What is a CO2 laser and how does it work?
Thursday, December 16, 2021
To learn on the topic of CO2 lasers, look no further than this blog because at Gentec-EO we know a lot about this type of lasers given that our parent company Gentec inc. developed the first CO2 laser energy meter in the world in 1972. Since then, we never stopped striving to improve our product offering for this market.
They may be nearing their 60th birthday, but CO2 lasers are nowhere near retirement. In fact, their global market value is projected to increase by half a billion dollars by 2025.
All lasers require what’s known as a lasing medium. It’s in this lasing medium that the Light Amplification by Stimulated Emission of Radiation (LASER) happens.
Lasing mediums come in a few varieties: solid state, excimer, dye, semiconductor (or diode), and finally gas lasers, the family CO2 lasers are in.
You probably won’t be surprised to hear that CO2 is the active ingredient in making laser light in CO2 lasers. However, interestingly enough, CO2 lasers perform much better when the carbon dioxide is diluted to the point it only makes up about 20% of the total gas mixture. We’ll get into why soon.
A laser’s efficiency is often quantified by its “wall-plug efficiency”.
This measure of efficiency is calculated by dividing the amount of power in the laser beam by the electrical power required to operate the laser (including cooling systems and other losses).
The wall-plug efficiency of most CO2 lasers is generally somewhere between 10 and 20%, which is quite good, as far as gas lasers go. Especially when you account for the high beam quality CO2 lasers can offer.
But all the power and efficiency won’t be effective if you’re using the wrong wavelength. And this is where a CO2 laser’s effectiveness really shines.
Because CO2 is a triatomic molecule, it has many available energy levels. This means many different energy transitions can occur, which in turn means many different wavelengths can be produced in the mid-infrared portion of light’s spectrum. CO2 lasers’ main laser line is centered around 10.6 micrometers, but there are dozens more in the 9 to 11 micrometer range.
The atmosphere blocks many wavelengths, but has some small “windows” of wavelengths it lets through. One of these atmospheric windows coincides perfectly with a CO2 laser’s wavelength, making it a useful tool for observing the atmosphere. Which is a bit ironic when you think about it: CO2 is responsible for making the atmosphere more opaque (leading to the greenhouse effect), but this very same gas also powers one of the only lasers that is able to go right through the atmosphere.
In the medical field, the high absorption of mid-infrared wavelengths by water means that this laser interacts effectively with most biological tissues. As an added bonus, it has important hemostatic properties, which is just a fancy way of saying that if you cut blood vessels smaller than 0.5mm with a CO2 laser, there probably won’t be any bleeding. This has led them to be used in dentistry, the treatment of burn scars, skin resurfacing, and for surgeries.
And don’t even get me started talking about CO2 lasers are used in manufacturing. They can cut, weld, mark, engrave, harden, solder, 3D-print, and oh, they’ve recently found a niche in bleeding-edge computer chip manufacturing.
It was mentioned earlier that only about 20% of the gas mixture used for CO2 lasers is actually CO2. So what’s the other 80% and why don’t we just use 100% CO2?
Typically, about 20% is nitrogen, 1 or 2% is water vapor, hydrogen, oxygen or xenon, and the rest is helium.
For any laser to work, the first step is to give extra energy to the lasing medium. This is called excitation.
As it turns out, if you excite nitrogen, it can then transfer its energy surplus to neighboring CO2 molecules. And this method yields a much greater efficiency than what can be achieved by exciting the carbon dioxide directly.
Carbon dioxide has an array of different energy modes available to it. When laser light is emitted by the CO2 molecules, they can fall to lower modes of energy, without necessarily reaching the lowest mode of energy, which is required for optimal functioning of the laser.
Thankfully, when these low-energy CO2 molecules collide with helium, they transfer their leftover energy to the helium, thereby returning to their ground-state. This process is called relaxation.
CO2 can get degraded into carbon monoxide (CO) during laser operation. This is an undesirable side-effect, and having small amounts of water vapor or hydrogen can help trigger the conversion of CO back into CO2.
We hope this article helped you better understand what is a CO2 laser, how it works and how widespread this type of laser is. If you’ve got any questions you’d like answered, drop us a line. Our team of dedicated laser professionals will be happy to help.