Three-dimensional direct laser writing inspired by stimulated-emission-depletion microscopy

Three-dimensional direct laser writing has become a well established, versatile, widespread, and even readily commercially available "workhorse" of nano- and micro-technology. However, its lateral and axial spatial resolution is inherently governed by Abbe's diffraction limitation - analogous to optical microscopy. In microscopy, stimulated-emission-depletion approaches have lately circumvented Abbe's barrier and lateral resolutions down to 5.6 nm using visible light have been achieved. In this paper, after very briefly reviewing our previous efforts with respect to translating this success in optical microscopy to optical lithography, we present our latest results regarding resolution improvement in the lateral as well as in the much more relevant axial direction. The structures presented in this paper set a new resolution-benchmark for next-generation direct-laser-writing optical lithography. In particular, we break the lateral and the axial Abbe criterion for the first time.