Near-field second-harmonic generation from gold nanoellipsoids

Second‐harmonic generation from single gold nanofabricated particles is experimentally investigated by a nonlinear scanning near‐field optical microscope (SNOM). High peak power femtosecond polarized light pulses at the output of a hollow pyramid aperture allow for efficient second‐harmonic imaging, with sub‐100‐nm spatial resolution and high contrast. The near‐field nonlinear response is found to be directly related to both local surface plasmon resonances and particle morphology. The combined analysis of linear and second‐harmonic SNOM images allows one to discriminate among near‐field scattering, absorption and re‐emission processes, which would not be possible with linear techniques alone. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)