Polarization-switchable nanoripples fabricated on a silicon surface by femtosecond-laser-assisted nanopatterning.

The polarization ripples on many materials have been intensively studied and have yielded significant applications such as modulating light fields, building hydrophobic or hydrophilic surfaces, and fabricating tunable thermal sources. It was shown that ripples are closely dependent on the ablation threshold of laser fluence and orientation of laser polarization. Here we demonstrate that laser polarization ellipticity also represents the switching effect on the formation of ripples. Two significantly different damage morphologies, ripples and hollows, are respectively observed below and above the switching value of incident laser polarization ellipticity. Furthermore, it is demonstrated that this ellipticity switching value varies with laser pulse energy and pulse number. These intriguing phenomena are qualitatively explained using a laser-surface plasmon polariton interference mechanism. Finally, we achieve the analogous laser-assisted nanopatterning by using a femtosecond laser beam with spatially inhomogeneous polarization state, demonstrating the application potential of these switchable nanoripples in laser-assisted nanopatterning.