Enhanced Raman scattering in graphene by plasmonic resonant Stokes emission

Abstract

Exploiting surface plasmon polaritons to enhance interactions between graphene and light has recently attracted much interest. In particular, nonlinear optical processes in graphene can be dramatically enhanced and controlled by plasmonic nanostructures. This work demonstrates Raman scattering enhancement in graphene based on plasmonic resonant enhancement of the Stokes emission, and compares this mechanism with the conventional Raman enhancement by resonant pump absorption. Arrays of optical nanoantennas with different resonant frequency are utilized to independently identify the effects of each mechanism on Raman scattering in graphene via the measured enhancement factor and its spectral linewidth. We demonstrate that, while both mechanisms offer large enhancement factors (scattering cross-section gains of 160 and 20 for individual nanoantennas, respectively), they affect the graphene Raman spectrum quite differently. Our results provide a benchmark to assess and quantify the role and merit of each mechanism in surface-plasmon-mediated Raman scattering in graphene, and may be employed for design and realization of a variety of graphene optoelectronic devices involving nonlinear optical processes.

Frequency pulling and line-shape broadening in graphene Raman spectra by resonant Stokes surface plasmon polaritons

“…The enhancement factors are evidently maximized where the nanostructures' resonance wavelength coincides with the corresponding G or 2D Stokes wavelength. This confirms that the Raman enhancement mechanism, herein, is dominated by the resonant Stokes emission as previously discussed [18], and the SPP resonances are adequately narrow to resolve the spectral distance between the G and 2D bands. rapidly diminish and the spectra converge to their unperturbed line shapes.…”

“…This mechanism originates from the enhanced local field produced by the SPP resonances of the nanostructures at the pump laser wavelength, which, in turn, results in the enhancement of Raman scattering due to the nonlinear dependence of the induced optical polarization on the incident field. Moreover, it has been recently demonstrated that utilizing nanostructures whose SPP resonances are tuned to the Stokes wavelengths, rather than the pump wavelength, equally efficiently enhance Raman scattering through an alternative mechanism based on increasing the optical density of states at the emission frequency [18]. This mechanism is similar in nature to the Purcell effect where the increased density of states provided by an electromagnetic cavity enhances the rate of sponta-* ghamsari@uottawa.ca † pberini@uottawa.ca neous emission from a quantum emitter [19].…”

“…The beam was focused onto an approximately 1-µm-diameter spot and was raster scanned over the samples in 100-nm steps to obtain a two-dimensional image of the Raman spectrum. More details about the fabrication and measurement steps as well as the linear response of similar devices, including reflection and transmission characteristics and their geometrical scaling rules, can be found elsewhere [18,23]. Figure 3(a) shows the measured Raman enhancement factor as a function of the nanostructures' resonance wavelength.…”

“…The enhancement factor associated with an individual nanoresonator was calculated by taking a bare graphene area without any plasmonic nanostructures as the reference according to Ref. [18]. The enhancement factors are evidently maximized where the nanostructures' resonance wavelength coincides with the corresponding G or 2D Stokes wavelength.…”

Efficient Optical Reflection Modulation by Coupling Interband Transition of Graphene to Magnetic Resonance in Metamaterials

“…where σ intra and σ inter are the intraband and interband terms of the surface conductivity of graphene, τ is the electron-phonon relaxation time, E f is the Fermi energy, and t g is the graphene thickness. The studied metamaterials could be realized in experiment with the help of advanced nanofabrication technology [83]. Firstly, the silver substrate and the silica layer are prepared by thermal evaporation.…”