Surface-enhanced Raman scattering at a planar dielectric interface beyond critical angle.

Area of Science:

• Optics and Photonics
• Surface Science
• Spectroscopy

Background:

• Light propagation in dielectric media is limited by total internal reflection beyond the critical angle.
• Evanescent waves can propagate beyond the critical angle at dielectric interfaces.
• Surface-enhanced Raman scattering (SERS) is a sensitive technique for molecular detection.

Purpose of the Study:

• To quantify the polarization and angle dependence of SERS intensity beyond the critical angle.
• To investigate light propagation and scattering phenomena at dielectric interfaces using SERS.
• To validate a classical dipole model for SERS near an interface.

Main Methods:

• Acquisition of Raman spectra of thiocyanate molecules adsorbed on silver nanoparticles.
• Utilizing evanescent wave excitation and detection at the water-glass interface.
• Analysis of SERS signal polarization and scattering angle dependence.

Main Results:

• SERS intensity was successfully measured beyond the critical angle using evanescent excitation.
• The polarization and angle dependence of the SERS signal were quantified.
• Experimental results showed agreement with a classical dipole radiation model.

Conclusions:

• Evanescent wave excitation overcomes critical angle limitations for light propagation.
• The study provides a quantitative understanding of SERS beyond the critical angle.
• A classical dipole model effectively describes SERS phenomena near dielectric interfaces.