title: Role of antenna modes and field enhancement in second harmonic generation from dipole nanoantennas.
abstract: We study optical second harmonic generation from metallic dipole antennas with narrow gaps. Enhancement of the fundamental-frequency field in the gap region plays a marginal role on conversion efficiency. In the symmetric configuration, i.e., with the gap located at the center of the antenna axis, reducing gap size induces a significant red-shift of the maximum conversion efficiency peak. Either enhancement or inhibition of second-harmonic emission may be observed as gap size is decreased, depending on the antenna mode excited at the harmonic frequency. The second-harmonic signal is extremely sensitive to the asymmetry introduced by gap's displacements with respect to the antenna center. In this situation, second-harmonic light can couple to all the available antenna modes. We perform a multipolar analysis that allows engineering the far-field SH emission and find that the interaction with quasi-odd-symmetry modes generates radiation patterns with a strong dipolar component.
authors.forename: Domenico
authors.initials: D
authors.lastname: de Ceglia
authors.forename: Maria Antonietta
authors.initials: MA
authors.lastname: Vincenti
authors.forename: Costantino
authors.initials: C
authors.lastname: De Angelis
authors.forename: Andrea
authors.initials: A
authors.lastname: Locatelli
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Haus
authors.forename: Michael
authors.initials: M
authors.lastname: Scalora