Two-photon direct laser writing (DLW) lithography is a powerful tool to fabricate 3D structures with feature sizes of ~100 nm. This technique is based on the quadratic dependence of the absorption of near-infrared (NIR) light (two-photon absorption, 2PA) by molecules called photoinitiators which trigger the photopolymerization of curable resins. With the aim of downsizing the structures to the nanometer resolution, a requirement of the microelectronics industry, a new strategy has been added to the DLW lithography, the two-beam approach (excitation and inhibition beams) based on the reversible saturable optical fluorescence transition (RESOLFT) concept. This approach is borrowed from the field of super-resolution fluorescence microscopy and consists in the reversible depletion of some intermediate excited state of the photoinitiators only at some specific areas of the point spread function (PSF) of the excitation beam. The objective of this project is to further develop the two-beam DLW lithography to make it more competitive compared to other advanced nanofabrication techniques. The project is conducted to overcome the limitations of the two-beam DLW lithography: 1) the large feature size, the state-of-the-art has recently been pushed to 9 nm line width from a previous value of 55 nm, and 2) the large spatial resolution (Abbe´s resolution limit) due to the so-called “memory effect”, this value always exceeds 2–5 times the feature size, with a lowest value of 52 nm. The approach is based on the investigation of the photophysics and photochemistry involved in the photopolymerization by means of the ultrafast transient absorption spectroscopy to shed some light on the inhibition processes. The expected results are the decrease of the actual size of the written features to the real nanometer resolution, ~1 nm and even more important to reduce the minimal distance of two adjacent yet separated lines (spatial resolution) to the same order of the feature size.