Fiber Vector Light-Field-Based Tip-Enhanced Raman Spectroscopy

Tip-enhanced Raman spectroscopy (TERS) has been extensively employed to investigate the light-matter interaction at the nanoscale. However, the current TERS strategies lack the ability to excite the low-background inhomogeneous electromagnetic field with significant enhancement of electric field, electric field gradient, and optomagnetic field, simultaneously. To overcome this, we developed a fiber vector light-field-based TERS strategy aimed at exploring the multipole Raman scattering processes of molecules. By modulating the excitation power, we have observed for the first time the Stark effect associated with Raman-forbidden transitions, revealing a strong electric-field gradient and optomagnetic effect within the plasmon cavity. Furthermore, by manipulating the plasmon tip to minimize the nanogap, we demonstrate that splitting occurs in the dipole Raman spectrum, indicating that the plasmon cavity enters a strong coupling regime. This fiber vector light-field-based TERS approach offers a unique opportunity to investigate weak matter responses with potential applications in single-molecule spectroscopy, sensors, and catalysis monitoring.