Deep super-resolution direct laser writing using Gaussian and Bessel Beam

Direct laser writing (DLW) has been an emerging technique for creating complex nanostructures due to its high flexibility, high precision, and digital-control capabilities. However, the Abbe diffraction limit of laser writing system often restricts its resolution. Combining stimulated emission depletion (STED) with DLW offers promising prospects for improvement. Yet conventional STED systems using Laguerre-Gauss depletion beams suffer from severe spherical aberration due to the index mismatching between samples and optical system, leading to resolution degradation at deeper sample depths. This work proposes a Gauss-Bessel STED (GB-STED) system employing a first-order Bessel beam for depletion. Due to its self-healing properties and minimal spherical aberration susceptibility, the GB-STED system achieves deep super-resolution DLW with linewidths nearly identical to the surface. Debye vector diffraction integral simulations has been performed to compare the optical field distributions and linewidths of STED and GB-STED systems. Experimentally, a two-photon super-resolution DLW system based on the Bessel beam demonstrated constant resolution throughout the sample depth. These results showcase the superior super-resolution DLW capability of the GBSTED system at depth, opening new avenues for high-resolution laser nanofabrication.