STED ‐Inspired Approaches to Resolution Enhancement

This chapter focuses on two-color approaches to resolution enhancement in two-photon polymerization. The optical technique has inspired most of the approaches to two-color lithography, stimulated emission depletion (STED) fluorescence microscopy. Traditional fluorescence microscopy faces some of the same challenges, as in photolithography. The Abbe criterion dictates the minimum distance between resolvable features in imaging. However, in fluorescence microscopy, photodamage limits the shortest wavelength of radiation that can be employed, particularly in the case of live-cell imaging. Super-resolved techniques for optical microscopy were enabled by the realization that if one can use photochemical or photophysical means to prevent nearby fluorophores from being excited simultaneously, then there is no reason why the resolution of fluorescence microscopy cannot be far better than what is predicted by the Abbe criterion. The two-color techniques may lead to tabletop tools that can be used to perform 3D lithography with a resolution that rivals that of electron-beam lithography.