All metals are reflective to CO2 laser beams, until a certain power density threshold value is reached. Aluminium is more reflective than C-Mn steel or stainless steel and has the potential to cause damage to the laser itself. Most laser cutting machines use a laser beam aligned normal to a flat sheet of material. This means that should the laser beam be reflected by the flat sheet it can be transmitted back through the beam delivery optics, and into the laser itself, potentially causing significant damage. This reflection does not come entirely from the sheet surface, but is caused by the formation of a molten pool which can be highly reflective. For this reason, simply spraying the sheet surface with a non-reflective coating will not completely eliminate the problem. As a general rule the addition of alloying elements reduces the reflectivity of aluminium to the laser, so pure aluminium is harder to process than a more traditional 5000 series alloy.
With good, consistent cutting parameters the likelihood of a reflection can be reduced to almost zero, depending on the materials used. However it is still necessary to be able to prevent damage to the laser while developing the conditions or if something goes wrong with the equipment. The 'aluminium cutting system' which most modern equipment uses is actually a way of protecting the laser rather than an innovative technique for cutting. This system usually takes the form of a back reflection system which can detect if too much laser radiation is being reflected back through the optics. This will often automatically stop the laser, before any major damage is caused. Without this system there are risks with processing aluminium as there is no way of detecting if potentially hazardous reflections are occurring.

Note: Always check with the laser supplier that the system is designed for processing aluminium before attempting to cut it. Some other materials, for example brass, may also require the back reflection protection system so it is also advisable to check with the supplier before processing any new material.