Principles of voxel refinement in optical direct write lithography

Optical direct write lithography (ODWL) has the capacity for generating three dimensional arbitrary patterns. Here we examine principles for voxel refinement and relate several techniques for achieving nanoscale resolution. The influence of optics, gelation, and polymerization scaling behavior are expounded, demonstrating the necessity for adopting a multidisciplinary mindset to control both voxel dimensions and minimize out-of-focus reactions. Aspects of two-photon ODWL are reviewed and recent multi-beam ODWL approaches that draw inspiration from STED microscopy are examined.