Stereolithography is a generic process, also known as vat photopolymerization. Its variants are microstereolithography, digital light processing, large area maskless photopolymerization, etc. In this process, photosensitive polymers are irradiated with light (UV or other lasers), which causes photons to interact with electrons and polymer molecules. The interaction creates either free radicals by breaking bonds or ions (cations) by removing electrons. The free radicals or cations bond with other polymer molecules, which enables them to bond again with other polymers, resulting in an increase in chain length, viscosity, gelling, and molecular weight. Polymer chain formation is known as polymerization. Since a low-energy photon is sufficient to trigger polymerization, a laser power of a few mW is sufficient, which is in contrast to the high laser power of hundreds of watts used in metal powder-based AM, as high-energy photons are required to break metallic bonds and melt them.