First Homemade CO2 Laser Built From Scratch
This webpage demonstrates a DIY laser built from scratch, using a balloon and needle valve to supply gas to an electrical discharge. The laser will run on a mixture of helium, CO2, and nitrogen, or it will run on ordinary exhaled breath! Helium only enhances laser performance. CO2 and nitrogen are the only two gasses that are absolutely required. The laser will run with air that is simply exhaled into a balloon, because there is both nitrogen and CO2 present in the air that we exhale. In order to do so, I hold my breath before exhaling into the balloon, allowing my body to replace more oxygen with CO2 than would occur if done quickly.
If I'm using an actual gas supply as opposed to just running the laser on my breath, I first deposit a small amount of CO2 into the storage balloon (hereafter abbreviated as SB). I measure the circumference of the SB using a tailors measuring tape, and then use this circumference to calculate it's volume. After considering the volume of CO2 that the SB contains (I want the CO2 to be about 10% of the final mix), I decide how much N2 I want in the mix. If I want roughly twice as much N2 as CO2 in the final mix, then I add this corresponding volume to the volume of CO2, and calculate a new circumference (in other words, 3x the volume of CO2, which I originally calculated). I then fill the SB with N2, until I arrive at this new circumference. At this point, I divide the sum of the two volumes by 30% (assuming I have twice as much N2 as CO2), and then calculate a final circumference using this number. Following this last step, I inflate the balloon with helium until this final circumference is reached. In this way, the 3 gasses can be combined in a predetermined ratio with some accuracy. Sure - the balloon is not a perfect sphere, but this method is much more accurate than simply guessing!
Helium can be obtained at Walmart in the form of a party balloon kit - cost around $20. Air should be fine for nitrogen, although welding nitrogen would probably be better if available. CO2 can be obtained from dry ice, or by mixing baking soda and vinegar.
Here are some photos that show what happens when the invisible laser beam is focused onto the surface of glass. The glass becomes so hot that it glows with white incandescence. The surface melts. If the laser beam is held into position long enough, the glass will either crack due to thermal expansion, or a hole will be burned through the glass.
Carbon absorbs a lot of optical energy, and reflects very little of it. The two pictures below illustrate this. In the photo on the left, a piece of artist's charcoal sits in front of the laser. The photo on the right shows what happens when the laser is switched on: when focused onto the charcoal, the invisible laser beam heats the charcoal to blinding incandescence.
Wood makes a good target for the beam, and it can often be set on fire without the need for focusing optics
When unfocused, the beam usually causes wood to ignite, or it causes the charred surface to glow red like the tip of a cigarette. When focused onto wood, however, the charred surface appears to respond like artist's charcoal: a tiny point of brilliant white light is produced.
The construction of my first successful CO2 laser began after someone gave me some spare glass tubing. Shortly afterwards, someone donated some ZnSe optics. It was at this time that I became really serious about building a working CO2 laser.
I have looked at both the Scientific American and Information Unlimited plans for this type of laser, but the best resource for individual experiences with this device can be found in the home built CO2 laser section of Sam's Laser Faq at http://www.repairfaq.org/sam/lasercc2.htm#cc2toc
I did not follow exact plans to build this laser. The dimensions are mostly arbitrary, based on the parts that were available. The builder can look at various plans and online sources of information, and can then arrive at a general idea of the range of different part types that will work. For example, a high gain laser like pulsed ruby can be used with mirrors that are not designed specifically for it. On the other hand, there are few common materials that will transmit the long wavelengths that are produced by a CO2 laser. With some creativity and a general understanding of the device that is being considered, the builder can construct a laser using the supplies that are easiest to obtain. It is better to understand enough basic principles to enable flexibility when needed. This can save time and money!
My laser began with a 4 foot section of neon sign tubing. The tubing has an ID of approximately 1cm. For a water jacket, I used a section of fluorescent lamp protector tubing, which is a flexible clear plastic tubing sold to place around cylindrically shaped fluorescent bulbs in order to protect them from accidental impact. I do not recommend using this tubing for anything other than a short laser tube: the reason is that is bends and flexes when water is flowing through it. Glass would be ideal, but irregardless of the type of tubing that is used for the cooling jacket, the construction details given below should still be applicable.
I began by building up a layer of masking tape around the outside of the neon-sign-tubing. This tape is positioned at an arbitrarily equal distance from both ends of the glass tubing. The distance between the two tape rolls will define the area through which the water coolant flows. I gradually built up the tape layers until they fit the ID of the plastic cooling jacket. After this step was complete, I began building up a thin layer of JB weld epoxy along the sides of the tape cylinders (see below).
The tape 'method' did not originate with me. This approach is suggested in the CO2 laser plans from Information Unlimited. However, I have found that the tape method will adapt to a multiple set of circumstances. It can be beneficial with anything that involves centering one cylinder around the outside of a second smaller cylinder. It can be used to join parts that would otherwise be incompatible. Although not perfect, I have used it to fit the tiny output shaft of a small DC motor to the relatively large hole in the center of a CD, when making a small motor driven electrostatic generator. So it can be a reliable method to enable flexibility where a limited variety of parts are available, and where limited tools and funds are available for better alternatives.
Although the tape method is not my own idea, it was my idea to use masking tape for this purpose. Unlike some of the other common types of tape, masking tape is cheap, and it combines evenly as it is rolled onto a cylinder-shaped surface. Once complete, the masking tape roll can be coated with epoxy and sealants in order to provide strength and protection. I coated my entire tape roll with JB weld, and then sealed the outside with shellac. See the pics below for an example. As you have probably noticed in the previous photo, there is a seperate tape-wrap on the tip of the glass tubing. Although it is a bit premature to mention this, it will eventually serve as a spacer to couple the outside of the glass tubing to the inside of a section of copper pipe, which will serve as one of the two discharge tube electrodes. For now, ignore this step. It only became necessary for me to mention, in an effort to avoid potential confusion.
Once the epoxy and shellac were dry, I slid the clear plastic tube over the tape roll. Keep in mind that there was an identical tape roll on the opposite end of the glass tube, and the larger plastic tube was cut in length to match the distance between the outer edge of one tape roll and the outer edge of the other. After the tubing was slid in place, I marked two spots on the outside of the plastic tube with a Sharpie marker, a short distance from the inside edge of both tape rolls. The two spots were marked 180 degrees apart from each other, as determined by the outer circumference of the plastic tube (judging by eye). Small holes were drilled through the locations indicated by these Sharpie-spots, and two 1/4" hose barbs were secured over the holes using JB weld epoxy.
After the water jacket is complete, test it to confirm that there are no leaks! This is very important. Water and high voltage obviously do not mix! I bought
a small water pump from a local hardware store. These pumps are used to continuously circulate water for small fountain displays: the small decorative kind
used in back yard or small indoor water falls. Use the pump to circulate water through the cooling jacket. In this way, you can spot any leaks that appear,
and fix them as needed with additional JB weld. Once all the leaks have been sealed, and the tube has been thoroughly tested with no additional leaks, then you are ready for the next step.
The next major step involves construction of the end piece electrodes. My first such device used 2 nylon washers, a rubber gromet, a section of 1/2" ID copper pipe, and
some copper tubing.
This is where you will have the opportunity to benefit from one of my mistakes. Nylon washers were the largest type of washer I could find at the time
the original end pieces were constructed. I thought that by doubling them up in pairs, I could provide enough strength to withstand the exerted force required
during alignment. I was wrong! So ignoring the fact that these end pieces are nylon, look at the following picture for an idea of how the end pieces are
constructed.
Aside from the choice of nylon washers, there is one additional part in these two pictures that is unecessary. This is the shiny round metal part near the middle in the
first photo, and the shiny metal part that protrudes to the right of the nylon washers, in the second photo. This is a part of the original design that I
decided not to use, and for now it is irrelevant. However, the 3 bolts are very important. It will be necessary to drill 3 holes through all washers, and then
JB-weld three compatible nuts (nuts that go with three corresponding bolts) over the holes on the side with the copper pipe (see photo above). I recommend the use of metal washers. The next steps of this tutorial will
show metal washers, which I ended up switching to when I realized that nylon was too flexible. But for now, refer to the photos
above as an example, knowing that the final device (if you are constructing it) will need to use metal washers instead of nylon.
To one side of the 1/2" ID copper pipe, I drilled a hole and soldered a short section of 1/4" OD copper tubing. This will become a hose barb. In reality, an
actual hose barb would have worked here. However, I chose to use the copper tubing because it was both avaliable at the time, and was compatible with soldering work.
JB Weld will probably do here, but be sure and first sand and thoroughly clean all parts to which the JB Weld is to be applied. The dangling hoses that will be attached to these
hose barbs will exert some stress on them, due to their length, location, and inevitable movement. It is from these hoses that gas will be fed into one end
of the laser tube as air pressure will be drawn out of the opposite end by a vacuum pump.
Some detail of end piece construction is shown above. Most of my work was done using JB weld, but the builder might prefer to use solder, brazing, or welding
provided these resources and skills are readily available. Either way, the idea is to get a metal washer centered around a short section of copper pipe. The
pipe can be about 3 or 4 inches long. You want washers that are big enough so that you can drill holes and mount the adjustment bolts and screws near the
outside edge. At the same time, you want the inside hole to be as close as possible to the diameter of the outside of the copper pipe. My approach was to
combine smaller washers with the larger ones, in order to more easily couple everything together. The pictures below show how small washers can be combined
with larger ones, in an effort to make the hole in the middle 'smaller' so that it will come closer to fitting around something that will pass through the
center. Look at these pictures very carefully, but be aware that they are used only as an example. A range of different sizes can work. The deminsions of
these parts should be based upon availability, and how easily they can be adapted to the other parts (like the copper pipe) that you are able to locate.
As you might have correctly guessed, the arrangment above was used in the construction of another laser project. It is very close to what you will be doing (and what I did) for the laser that is covered on this page. Building up layers of tape and using multiple sized washers basically does one thing: it allows the large washers, which are really the most important part of the mirror mounts, to be custom fit and centered onto the electrodes and the actual resonator mirrors. The glass tube that serves as the actual laser bore will be the heart of the whole arrangment. You must design your laser around this glass tubing. The tube is the most important part. The tube can be anywhere from a few millimeters to 1 inch in diameter. Mine is about 1cm to 1/2" in ID. So after you first obtain some glass tubing, you will then need to obtain electrode 'pipes' that can be fit onto the ends of this tubing with reasonable effort. To better clarify, please refer to the pictures below. These pics show how the 'pipe' electrodes were custom fit onto the ends of the glass tubing, with mirror mount (washers) already in place.
As you can see from these photographs, the tape spacer couples the glass tubing to the copper pipe. By looking at the cooling jacket, you can tell that these pics were made before the JB-weld was applied to the jacket. When I built this laser, I did not plan to make a website. As a result, I did not carefully photograph each step in sequence. This is why I am having to 'borrow' examples from other projects in order to provide a semi-complete illustration. I'll admit that this is not very well organized, but next time I will be able to plan beforehand, and take pictures of each step as I go for better clarity. I also made some mistakes in the construction of this first laser, and unfortunately these mistakes are included in the photos. The nylon washers are a good example of this. As a result, I must keep going back and forth between pictures of the actual laser, and pictures of something else that illustrates how it should be done. Please accept my apologies.
Now you want to wrap some masking tape tightly around the outer circumference of the washers.
It is important to remember that the washers are arranged into pairs, with each pair having the flat sides facing (the individual washers should have one side that is obviously flatter than the other side). Because the holes might not be precisely 120 degrees apart and precisely positioned at the same distance from the edges, you will want to keep the individual pieces from getting mis-matched; in other words, you will want to keep four pieces paired as they were when you drilled your holes. To avoid getting them mixed up, I marked one pair as "A" and the other as "B". This will become important when these washers are fixed to the end pieces that they are being designed for. Aside from keeping the washer pairs seperate and consistent, there is also the need to keep them from becoming rotated away from the position that they were in when the drilling procedure was performed. To ensure that this detail is not overlooked, I marked one of the three holes, on all four washers, with a sharpie. This enabled me to ensure that these holes were lined up radially in the same way that they were during the drilling process. See the picture below for an example of this
The next step involves the adjustment bolts and threading. You will want to sand and clean one side of one washer, from each of the two pairs. Because the two flat sides were positioned facing each other when drilling the pairs, you will want to sand one of the curved sides (as opposed to the flatter side) on the piece that you choose from each of the two pairs (see below).
The side that is sanded will eventually face the glass tubing that extends from one electrode to the other. Take one pair of washers and insert three hex-head bolts through the three pairs of holes. Tighten three nuts onto these bolts, on the sanded side of the washer pair. Apply JB-Weld epoxy around these nuts, allowing the epoxy to come in contact with the sides of the three nuts. Be careful not to allow any of the epoxy to get onto the bolts, on into the threads. All surfaces to which the epoxy is to be applied must be free of oil and dirt, including the nuts. Before applying, soak the nuts in alcohol to remove any oil or grease residue. Allow the nuts to dry before applying the epoxy.
Once you have two pairs of washers that fasten tightly together using six hex bolts, then you are ready for the next step. The holes in the middle of my washers were much larger than the outside diameter of the copper pipe sections used for electrodes. The holes were also significantly larger than the outside diameter of my resonator mirrors. So I needed some way to 'step' these holes down, before taking up the slack with the tape method. The tape method would probably be acceptable for creating a spacer between one washer from each of the two pairs, and a corresponding copper pipe electrode; but I preferred something with a smaller profile for the purpose of mounting the resonator optics. Look at the picture below. You will notice that a small additional 'insert' washer was placed over the center of the larger washer. This 'insert' washer takes up the space between the larger washer and the tiny output mirror.
Below is a diagram showing the basic setup. The output mirror must be in line with the opening of the copper pipe. The three adjustment bolts are tightened against an O-ring. The O-ring serves as both an air-tight seal, and resistance against which the bolts are tightened seperately to provide mirror alignment.
Once the basic structure is complete, you will need to apply a source of vacuum in order to check for leaks. This is where the frustration can begin. If your tube is sufficiently sealed against leaks, you should be able to create a glowing discharge within the length of the glass tube using a neon sign power supply. The distance between my electrodes (the arc length) is about 48 inches, and I am using a 15kV, 60mA neon sign transformer. When you pull the pressure down using your pump, the tube should look like a neon sign when power is applied, except not as bright. Instead of the brilliant orange light characteristic of neon, the tube should produce a pink discharge. The glowing discharge should appear to fill most of the tube cross section. If you obtain a weak purple discharge that is brighter near the ends of the tube, then you have leaks. The weak purple discharge (or complete lack of discharge) indicates that the pressure is too high for the voltage that is provided by your power supply. Under these circumstances, the system will not work as a laser.
For leak detection, I use a fish tank air pump. I pump air into the laser tube using one hose connection at one end of the laser tube, and I seal the other end which is intended for the opposing hose connection. In this fashion, air from the tiny pump is forced into the laser tube and out through any leaks that are present. Using a small brush, I apply soap water to all joints and surfaces of potential leakage. Leaks will be indicated by bubbles which form after the soap water is applied to a suspect location.
