Dynamic feature-size tuning in femtosecond-laser nanofabrication with phase-modulated radially polarized beams

Abstract

Femtosecond laser processing provides a versatile route for high-precision material structuring, yet the dynamic modulation of nanoscale feature sizes remains constrained by the far-field diffraction limit and insufficient control over local energy deposition. To overcome these limitations, we report a nanofabrication method based on binary pupil phase modulation of a radially polarized beam, introducing optical-field structural parameters as an active dimension for tuning the feature size of laser-processed structures. This method enables controllable modulation of single-pulse laser-processed features over a range of approximately 50–250 nm. Under an optimized phase state and energy window, this method further pushes the lower limit of size modulation to 14 nm (λ/57). Mechanistic analysis shows that this limiting size arises from the combined action of focal-field reshaping, tunnelling-ionization-dominated nonlinear material response, and threshold selection. We further extend this method to large-area nanopatterning, where the fabricated nanohole arrays and nanogratings can extend to the centimeter scale while maintaining feature sizes at the hundred-nanometer level. This method enables controllable modulation of laser-processed structures at the nanoscale and offers a route for next-generation programmable and highly controllable nanomanufacturing platforms.