Multiphoton photochemical process and articles preparable thereby

A process comprising:

• a) providing a photoreactive composition, the photoreactive composition comprising at least one reactive specie and a photochemically-effective amount of a multiphoton photoinitiator system, wherein the multiphoton photoinitiator system comprises a multiphoton absorber having a two-photon absorption cross section greater than or equal to the maximum two-photon absorption cross-section of fluorescein;
• b) exposing at least a portion of the photoreactive composition to light of appropriate wavelength and intensity such that simultaneous absorption of at least two photons by the photoreactive composition occurs, thereby causing at least partial reaction of at least one reactive specie and causing a portion of the photoreactive composition to become more, or less, soluble in at least one solvent than the photoreactive composition before exposure to the light, wherein the light passes through an optical system having a final optical element prior to reaching the photoreactive composition, and wherein the final optical element has a numeric aperture in a range of from 0.65 to 1.25, inclusive;
• and
• c) developing the exposed photoreactive composition.