UV laser light is used in steriolithography (rapid prototyping), a process by which intricate prototype models are directly constructed from CAD (Computer Aided Design) data files, by polymerising a liquid plastic monomer. The UV light produces thermosetting of the liquid by inducing a cross linking reaction in the polymer. The process relies on a scanned laser beam to selectively harden successive thin layers of photopolymer, building each layer on top of the previous layer until a three dimensional part has been constructed.