Femtosecond laser direct writing of complementary THz metasurfaces using a structured vortex beam

Metasurfaces, which are increasingly popular for creating ultra-thin optical components, offer a way to reduce the bulkiness of traditional optics, especially in the THz band. Typically, metasurfaces are fabricated using lithographic techniques in clean rooms, but a simpler fabrication method could expand their applicability. In this study, we present a femtosecond laser-based direct fabrication of complementary metasurfaces, highlighting the benefits of a single-step, mask-free process using structured light beams. A q-plate is used to generate an annular vortex beam with femtosecond duration, which is further tailored to imprint individual meta-atoms by perforating an Au film deposited on a Si substrate through laser ablation. This technique enables the creation of various metasurfaces designed for THz operation, as verified by full-wave simulations, featuring distinct shapes and periodicities for efficient electromagnetic radiation delivery. The fabricated devices are experimentally tested using time-domain spectroscopy, confirming the expected transmission properties and demonstrating the reliability and versatility of the proposed approach.