Modulating the periodicity of plasmonic lithography by high-repetition-rate laser-driven heat accumulation.

We experimentally demonstrated the fabrication of highly regular laser-induced periodic surface structures (LIPSSs) on an amorphous silicon film coating on a copper substrate. Driven by femtosecond laser-plasmon interference-induced photochemical reactions, we achieved an increase of the LIPSS periodicity from 752 to 870 nm by heating the hybrid film from 298.15 to 368.15 K, yielding a thermal sensitivity of ~15.5 nm$\,\cdot\,\text{10K}^{-1}$. To achieve localized thermal regulation, we further tuned the periodicity of LIPSS from 752 to 830 nm by varying the laser repetition rate from 100 to 1800 kHz with a tuning sensitivity of ~4 nm$\,\cdot\,$100 $\text{kHz}^{-1}$. This increase is attributed to heat accumulation among the inter-pulses, which modifies the wavelength of the surface plasmon polaritons. We developed a physical model for numerical calculations to investigate the dependence of the heat accumulation on the repetition rate. This study provides a practical and convenient approach for modulating the periodicity of nanostructures in femtosecond laser plasmonic lithography, offering potential applications in nanophotonics and other related fields.