In order to understand what makes a laser suitable for cutting, one must distinguish its unique
features in comparison to ordinary light.
Conventional light produces waves, which radiate out in all directions to fill up and illuminate a
wide area. The energy intensity rapidly decreases as waves moves away from the source,
just as the sun's intensity is diminished when it finally reaches the earth.
The laser on the other hand provides a stream of collimated, coherent light waves which give
it exceptional intensity and direction ability. Lacking the dispersion of conventional light, a
laser can be easily projected as a beam over relatively long distances while maintaining
nearly all of its useful power output.
The use of lasers for cutting can be thought of in the same way as that of focusing sunlight
with a magnifying glass to produce a concentrated source of heat energy. While this method
only results in a few burned holes in paper, it gives us an illustration that light is indeed a
source of energy with potential material processing capabilities.
A laser can be used for cutting by exposing material to the intense heat energy developed by
its beam. If that heat input to the material is greater than that material's ability to reflect,
conduct, or disperse the added energy, it will cause a sudden rise in temperature of the
material at that point. If the temperature rise is substantial enough, the input heat is capable
of initialising a hole by vaporizing the material. The linear movement of this intense heat
energy with respect to the material provides cutting action.
In most cases the "raw" (unfocused) beam of even high power (multi-kilowatt) industrial lasers
has inadequate energy to do much more than slowly heat a surface. Therefore, the beam is
directed through a focusing lens. This allows the energy to be concentrated into a spot of less
than 0.25 mm thus producing power densities of over a million watts per centimeter squared,
capable of vaporizing many materials.
While intense heat is capable of vaporising material, the control of that heat is essential in
determining quality. The key performance features of a laser are those beam characteristics
that affect the resultant power density as it is directed onto the workpiece.