240 Watt Carbon Dioxide (CO2) Cutting laser. Well, almost. More like an ongoing project, with a near-term goal of melting bricks. Carbon dioxide lasers emit (far) infrared light, which is unfortunately not visible to the naked eye.

History

About 1993(?), A large medical laser turned up at the UCI salvage yard, for sale for scrap. Three of us decided to buy it, and split up the parts, I wanted the HeNe aiming laser, control electronics, and pnuematics. Mark wanted the low voltage DC power supplies. John wanted the laser warning signs, and anything else left over. I ended up with almost all the guts, but being a salvage operation, just hacked everything out. Therefore, the main component missing was the wiring harness. Only months later, the realization dawned that it could be put back together, if I had only taken some notes on the wiring... DoH!

Over the next couple of years, I started to reverse engineer the electronics, to figure out how to control the massive high voltage supplies. But incentive was low, and other projects took precedence. The pile of components was used more to scare friends and coworkers... Yes, it really is a big laser. Really Big.

Then I met Erik, around 1996(?). He was a bright young high school student hired on at work to help out. He was VERY intrigued by the laser, and tried to get his school to buy it for a class project. He never could convince all the right people, and eventually graduated. I looked at more of the parts, and helped him try to track down all we could on the history of the beast. The first 14 or so pictures below were part of that effort.

March 1998. After moving all the laser parts a THIRD time, it was loosing the battle of value vs. space occupied... it took a lot! I told Erik if he still wanted it, to come get it! He did, and it has been living on his dining room table until recently.

June 2000. Erik has cleaned up most of the mechanical components, replaced the crumbling gas line tubing, and tried to figure out all the plumbing parts. I unearth my stack of notes and reverse engineered schematics, so we rekindle the project. Together, we figure out the way all the plumbing and gas lines were connected, and the function of all the valves and filters.

I finish mapping out the I/O card cage boards, and start a memory map of the I/O ports. Start mapping all the wires coming out of those boards... almost 70 total.

July 2000. Mark volunteers to return the DC supply to the project. That sparks construction of the new and improved control panel [from hell!]. The plan was to get the original controller working, but have all the wiring hit barrier strips first, so it is easy to change things around while we figure out how it all goes together. The second half of the design was to have a panel of switches anb indicators to manually override the controller, or override it's inputs to make it happy. The convienent list of fault codes on the display provided an easy way to identify several sensor inputs... start shorting wires until the fault clears! See pictures below! This technique worked until I got to the cooling system. I have not yet found the proper combination to clear this fault.

January 2001. Holidays provide more time for experiments and research. I start testing parts of the HV supply under controlled conditions to figure out how it works, I just need a few more details. There is a single wire (the infamous "purple wire") that I was not positive of its function. I had a good theory, but wanted to prove it before putting 20,000 volts on it!

To figure out the startup sequence (and what the stupid cooling system fault is complaining about!) I read in the EPROM and put it through a Z80 disassembler. This resulted in about 4000 lines of assembly language. It also revealed a maintenance mode accessed through the serial port, with about 18 commands! Several weeks of work later, I have about 50% commented, and most of the startup sequence mapped. This led to the key sequence to enter the maintenance mode. There is something funky about the serial port, when trying to use it, the CPU hangs somewhere around printing the banner, sometimes printing it all, but not very often.

On the other end of the wires... Erik bought a tank of laser gas, and a regulator. We moved the head, cooling and vacuum systems out to his garage.

January 14, 2001. First Test firing. Hooked up the traditional variac and Neon sign transformer to try out the tubes. There are two tubes, that are coupled optically in series with a pair of turning mirrors (the tubes are parallel). Each tube has three electrodes, positive in the center, a high voltage terminal at one end, and a grounded terminal at the other. The two HV power supplies have two insulated output pins, and are actually dual supplies. One half powers the half of a tube between the two HV terminals, and the second half powers the half beteween the center and the grounded end. My guess is the mystery purple wire connects to ground, in such a way as to measure the tube current.

We pull down the vacuum, start the gas flowing, and start cranking up the voltage... purple and pink glow! After messing around a lot with HV connections... and finding the transformer has a center-tap grounded secondary, We can get a whole tube lit. The problem, is they two halves are in paralell, so when one strikes, the other does not have enough voltage to strike. Makes a neat effect when the arc swaps back and forth from end to end several times per second. We end the night with a decision to add some ballast resistors while we wait for two more transformers that have been ordered. We did get a good glow in parts of the tube, at various pressures. However, we never got sigificant IR power out. This makes us sad, because it could be many things wrong... gas, pressure, voltage, current, contamination, bad mirror, one (or more!) of the four mirrors out of alignment...

January 21, 2001. Test firing number 2. My ballast resistor network was not sized properly, and did not last long... way over heated. Back to the calulator and resistor box. We also tried the second tube this time, and were relieved that it has a nice glow also. As a test, we skipped the center electrode, and energised from end to end. This produced a nice stable glow, and even passed some yellow light out the output coupler, with dim halo around a 1 inch spot. This gives us hope... looks like the mirrors are doing something. An interesting side effect of driving the tube this way... the gas line from the HV end runs parallel to the sheilded HV lead (grounded sheild) so the gas in it was ionized and glowing all the way down to the fitting at the grounded end. Check out the pictures my brother took!!!

Here are some pictures of the main parts, and my new control panel, and the original controls.

	Top view of the head		turning mirror end of head, with cooling plumbing
	Output apeture mirror assembly on head		entire head unit
	Vaccuum pump		Cooling pump, reserviour, and radiator/fans
	Other side of whole head unit		the three main controller boards: CPU, and two board IO interface set
	The cpu board, that actually lives inside the back of the control panel		CPU board
	Control Panel		HV power supply (one of two)
	output shutter and mirror assembly		Closeup of a HV power supply, 100VAC input on left, control I/O in the middle, and HV out on the right.
	New control panel		Top view of new controls with all wiring broken out to barrier strips
	Original control panel		Sticker on top of control panel showing fault codes, gas mixture and manufacturer.