Imaging of second harmonic generation in the near field of ellipsoidal gold nanoparticles

In this paper, a nonlinear aperture SNOM is used. It is based on a hollow pyramid tip, providing polarized high-peak-intensity femtosecond light pulses in the near field. Second harmonic (SH) images from single gold nanoellipsoids with various aspect ratio are obtained, with high contrast and sub-100-nm spatial resolution. The nonlinear response strongly depends on both LSP resonances and particle morphology. Moreover simultaneous acquisition of both FW and SH provides clear and unambiguous information on scattering, absorption and re-emission processes at the particles.