C02 Laser Design
The CO2 laser, once an industry work-horse, has been eclipsed by newer laser designs that are more narrowly focused toward specific uses. However, because of its unique design and function, the CO2 laser is still an irreplaceable tool for many industrial applications that cannot be matched by other technologies. Optical systems can focus the light energy into small spot sizes useful in metal cutting, welding, cladding, and heat-treating applications. Here’s why it works so well in so many heat treating, welding, and other hard-surfacing applications.
Essential components
The CO2 laser is comprised of two basic parts. The first part includes the components that generate the laser energy, and the second part is the beam delivery system that translates the laser energy into a light beam that can be used. The energy-generating part of a CO2 laser consists of a lasing medium, an optical resonator to contain the lasing medium, and an excitation source for the lasing medium.
A lasing medium is the original source of the energy for the laser. The lasing medium in a CO2 laser is a mixture of carbon dioxide, helium, and nitrogen gas.
In an axial-flow type of CO2 laser, the gas is contained in a long double walled glass tube. This glass tube is the optical resonator and has reflecting mirrors mounted at each of its ends. High electrical voltage is the excitation source applied to the gas in the resonator to excite the CO2 molecules to a higher energy level.
Making light
As the gas mixture is electrically charged, the excited molecules try to find a more stable energy level. In the process, they emit energy in the form of photons. This is similar to a controlled chain reaction, as each emitted photon stimulates the emission of more photons from other excited molecules. Every photon emitted by the excited CO2 molecules has exactly the same wavelength.
As the energy beam develops from the excited photons, the mirrors at the ends of the optical resonator catch the photons traveling parallel to the axis of the resonator and reflect them back down the resonator. This process further amplifies the energy content of the beam by stimulating the emission of even more photons. The optical resonator makes all the energy flow in one direction, since all reflected photons are traveling in a direction parallel to the resonator’s axis.
The energy within the laser is of no value until it can be directed out of the unit and onto a work surface. An output coupler is used to get the energy out of the optical resonator so it can be used for some work application. To form the output coupler for a CO2 laser, one of the mirrors on the end of the resonator tube is made only partially reflective.
This partially reflective mirror allows about 50 percent of the laser beam to exit the optical resonator, and that portion is used for the laser’s intended application. The remaining 50 percent of the beam continues to stimulate photon emission in the excited CO2 molecules inside the resonator. The output coupler focuses the exiting beam to produce high energy densities in a small area.
Making heat
The laser beam is simply an energy source until it contacts the surface of a work piece. To make the light beam useful, lasers have optical systems that use reflectors and lenses to direct the beam from the optical coupler to the work piece.
Because a CO2 laser beam retains most of its power over long distances, the optical systems can direct the beam to a workstation located quite a large distance from the laser. The beam can even be split and shared among more than one workstation, as it is in BMR Group’s facility in Wolf Lake, Indiana.
BMR Group has used CO2 laser technology for two decades, helping customers conquer or alleviate wear problems caused by everyday operation in difficult production environments. If you’d like to learn how this same technology might help you improve your productivity and your bottom line, call BMR Group at 260-635-2195 or drop us an email explaining what you want to accomplish.
