White-light total internal reflection microscopy for characterizing the optical properties of Ag-coated optical fiber...

The optical properties of the metallized tips used in tip-enhanced Raman spectroscopy (TERS) are vital to resonance enhancement. A white-light scattering-spectrum measuring setup based on total internal reflection microscopy is developed to characterize the optical responses of the metallized tips. The scattering spectra of the Ag-coated optical fiber tips are measured as a demonstration of the methodology and the performance of the setup. A prominent resonance band of 500-550 nm is observed experimentally, which can be interpreted as the result of the excitation of the localized surface plasmon resonance at the Ag-coated optical fiber tip. The optical responses of the Ag-coated optical fiber tips are simulated by a three-dimensional finite-difference time-domain method and the results are compared with the experiments. This method has great application potential in the selection and design of high-performance metallized tips for TERS and other apertureless near-field optical microscopy.