3D laser printing below the diffraction limit using two-step absorption and depletion

The recent implementation of two-step photoinitiators (Nat. Photon. 15, 932-938 (2021)) for three-dimensional nanoscale direct laser writing has enabled printing with low cost, low power laser diodes while preserving the nonlinear relationship between printing and incident light intensity found in two-photon absorption. Thus far, this method has been able to achieve very high printing resolutions at the diffraction-limit. In order to further improve this resolution, we implement a photoinhibition scheme inspired by stimulated emission depletion (STED). Similar schemes have previously been used in two-photon absorption-based printing and have successfully demonstrated printing resolutions beyond the diffraction limit. Thus, in this work we use a novel, depletable, two-step photoinitiator to combine two-step printing with STED-inspired techniques and achieve sub-diffraction limited printing resolution in a compact, stable optical setup.