The first laser was built in 1960 and laser marking systems came onto the market around 1977. They are, therefore, a well established technology and laser markers can operate continuously and in harsh environments. Laser markers have three main components:
- The lasing medium, which can be a liquid such as a dye but is more usually a gas such as carbon dioxide (CO2) or a solid such as Neodymium Yttrium Aluminium Garnet (Nd:YAG). Laser markers are either CO2 or YAG devices, which are described later. The lasing medium stores energy and then emits light (photons) to remove excess energy.
- The excitation mechanism, which applies energy to excite the particles of the lasing medium
- The optical resonator, which extracts the stored energy from the lasing medium in the form of a laser beam. It is often parallel mirrors at each end of the lasing medium, reflecting photons back and forth between them. One of the mirrors is only partially reflective ands so transmits some of the photons that hit it.
Photons pass through the lasing medium and cause its excited particles to release excess energy as additional photons. Some photons are transmitted by the partially reflective mirror to form the laser beam while the rest are reflected back to cause further energy release.
The beam marks the substrate by either removing material or changing its surface. In order to work correctly, it needs to be absorbed by the top layer of the substrate so it can modify the surface by ablation, annealing, engraving or chemical reaction (refer to the Technical Section for a description of these processes)
Both CO2 and YAG laser markers can use different technologies:
- Steered beam lasers where a lens focuses the laser beam to a small spot that then moves across the substrate to draw the characters or image. These systems use the laser beam efficiently, have low power requirements (10-20 W) and are generally entry-level devices.
- Mask lasers that focus a pulsed laser beam on a thin metal mask where the required image is etched. This allows high speed and detailed output although it is less flexible due to the mask, has high power requirements (2-12 MW) for short periods and the devices are often large.
- Dot matrix lasers that convert programmed code into a pattern of dots for versatile marking. Output is by either laser array (usually 5 or 7 lasers to create a dot matrix), rotating polygon that uses a multi-faceted mirror to create the dot positions or acousto-optic where the laser beam is deflected across a crystal dependent on sound wave frequency.