title: Mapping local field enhancements at nanostructured metal surfaces by second-harmonic generation induced in the near field.
abstract: We report on an aperture scanning near-field optical microscope in which femtosecond pulses are coupled to a hollow-pyramid aperture sensor. Such probe displays high throughput and preserves pulse duration and polarization, enabling the achievement of sufficiently high peak power in the near field to perform nonlinear optics on the nanoscale. We use the system to observe the nonlinear optical response of nanostructured metal surfaces with sub-100-nm spatial resolution. We study second-harmonic generation from gold nanoparticles both isolated and in high-density patterns, highlighting a strong dependence of the generation efficiency on the shape and on the fine structure of the nanoemitter. In particular, we present results on closely packed gold triangles as well as on nanoellipsoids with different local surface plasmon resonances.
authors.affiliation: ULTRAS-CNR-INFM, Physics Department, Politecnico di Milano, Piazza Leonardo da Vinci 32, L-20133 Milan, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Celebrano
authors.forename: M
authors.initials: M
authors.lastname: Zavelani-Rossi
authors.forename: D
authors.initials: D
authors.lastname: Polli
authors.forename: G
authors.initials: G
authors.lastname: Cerullo
authors.forename: P
authors.initials: P
authors.lastname: Biagioni
authors.forename: M
authors.initials: M
authors.lastname: Finazzi
authors.forename: L
authors.initials: L
authors.lastname: Duò
authors.forename: M
authors.initials: M
authors.lastname: Labardi
authors.forename: M
authors.initials: M
authors.lastname: Allegrini
authors.forename: J
authors.initials: J
authors.lastname: Grand
authors.forename: P-M
authors.initials: PM
authors.lastname: Adam