Physics

Adrian Agreda
Université Bourgogne Franche-Comté

Abstract: 

Plasmonic metal nanoantennas are attracting an ever growing attention since their ability to strongly enhance electromagnetic fields and consequently improve weak nonlinear optical processes that take place on the nanoscale. Recent works highlighted that coherent second-harmonic generation emitted from optical antennas loaded with a nonlinear material can be controlled by electrostatic means.

The objective of this work is to investigate the influence of a time-varying electric field on the intrinsic incoherent nonlinear response of an unloaded electrically-contacted gap antennas. In particular, we are interested at modulating the yield at which incoming photons are up-converted by means of an electrical control of the surface charge density.

In our experiment, gold optical gap antennas are excited with a tightly focused near-infrared femtosecond laser beam resulting in the broadband emission of nonlinear photo-luminescence (N-PL). A nano-capacitor is formed by applying an electric field between the two constitutive nanowires of the optical antenna, creating thereby localized regions of electron accumulation and electron depletion.

We show that the evolution of the N-PL yield depends on the surface charge density, and consequently the precise location of the focused laser beam on the antenna with respect to the polarity and the strength of the controlled field. A modulation depth larger than 100% is observed in the N-PL signal for a few volts. We will discuss the mechanisms at play and their effects on the bandwidth at which the nonlinear signal can be modulated.