Laser Cutting Services
All laser machines at Cirrus Laser are CO2 gas lasers with a wavelength of 10.6 microns (far infrared), other types of lasers used in Industry, Medical and Scientific applications are solid state or diode types operating at different (shorter) wavelengths. Gas lasers generate the laser beam inside a resonator; normally made from glass, however, ‘slab’ lasers have machined aluminium resonators. Inside the resonator there is a partial vacuum of about 120 mBars and filled with Helium, Nitrogen and CO2 gases in approximate proportions of 80% / 18% / 2% respectively. The different wavelengths of lasers determines the type of materials that can be cut and typically CO2 gas lasers are good at cutting hard materials such as metals.
Our two Trumpf lasers use a RF generator to excite the CO2 gas molecules within the resonator, some lasers use a DC High Voltage power supply for excitation, which produces the single wavelength, polarized beam, of stimulated photons. The name ‘Laser’ is the acronym of Light Amplification by Stimulated Emission of Radiation, and the RF or DC high voltage is used to impart energy to the CO2 gas molecules, which move to a higher energy state and release a photon when they return to their normal state. Within the resonator there is a partial mirror, which releases about 35% of the photons for the cutting process and the other 65% of photons return inside the resonator. These returning photons collide with CO2 gas molecules in the resonator and form the “Stimulated Emission” by imparting energy to the CO2 molecules which release more photons and (importantly) are in phase and in the same direction as the original photons.
The raw laser beam has a diameter of about 25mm and is totally enclosed within the machine for safety. However, the raw beam will not accurately cut materials until it has been focused through a lens made from Zinc Selenide (ZnSe), the beam diameter at the focal point is about 0.15 to 0.4mm diameter depending on the focal length of the lens. Typically CO2 gas lasers use lenses of 3.75ins, 5ins, 7.5ins or 9ins focal length, with the ‘spot size’ increasing with larger focal length. The process is very similar to using a magnifying glass to concentrate the Sun’s energy and burn combustible matter, just like children burning leaves or grass on a hot summers day. However, unlike the Sun’s energy, which has the complete spectrum of light wavelengths, lasers have a single (monochromatic) wavelength, which enhances the beam focusing and material absorption characteristics.
The focused laser beam is used to vapourise the material to be cut, however, an additional cutting gas, or assist gas, is needed to blow or remove the molten material through the thickness of the metal being cut. It is exactly similar in principle to oxy / acetylene or oxy / propane cutting, where a fuel gas and oxygen are used to heat the metal until molten and then an additional nozzle blows oxygen through the material thickness to remove the molten metal. But although the principles are similar between oxy / acetylene and laser cutting, the control and fine detail obtainable from the laser process is far superior to most other heat cutting processes.