Hybrid Grating-Hole Nanostructures Produced by Spatiotemporal Modulation of Femtosecond Lasers: Implications for Near-Field Enhancement

Here, we report a method or one-step generation of peculiar hybrid grating-hole nanostructures on Fe-based metallic surfaces upon irradiation with spatiotemporally modulated femtosecond lasers, i.e., orthogonal linear polarizations of time-delayed double laser beams are manipulated into a tightly spatial energy distribution by optical diffraction. It is surprisingly found that the induced surface structures not only present the highly uniform appearance but also consist of two different geometric components: the ablation subwavelength grating pattern with a spatial period of 707 nm and the well-distributed nanohole arrays on the ridge areas. Remarkably, both the grating length and the nanohole numbers can be controlled by varying the laser energy fluence. Theoretical analyses reveal that the formation of these structures can be attributed to the surface plasmon excitation and the light scattering of finite-length microstructures. Moreover, further simulation and experimental results clearly demonstrate the near-field enhancement effect of such laser-induced structures, which provides a promising way toward on-demand manipulation of the light response and detection in metadevices.