Design and construction of a Raman microscope and characterization of plasmon-enhanced Raman scattering in graphene

Nanometallic structures efficiently convert light to surface plasmon-polaritons (SPPs) localized to ultra-small volumes. Such structures provide highly enhanced fields and are of interest in applications involving SPP-enhanced nonlinear optics. We report the design and construction of a spontaneous Raman microscope augmented with in situ reflectance measurement capabilities, and demonstrate its use for nonlinear plasmonics. The structures investigated consist of rectangular gold nanoantennas on graphene on a SiO2/SiSiO2/Si substrate. Specifically, SPP-enhanced Raman scattering from graphene is investigated using nanoantennas that are spectrally aligned with the Stokes wavelength of the graphene 2D peak. We use the microscope to demonstrate Raman scattering enhancement in graphene based on plasmonic resonant enhancement of the Stokes emission, where a maximum cross-sectional gain of ∼500∼500 per antenna was measured. We also measure the reflectance response of nanoantenna structures of different dimensions (length, width) to determine how the resonant wavelength shifts with dimensions and ensure spectral alignment with the Stokes wavelengths of interest.