A feasibility study on scanning imaging of tip-enhanced Raman spectroscopy using a spiral plasmonic lens

In the previous work, to achieve the ultra-compact configuration and the lab-on-a-chip technique of tip-enhanced Raman spectroscopy (TERS), a novel TERS based on symmetry breaking plasmonic lens (PL) excitation has been theoretically and experimentally verified. In such a system, the PL and the metal probe together constitute the sensor of the Raman signal. Since the focused surface plasmon polariton field excited by the PL has the characteristic that the main energy is concentrated in the longitudinal direction and has a subwavelength size, the introduction of plasmonic lenses can improve the detection sensitivity of the setup. However, this relevant device could only achieve Raman signals at specific points of the sample, and could not achieve scanning imaging of the sample. In this paper, we propose a method of using a spiral PL as an excitation source generator of TERS based on the previous work, which can achieve scanning imaging of sample Raman scattering signals by rotating the plasmonic lens and changing the incident angle of the circularly polarized light. The simulation carried out using the finite-difference time-domain method not only verifies the feasibility of this TERS setup, but also explains the influence of the initial radius and number of turns of the spiral PL on the results.