Demonstration of a 3D Radar‐Like SERS Sensor Micro‐ and Nanofabricated on an Optical Fiber

A 3D surface‐enhanced Raman scattering (SERS) sensor is realized on the facet of an optical fiber. A SERS radar configuration consisting of a parabolic mirror and a 3D spherical SERS body is designed. The parabolic mirror is used to focus the excitation laser light onto the surface of the SERS body, and to collect and reflect the Raman scattered light back into the optical fiber. The SERS body's surface consists of microscale trenches and is covered with gold nanogratings and nanoparticles on a thick gold film with a thin SiO₂ spacer. Nanoscale 3D printing technology, thermal evaporation, and UV laser pulse irradiation are used to fabricate and metalize the mold of the 3D SERS radar configuration. The performance of this Au‐based SERS fiber sensor is competitive with those of Ag‐based SERS fiber sensors reported in the literature. It exhibits a detection limit of 10⁻⁶m for crystal violet in ethanol using 30 mW of 785 nm excitation (off resonance with the crystal violet electronic absorption) and 10 s acquisition time. Such a 3D scheme expands the design possibilities of SERS nanostructures on the facets of optical fibers enormously.