Entry chosen by Grant England
Multiphoton lithography involves any process which requires more than one photon for photochemical activation. Since the reaction (usually photopolymerization requires more than one photon to be present in the same location in order for it to occur, the probability of this occurring is only large enough near the focal point of a scanning laser beam which is used to three-dimensionally write the material.
Methods for large area patterning using multiphoton lithography have been developed by using conformal phase masks , but these are currently limited to periodic structures such as 3D Photonic crystals.
Wikipedia stub: