Laser marking is like burning leaves with a magnifying glass...
In order to burn a leaf with a magnifying glass one would collect the rays of the sun through a simple lens and place the lens over the leaf at the focal point of the lens. The sunlight collected by the lens then focuses on the leaf and concentrates sunlight on a small spot on the leaf and bingo....the resulting heat causes the leaf to smoke and eventually catch fire.
Laser marking systems employ exactly the same principals. Instead of sunlight being passed through a simple lens, laser light is passed through a more complex lens; an f theta lens. While sunlight consists of many colors or wavelengths, laser light has the property of being monochromatic. Laser light is all the same color or wavelength. The wavelength depends on the type of laser. Different materials absorb different wavelengths of light. If the material placed under the laser happens to absorb the wavelength of that laser then there is a good match.
For laser marking applications the laser beam is focused onto the surface of the material to be marked with an f theta lens. An f theta lens has the property of being able to maintain its focus throughout a plane, rather than just being in focus at one spot. The laser beam is steered through the f theta lens by a pair of computer controlled mirrors. The laser beam can be focused on the material anywhere within the plane defined by the f theta lens and if there is a good match between laser wavelength and material the result will be a mark left on the material. That mark can be in the form of graphical images, text, machine readable codes such as barcodes, UID codes of 2D codes or any other imaginabletype of mark.
Different laser types are suitable for different materials. If one wanted to mark wood, for example, the optimum wavelength of light for that material is that produced by a CO2 laser. If one wanted to mark metals, the optimum wavelength would be that produced by a YAG or Fiber laser. The material to be marked dictates the type of laser that is needed. There is no such thing as a laser that is well suited for all materials.