Laser cutters are some of the most useful and versatile tools available in a workshop. The principle of operation is similar to that of other computer-controlled machine tools, except that laser cutters use an intense light beam instead of a blade or milling cutter.
By directing a powerful laser beam onto the work through a focusing lens, a laser can engrave or cut. The laser can even switch between engraving and cutting in the course of a single machining pass, changing from a high power cutting device to a sophisticated printer that etches an image onto the part after cutting. Follow this link to find a variety CO2 laser machines for sale.
A laser works by exciting a lasing medium within a chamber that has mirrored ends. The resulting light is amplified as it bounces between the mirrors. One of the mirrors allows a small fraction of this light to escape, and the resulting beam can be focused to a microscopic spot so intense that it can cut through or write on many different materials.
The CO2 laser that is used for most machining are gas lasers. Electricity or RF radiation is passed through the CO2 gas to excite it and produce light. The CO2 laser tube has a fully reflective mirror on one end, and a partially transparent mirror on the other. The gas inside is not pure CO2, but rather a mix of carbon dioxide, hydrogen, nitrogen, and helium. Despite the laser being called a “CO2″ laser, the nitrogen is still critical to its operation.
How a CO2 Laser Beam Works
When electricity or high power radio frequency waves are passed through the gas, this excites the nitrogen molecules and causes them to gain energy. Nitrogen molecules are so called homonuclear molecules, which means they’re unable to give off this energy as light. Instead, they have to pass the energy on to molecules around them.
Eventually, the excited nitrogen molecules excite the CO2 molecules next to them. Once there are more excited molecules than non-excited ones, the state is called population inversion.
Population inversion is key to laser operation. The laser tube is fundamentally an amplifier, not a light source. When a CO2 molecule is in the excited state, a photon of the right wavelength (10.64 micrometers) will cause the excited molecule to emit another photon at precisely the moment the original photon passes by. This makes for two photons in perfect lockstep, “coherent” photons.
The reason population inversion is necessary is simple. If a CO2 molecule is not excited, and a photon with the right CO2 wavelength passes by, the CO2 molecule will gobble up the photon and use its energy to excite itself. If there are more non-excited CO2 molecules than there are excited ones, more photons will get gobbled up than get emitted. This would result in a net reduction of light, rather than a net amplification.
Once a population inversion exists, all it takes is one photon to set off a chain reaction. Eventually some photons start being produced spontaneously. One of these eventually happens to be going in the right direction to bounce between the mirrors. As this photon bounces back and forth between the mirrors, it triggers the emission of other photons along with it, all moving in lock step. That’s a laser beam.
The power output of a laser depends on how much energy can be fed in to keep this reaction going, as well as how many molecules are available to do the amplifying. Surprisingly, in CO2 lasers it’s also very important to make sure the CO2 atoms stay cool, otherwise the population inversion is harder to achieve and the output power goes down.
Since the only light that bounces back and forth between the mirrors is precisely parallel, lasers produce a beam with very parallel sides, a so-called collimated beam. A collimated beam can be focused to an extremely tiny spot. Combined with the high power output, this makes for an extremely high power density at the material. The higher the power density, the higher the temperature, and the temperature at the laser spot is hot enough to vaporize glass and steel.
If the laser manufacturer wants even more power out of a laser tube, they can use something called a Q-Switch. This device sits in front of one of the laser mirrors, and prevents the laser action from happening until the population inversion has reached a really thorough point, and almost all the atoms are excited. Only then does the Q-Switch allow the laser to fire. The result is a short but enormously powerful pulse of light, as all the atoms let loose in concert.
Applied to machining, the main benefit of a CO2 laser cutter is its precision. You can use it for laser wood or acrylic cutting to make very detailed patterns. Depending on the lens it may be possible to create a spot as small as 0.002 inches. Since the laser never comes into contact with the material, there’s no risk of distorting the work (except by excessive local heating).
How powerful a laser will I need to work a given material?
The answer to this very common question depends on the material type and thickness, but also on the speed at which you want to process it. Some materials cut and engrave easily with even a weak laser, while other materials require a stronger laser or multiple passes. Consult your laser manufacturer’s applications department for advice as to what their firm’s different models can do given your application.
Lasers are meant to be used as components within a larger system of optics and mechanical positioning devices. 40 to 100W laser cutters are commonly used for machining organic materials, specifically:
- 3D Prototyping
Entry level laser cutter machine prices start in the 8000-10,000 USD range, though some Chinese vendors offer laser cutters for sale at lower prices and correspondingly lower quality. CO2 laser cutter DIY options are also available for highly skilled and dedicated hobbyists, but the complexity and safety issues involved in working with lasers means that these are very much not beginners’ projects.
CO2 lasers used for industrial materials processing like cutting or welding metals are far more powerful and carry price tags correspondingly larger. Standing in competition with much more efficient Nd:YAG lasers, industrial CO2 lasers are still used because — despite their comparative inefficiency — they allow for continuous beams (necessary for “keyhole” mode welding) and smaller spot sizes than Nd:YAG systems would.
The excellent properties of CO2 lasers when used for organic materials processing means they’ve seen considerable adoption in the medical field, where they’re used for laser surgery. CO2 lasers’ efficiency has also made them a good choice for certain types of range finding.