Patent ID: 7166409

Claim:
A method of increasing the efficiency of a multiphoton absorption exposure process, the method comprising: providing a photoreactive composition; providing a source of infrared or visible light sufficient for simultaneous absorption of at least two photons by the photoreactive composition; exposing the photoreactive composition to at least light of a first transit of light from the light source to effect simultaneous absorption of at least two photons by the photoreactive composition; directing at least a portion of the light from the first transit of light back into the photoreactive composition using at least one optical element and focusing the light sufficiently to effect simultaneous absorption of at least two photons by the photoreactive composition; and wherein a plurality of photons not absorbed in the first transit are used to expose the photoreactive composition in a subsequent transit; wherein the efficiency of the multiphoton absorption exposure process is increased relative to the same process that uses only one transit of light; and further wherein directing at least a portion of the first transit of the light back into the photoreactive composition comprises directing at least a portion of the first transit of the light back into the photoreactive composition at a location different from that exposed to the first transit of light.