I was getting some laser engraving done by the nice people over at Trilogy Lasercraft, a nearby company. They showed me some of their machines in operation, and they’re great fun to watch. This was for another customer:
They cut and engrave lots of different materials, but paper and card form quite a big part of their business. The light that you see is not the laser, which is infrared and invisible. It’s the flaring of the paper particles that are burned off.