Optical arrangement for surface plasmon-assisted directional enhanced Raman scattering spectroscopy.

We present an optical arrangement for spectroscopy of enhanced Raman scattering assisted by surface plasmon resonance in continuous planar metallic films. Optical excitation of propagating surface plasmons (PSP) is aided by the hemispherical total internal reflectance prism in the Kretschmann geometry. In this geometry, the radiation produced by Raman scattering is directionally emitted inside the prism with the angular distribution in the shape of a hollow cone (the Kretschmann cone). The proposed configuration enables entire collection of the Kretschmann cone with the use of an elliptical mirror modified for enlarging the accessible angular range for both the incident beam and the scattered light. The spectroscopic performance of this arrangement was evaluated using the Rhodamine 6G dye as a surface enhanced Raman scattering (SERS) reporter. An evident difference in magnitudes of the enhancement factor for specific spectral lines as compared to SERS excitation by localized surface plasmon resonance (LSPR-SERS) was revealed. The origin of this difference is discussed in terms of expected distinctions between the PSP-assisted directional enhanced Raman scattering and the LSPR-SERS. Besides the spectroscopic applications, the proposed arrangement is also perfectly suited for simultaneous functioning as the SPR sensor. Integration of SERS spectroscopy with the SPR analysis shows promise as a platform for evolving an innovative analytical technique with enhanced potentialities in surface research, particularly in biochemical applications.