A laser engraving machine is a high-tech collection of electronic and mechanical components. The three critical pieces are the laser system, the controller that dictates its motion, and the surface that the laser ablates material from. The nature of each component determines the potential applications of the engraving apparatus as a whole, so it is important to understand the options available on the market.
Laser: A pulsed or continuous wave laser system can be used as the energy source for an engraving setup. Continuous wave lasers are cheaper and more rugged, but must be run at significantly higher average powers to achieve the same results as a pulsed laser. The laser beam is collimated and then passed through a focusing lens to reduce fluctuations in the laser beam profile. The laser is focused down into a very small bright spot, approximately one millimeter or less in diameter. The small focal spot creates a very high peak power, and it also improves the resolution of the patterning. As the laser delivers focused energy to the engraving surface, much of that energy is converted to heat, and can cause excess heating of the apparatus. This is when pulsed lasers, which deliver tiny packets of energy one after another, can reduce unnecessary heating of the engraving surface.
Controller: The controller is a computer-controlled series of motors that move either the laser or engraving surface in the x and y directions. The tracking vectors can be pre-programmed to create patterns or designs on the surface, with incredible repeatability. For cylindrical surfaces, sometimes the laser itself must be pulsed on and off to achieve the desired ablation pattern. Alternatively, if neither the laser nor surface stability allows for continual motion, a pair of galvanometer mirrors can be tilted and rotated to direct the laser beam accordingly.
A few parameters that the controller system has to work with are the laser beam trace, the rastering speed, and the duty cycle of the laser. The beam trace is generally a long single pass over the desired etching, ensuring that the etching depth is consistent across the pattern. The speed of the laser can be adjusted to reduce unwanted melting, and the duty cycle can be lengthened or shortened to match the energy delivered by the laser with the strength of the engraving surface material.
Engraving Surface: The focal plane of the laser is aligned to just barely touch the engraving surface. Without the proper depth positioning, the laser power will not be sufficient to engrave cleanly, and burn spots or melted edges can be observed. The energy from the photons in the laser heat up the surface and vaporize bits of material until the clean lines of the desired engraving are achieved. Materials that are commonly subjected to laser engraving include glass, plastic, and metal. Even very delicate surfaces are suitable for laser engraving because the controller programs the engraving pattern and no bulky resistive mask is needed to guide the laser beam. These masks can damage the surfaces they are supposed to shield from ablation, and often leave residues behind that require cleaning with harsh chemicals.