Customized PVA/AA diffraction gratings by high repetition rate femtosecond direct laser writing

In this work, we investigate the behavior of poly(vinyl alcohol)/acrylamide photopolymers (PVA/AA) under high repetition rate (1 kHz – 1 MHz), multipulse (1 – 20), femtosecond (450 fs) laser irradiation at λ=515 nm, varying fluence values from 0.005 to 1.24 J/cm². Our results reveal that a wide range of nano/microstructures with varying heights and shapes can be induced, as a consequence of monomer diffusion and swelling effects. Furthermore, we demonstrate that by adjusting the irradiation parameters, it is possible to achieve precise control over the fabricated structures, enabling potential applications not only in optics, but also in tribology and cell adhesion and growth. As an application of these results, we successfully fabricated high-period diffraction gratings at high repetition rates with diffraction efficiencies close to the theoretical maximum. These findings provide new insights into the ultrafast lasermatter interaction in photopolymers and open new scenarios for the fabrication of functional polymeric surfaces.