The term 'YAG' is commonly used to describe a laser system that is used for metal and plastics marking applications. There are many different types of YAG laser. The wavelength of a YAG laser for most marking/engraving applications is typically:
The beam of this type of laser is created by shining a light (the source) through an active medium. Both the source and the active medium can be a variety of different elements.
There are two main types of laser source used for YAG laser marking systems:
Both are used to pump the laser medium giving rise to the terms 'lamp-pumped' laser and 'diode-pumped' laser.
When compared to modern alternatives lamp-pumped YAG laser technology is old, inefficient, unstable and high in terms of maintenance and running costs. Such machines are large in footprint, consume large amounts of energy (often 3-phase) and generate a lot of heat as a by-product. As a consequence, large water-cooling chillers are required for this type of machine. The lamp is a consumable item that in some cases requires replacement as often as every 400 hours of use. The only real advantage of a lamp-pumped laser is its high power output, which is not usually necessary for most marking applications. Therefore, lamp-pumped YAG lasers are rarely used these days as marking machines.
The alternative to using a lamp as the source to pump the active medium is to use diodes. Most systems use several diodes arranged as bars, stacks or in an array. The benefits of this type of source are significantly increased efficiency, stability and output quality. System footprint and energy consumption are lower by comparison to a lamp-pumped system. Power input for a diode pumped machine is single phase. Heat output from this type of machine requires the use of a closed loop water chiller but this is normally quite small in size. Running costs are relatively low. The diode array is considered a wear item but often has a working life of several thousand hours, so it's not really a consumable in the same sense that a lamp would be.
YAG is an acronym for Yttrium Aluminium Garnet. These three elements are used to create a man made crystal. This crystal, or rod as it is otherwise known is doped with a rare-earth substance, for example, Neodymium (Nd:YAG) and placed within a chamber to work as the active laser medium. Nd:YAG is the most commonly used rod within laser marking systems as it is reasonable in cost, high in output quality and it provides for relatively high power output. Another form of laser rod is Yttrium OrthoVanadate (Nd:YVO4) - commonly called a vanadate laser. Vanadate lasers are useful for plastics marking applications that require very low power but they are not suitable for annealing or ablation of metals.
The laser source illuminates the rod to cause the inversion, which creates the laser beam.
Major recent technological breakthroughs have enabled an optical fibre to be used as the laser medium instead of a rod. The benefits are even greater than diode technology providing for a much higher quality, more stable beam with hardly any heat being generated as a by-product of the process. Therefore, no chiller is required; simple air-cooling is sufficient.
Fibre lasers, as they are collectively known, are very small in footprint and some models are even portable. Energy consumption is exceptionally low and such machines will operate from a typical domestic (13a) supply. beam quality and effective power output are excellent. System maintenance is nigh on non-existent. Such technology does not have any consumable parts. The source of a Fibre Laser is expected to last for tens of thousands of hours. So it's no surprise that Fibre Lasers are fast becoming the default YAG technology for most marking applications.