Optical projection lithography at half the Rayleigh resolution limit by two-photon exposure

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Abstract
Photographic media can be exposed by two-photon absorp- tion, rather than the more usual one-photon absorption. This leads to the question of whether the simultaneous absorption of a pair of photons could be accompanied by a twofold spatial-resolution enhancement. We find that ordinary two-photon absorption merely enhances the photo- graphic contrast, or gamma. While this improves the spatial resolution somewhat, it does so at the expense of requiring tighter control over the incident light intensity. Instead, we introduce a new type of exposure arrangement employing a multiplicity of two-photon excitation frequen- cies, which interfere with one another to produce a stationary image that exhibits a true doubling of the spatial resolution. © 1999 Society of Photo- Optical Instrumentation Engineers. (S0091-3286(99)00402-X) Subject terms: photolithography; two-photon absorption.