CO2 Lasers
CO2 lasers pass an electric current through a tube filled with a gas mixture, producing a beam of light. There is a mirror at each end of the tube. One mirror reflects completely, while the other partially reflects, letting some of the light through. The gas mixture is usually carbon dioxide, nitrogen, hydrogen, and helium. CO2 lasers produce invisible light, in the far infrared range of the spectrum.
The highest-power CO2 lasers for industrial machines can reach several kilowatts, but these lasers are definitely the exception. Typical processing CO2 lasers have a power of 25 to 100 watts and a wavelength of 10.6 microns.
This type of laser is most commonly used to process wood or paper (and its derivatives), polymethyl methacrylate, and other acrylic plastics. It is also suitable for processing leather, fabric, wallpaper, and similar products. It has also been applied to the processing of foods such as cheese, chestnuts, and various plants.
CO2 lasers are generally best suited for non-metallic materials, although they can process some metals. It can usually cut thin aluminum and other non-ferrous metals. One can enhance the power of a CO2 beam by increasing the oxygen content, but this can be dangerous for an inexperienced person or a machine that is not suited for such enhancements.
Fiber Lasers
This type of machine belongs to the solid-state laser group and uses a seed laser. They amplify the beam using specially designed glass optical fibers that draw their energy from a pump diode. Their general wavelength is 1.064 microns, which produces an extremely small focal diameter. They are also generally the most expensive of the various laser cutting equipment.
Fiber lasers are generally maintenance-free and have a lifespan of at least 25,000 laser hours. Therefore, fiber lasers have a much longer lifespan than the other two lasers and can produce a powerful and stable beam. They can reach intensities 100 times higher than CO2 lasers at the same average power. Fiber lasers can be continuous beams, quasi-continuous beams, or offer pulsed settings, providing different capabilities. A subtype of fiber laser systems is the MOPA, where the pulse duration is adjustable. This makes MOPA lasers one of the most flexible lasers and can be used in a wide variety of applications.
Fiber lasers are best suited for metal marking via annealing, metal engraving, and thermoplastic marking. They work well with metals, alloys, and non-metals, even glass, wood, and plastics. Fiber laser cutting machines are extremely versatile and can process a large number of different materials, depending on the power. When processing thin materials, fiber lasers are the ideal solution. However, for materials over 20 mm, the situation is less ideal, but a more expensive fiber laser machine with a power of over 6 kW will also suffice.
Nd:YAG/Nd:YVO Lasers
Crystal laser cutting processes can use nd:YAG (neodymium-doped yttrium aluminum garnet), but more commonly use nd:YVO (neodymium-doped yttrium vanadate, YVO4) crystals. These devices have extremely high cutting powers. The downside to these machines is that they can be expensive, not only because of their initial price, but also because their life expectancy is 8,000 to 15,000 hours (Nd:YVO4 is generally lower), and the pump diodes can be very expensive.
These lasers have a wavelength of 1.064 microns and are used in a variety of applications from medical and dental to military and manufacturing. Comparing the two lasers, Nd:YVO has higher pump absorption and gain, wider bandwidth, wider pump wavelength range, shorter upper level lifetime, higher refractive index, and lower thermal conductivity. In continuous operation, Nd:YVO has similar overall performance levels to Nd:YAG at medium to high powers. However, Nd:YVO does not allow pulse energies to be as high as Nd:YAG, and the laser has a shorter lifespan.
They can be used on both metals (coated and uncoated) and non-metals, including plastics. In some cases, it can even process some ceramics. Nd:YVO4 crystals have been used in combination with high NLO coefficient crystals (LBO, BBO or KTP) to shift the output from the near infrared to the green, blue and even the ultraviolet, giving it a host of different functionalities.
Due to their similar size, the yttrium, gadolinium or lutetium ions can be replaced with laser-active rare earth ions without greatly affecting the lattice structure required to produce the beam. This allows the high thermal conductivity of the doped material to be maintained.