The main differentiating factor between laser systems is their gain medium. In short, a laser's gain medium is the substance which, when supplied with energy, generates a laser's beam. Click here to learn more about how lasers work.
Carbon dioxide (CO2), fibre, and vanadate lasers — which are named after their respective gain mediums — are among the most common laser types available on the market. Each offers distinct advantages with regards to workpiece processing.
A carbon dioxide (CO2) laser beam is derived from a carbon dioxide gas mixture contained inside a resonator. Laser light is created when the gas mixture is stimulated by an electrical current. CO2 laser beams are not visible to the human eye, as their 10.6-micrometre wavelength is situated in the far-infrared range on the electromagnetic spectrum.
A C02 laser is well suited to processing the following materials, as they are able to absorb its beam:
Although uncoated metals cannot be engraved using a CO2 laser, it is possible to mark some coated metals. For example, when anodised aluminum is processed with a CO2 laser, etchings that are white in appearance remain as the coating is burned off. Similarly, markings can be made on uncoated metals treated with specially formulated compounds (the laser beam's heat bonds the solution to the workpiece, leaving black markings).
A fibre laser's gain medium is an optical fibre enhanced with rare-earth element traces. One or more low-energy diodes (also known as seed lasers) emit light beams, which are amplified and channeled by the optical fibre to generate a laser beam.
With a wavelength of 1.064 micrometres, fibre lasers beams are in the near-infrared range on the electromagnetic spectrum. This wavelength is relatively long, which enables fibre lasers to vaporize metal. In other words, metal and coated metal surfaces can be engraved using a fibre laser.
MOPA (master oscillator power amplifier) laser is a distinct type of fibre laser, which has predetermined adjustable pulse durations (between 4 and 200 ns). This unique characteristic offers the user a high degree of flexibility when processing metal workpieces. For example, anodised aluminum can be marked in different shades of black and uncoated steel can be annealed in different colours. In addition, MOPA lasers are capable of creating high-contrast markings on some plastics.
A vanadate laser's gain medium is a crystal, which is typically supplied with energy by diodes or lamps. The most common vanadate laser types are Nd:YAG (neodymium-doped yttrium aluminum garnet) and Nd:YVO (neodymium-doped yttrium orthovanadate), named after their doping element (neodymium) and respective crystal components.
Vanadate lasers (or crystal lasers, as they are sometimes known) have a standard wavelength identical to that of fibre lasers (1.064 micrometres), and are thus also suited for marking metals. Unlike fibre lasers, however, vanadate lasers often use relatively expensive pump diodes. These components must be replaced after approximately 8,000 – 15,000 laser operation hours. Nd:YAG and Nd:YVO crystals also have a shorter service life than a fibre laser's optical fibre.
Crystal lasers are capable of processing the following materials:
- Coated metals
- Ceramics (to some extent)