Polarization measurements in tip-enhanced Raman spectroscopy applied to single-walled carbon nanotubes

We investigate the polarization property in tip-enhanced Raman spectroscopy by employing a radial plate consisting of four divided half-wave plates each with a different orientation of the slow axis. The radial plate provides both longitudinal (parallel to the tip axis) and lateral (perpendicular to the tip axis) polarization of the electric field on the sample plane by selecting the proper polarization of the incident field. Single-walled carbon nanotubes, which have strong polarization dependence, are investigated with this polarization control. The radial breathing mode and the G-band, which belong to different vibrational symmetries, show opposite polarization dependences.