Resonant Mirror Enhanced Raman Spectroscopy

A resonant mirror as a high-Q dielectric resonator can accumulate a strong evanescent field at its surface, and this field has been proposed for surface/interface Raman enhancement applications for a while. However, the theoretically predicted large Raman enhancement effect of a resonant mirror had never been experimentally demonstrated until our work reported here, primarily due to the difficulties confronting the experimentalists in determining the resonant conditions for this optical device and optimizing the collection efficiency of Raman radiation from molecules at its surface. In this study, taking advantage of the rationally designed and well-fabricated high-quality planar dielectric optical waveguides, and overcoming the two difficulties aforementioned through the use of m-line spectroscopy and waveguide-coupled directional Raman emission techniques, we present the first experimental demonstration of resonant mirror enhanced Raman spectroscopy (RMERS). Considerable signal enhancement that enabled the polarization-division multiplexing (PDM) Raman detection of copper phthalocyanine (CuPc) ultrathin films and cytochrome c (Cyt c) monolayer deposited at the waveguide surface has been achieved. Considering its high Raman enhancement capability, outstanding PDM Raman detection ability, and good affordability, RMERS is believed to be a promising tool for the in situ Raman analysis of analytes on the dielectric flat surfaces and interfaces under ambient conditions.