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Introduction to Built CO2 Laser
The carbon dioxide (CO2) laser is the powerhouse for high tech industrial cutting and welding of metals and many other materials. Small CO2 lasers are used for marking of metal, wood, and composites, and in medicine and surgery. Even a 'small' CO2 laser produces 10s of watts of beam power and the largest are in the 100 kW range!Its output is at 10.6 um (10,600 nm) or mid-IR. This wavelength is about 10 to 30 times longer than the other lasers under discussion and often considered a source of a heat beam than a light beam. At this wavelength, normal glass and plastic optics are either too lossy or totally opaque so alternatives must be found both for the end-mirrors and any other mirrors, lenses, or prisms required by the external optical setup. Divergence/diffraction effects are also increased by this same factor so obtaining a collimated beam is also more difficult.
Many common materials including wood, paper, plastics, composites, and properly prepared metal surfaces absorb quite well at this wavelength so the CO2 laser makes an effective marking, cutting, welding, and heat treating tool.
See the chapter: Carbon Dioxide Lasers for more information on the characteristics and applications of these devices.
It is possible for an amateur to construct a working axial flow CO2 laser (non-sealed, see the chapter: Carbon Dioxide Lasers) in the 10 to 50 W range without too much difficulty - at least compared to some of the other types of lasers described in this chapter. A vacuum system is needed but he range of operating vacuum is modest - 10 to 100 Torr. And while several gases are needed, the purity of the final gas fill isn't nearly as critical as for, say, the HeNe laser, and pre-mixed gas is readily available. See the section: More on Obtaining Gases.
With a bit of resourcefulness, no fancy glass work is needed. The power supply can be just a neon sign transformer on a Variac. The required mechanical precision isn't as great either so even if your machining skills are quite limited, adequate mirror mounts and structural components can be fabricated relatively easily. And, unlike the other traditional gas lasers (HeNe, Ar/Kr ion, HeHg, CuCl/CuBr, and the like), once constructed and aligned, the CO2 laser requires minimal maintenance and can potentially be a useful tool for real applications IFF it is packaged appropriately and provided with essential safety interlocks and protection devices. In fact, some commercial axial flow CO2 laser are just refined versions of what an amateur can build. See the section: Descriptions of Typical Small Flowing Gas CO2 Lasers.
My only complaint about CO2 lasers in general are that the beam is totally invisible and boring in some ways. :Otherwise, it is nearly the perfect choice for a home-built laser - high power, continuous operation, and relative simplicity!
More on the Effort Required and Recommended Power Output
The following comments should be taken in a positive way in an attempt to head off a disappointing experience for someone who really hasn't caught the amateur laser construction bug.Although, constructing a CO2 laser is easy relative to other types of lasers, it is still NOT easy in an absolute sense. You will have to make a very considerable commitment of time and effort including dealing with the frustrations when, as is inevitable, some things don't quite go according to the script! The costs in $$$ can quickly become significant as well if you don't already have any of the supporting equipment (e.g., vacuum pump, power supply components) and aren't a first rate scrounger. :)
If all you want is a reliable working laser, save your money and buy a used CO2 laser system. Something similar to what you will be building can probably be acquired for under $1,000, perhaps less depending on your resourcefulness and luck. For example, see the section: How to Get a Laser Without Really Trying - Part 1. If you can afford a bit more, try to find a sealed tube CO2 laser system. These have essentially zero maintenance, and no requirements for a gas supply or vacuum system. New systems in the 25 W range can be had for around $5,000 from companies like Parallax Technologies. This is certainly not cheap but may be in the ball park once all your costs and time are factored into the equation. However, note that in either case, there could still be considerable costs associated with the beam delivery system for your application. For example, focusing lenses to get power to that wood stock can easily run an additional several hundred dollars.
You may easily spend hundreds of hours in constructing a working CO2 laser - especially if it is your first home-built laser. Note that while this estimate may seem high, it doesn't only include the actual fabrication of the laser head itself (tube, mirror mounts, and frame) but the effort required to select, acquire, and set up the vacuum system, gas supply and metering system, power supply and possible added branch circuit(s) to handle the electrical load, cooling system, and support structure (stable table or frame). And, providing and preparing the physical space: The home-built CO2 laser is not likely to be in any way portable and the kitchen table does not make a good work area. Once everything is put together, all the leaks are plugged, the parts that got trashed in shipping are replaced, you will have to align the mirrors (best done with a helium-neon laser - another expensive if you don't own one already), start feeding gases, apply power, and hope everything holds together!
Even after you achieve 'first light' (or I suppose, more correctly, 'first IR'), you will then spend countless more hours in getting the laser to be a reliable system - and it is quite conceivable that this goal may forever be elusive. If your heart isn't in the laser construction aspects of this endeavor,you will get discouraged very quickly.
If you DO decide to build your own CO2 laser, don't shoot for the stars, at least not at first. Begin with a modest size tube of say, 2 feet in length, which should still be good for perhaps 20 or 30watts. There won't be any problems powering it with a 12 to 15 kV neon sign transformer and it will be small enough to easily fabricate - and store! Once you have gotten that operational, you will have solved all the tricky problems of vacuum, gas supply, mirror mounts, and cooling. It is easy to scale up something that works. However, starting with grandiose plans that fizzle will just lead to a box full of parts and equipment gathering dust in the attic.... :-(
Just to keep the expectations down, and also re-capping on the reason why we are building lasers in the first place.
For those who are building lasers for use as a tool, e.g., for metal or wood cutting, please be aware that you will be introducing a number of factors that will make it difficult for the final application.
Lasers for cutting applications should be producing a considerable amounts of power (around 100 Watts and up) to achieve a nice clean cut. At lower powers, it will take longer for the laser to cut the material, either if thin metal and or wood, and will cause burning and/or bad cuts. Another reason for having output powers in this range, is that at this wavelength, materials will behave differently(in terms of light behaviour) certain materials will reflect the IR energy, thus you are loosing energy through partial reflections.
Cutting lasers generally have to be very rouged, so to be resistant to fibrations that can cause mis-alignment of the optics.
Commercial CO2 lasers, are built so to be quite resistant to environmental changes. Also, many of the controls like vacuum, voltage/current, gas pressures/mixtures are electronically controlled.
For cutting applications, the laser beam must also be directed to the work piece, and this is done through an articulated arm - an optical waveguide. At the end of the arm, is the objective lens. These optics require to be enhanced for higher power IR beams, also it's not very easy at all, nor that trivial to build an articulated arm from scratch - much alignment involved.
Please be aware, that home built lasers are much more sensitive to vibrations, and are not of the 'plug-in and leave' variety. Home built lasers require much TLC, adjustments and continual tweeking, plus there is other things that have to be taken into consideration like: gas supply, mixture and gas pressure; power supply; mirror/tube adjustments and mounts; and thermal expansion and stability of the overall laser assembly.
Home-Built CO2 Laser Safety
There are three areas of safety considerations for the home-built CO2 laser (and other similar lasers, for that matter):- Laser output: The home-built CO2 laser producing high power infra-red radiation at a wavelength of 10.6 um. Almost any working CO2 laser - almost no matter how inefficient or misadjusted - will generate at least several WATTs of output power with scaled up designs similar to the SciAm laser capable of 100 W or more. This is enough to burn things like property, clothing, and flesh (including the structures you value at the front of your eyeballs).
Take precautions to avoid exposure to the direct or reflected beam. Since it is invisible, this means clearly labeling where it is and enclosing these in materials opaque to 10.6 um IR (these include glass and most plastics so it isn't that hard and doesn't obscure the action. Just because you can't see it, don't assume there is nothing there!
- Electrical: The power supplies can be lethal. Both AC and DC neon sign transformer based power supplies have enough voltage and current to stop a heart, Even if you aren't killed, the shock may startle you into doing something you might regret. Make sure you read and follow the Safety Guidelines for High Voltage and/or Line Powered Equipment. Insulate all connections and install barriers to prevent contact with the high voltage.
If you are using water cooling - either tap water or a closed loop system, make sure that water circulation paths are well insulated from the high voltage and that all fittings are securely grounded. Tap water is a fairly good conductor of electricity - think of it as a very soft wire. :) Unless you have a totally closed system filled with 100 percent distilled de-ionized water, there can be enough current flow to be lethal. Water and electricity do not mix!
- Hazardous substances: While the lasing gases (helium, nitrogen, and carbon dioxide) are not toxic, and are used in only small qunatities, there can always be leaks in the gas delivery system. CO2 in particular is heavier than air so it will displace air in an enclosed space which may result in various symptoms from nausea to asphyxiation. Make sure you have adequate ventilation. In addition, if you are generating any of these gases (rather than using separate tanks or pre-mix), acids or other caustic chemicals may be involved. Finally, the materials from which some of the optical components are made (like zinc selenide) may be biohazards if broken, ground, or even polished (more below). So, don't figure on making your own mirrors, windows, or lenses from this material. In addition, if you've inherited a commercial laser, it may use structural materials like beryllia for the bore, also a serious biohazard if broken or ground. See the section: Ion Laser Bore Temperature, Materials, and BeO Warning - written for ion lasers in particular but applies here as well).
Zinc selenide is an extremely toxic substance by ingestion and/or inhalation of dust, with a cumulative effect. This of course could be brought about if the optic were cracked or damaged in one's presence. This material liberates highly toxic hydrogen selenide in contact with gastric juices. Because of the material's reactivity with acids, it should NEVER be cleaned with even a weak acid, as these highly toxic H2Se vapors may be formed. Dermatitis may result from prolonged contact - don't play with your output couplers. :-) Although this material is practically insoluble in water, the use of gloves while handling the material is recommended. Gloves or finger cots should naturally be worn when handling any precision optic, as mentioned above. Particular care must be exercised when machining and creating dust or particles, not that I would think anyone will be machining their precious output coupler. :-) Symptoms of ingestion include garlic odor on breath. Ye best friend should tell thee. :-)
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Pressure Supply Laser Vacuum Vacuum Gas Supply => Regulator => Metering => Tube => Metering => Pump ==> Exhaust Valve Valve V1 o---/\/\-------/\/\------/\/\---o V2 R1 R2 R3
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D1 H o--------+ T1 T2 +--------+--|>|--+---o HV+ )|| ||=||( | | Variac )<--------------+ || ||( | D2 | 0-115V )|| )|| ||( +--|--|>|--+ 15A )|| Neon Sign )|| ||( | | )|| Transformer )|| || +--+ | | +--+ 12kV,100mA )|| ||( | | | D3 | )|| ||( | | +--|<|--+ N o-----+-------------------+ || ||( | | | ||=||( | | D4 | | | +--|--+-----|<|--+---o HV- | | | G o---------------------------+---+----+ _|_ ////
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