Sub-diffraction limited Coherent Anti-Stokes Raman scattering from the tip of a plasmonic nanocone

CARS measurements in combination with plasmonic nanoCone


​​In this paper we demonstrate, for the first time to our knowledge, the possibility to detect the Coherent Anti-Stokes Raman Scattering (CARS) signal from the tip of a plasmonic nanocone with sub-diffraction resolution. Pump and Stokes beam from two intrinsically synchronized 80MHz ps pulsed sources have been converted to radial polarization and coupled to the propagating modes of a metallic nanocone. The two plasmonic waves induced at the surface of the nanocone propagated up to its distal apex while experiencing adiabatic compression of the electromagnetic field. The nonlinear interaction of the two beams at the tip led to the generation of an Anti-Stokes signal that could be collected in far-field with a microscope objective and measured. The emission spectrally shows to be consistent with the expected CARS signal arising from the molecules previously deposited at the tip of the nanocone, hence demonstrating its intrinsically sub-diffraction limit origin. This result paves the way to the development of nonlinear coherent Raman spectroscopy at nanoscale.​