Revealing the electromagnetic mechanism of coherent light scattering in a single hot spot of plasmonic nanoantennas

P. ALBELLA; P. ALONSO; M. SCHNELL; J. CHEN; F. HUTH; A. GARCIA-ETXARRI; F. CASANOVA; F. GOLMAR; L. ARZUBIAGA; L. HUESO; J. AIZPURUA; R. HILLENBRAND

San Diego

Conferencia; SPIE optics+photonics 2012; 2012

International Society for optics and photonics SPIE

Light scattering by nanoscale objects - such as atoms, molecules or nanoparticles - provides a valuable tool to obtain spectroscopic information on the electronic, optical and chemical properties of the object. When molecules or nanoparticles (objects) are placed at a hot spot (antenna), the incident light is converted into nanoscale confined and strongly enhanced optical fields (?hot-spots?), thus acting as the optical analogue of an antenna. In this way, the Raman scattering, fluorescence or infrared absorption can be dramatically enhanced obtaining enormous signal enhancement factors of more than . This effect is possible because the Raman intensity scales with the fourth power of the local field enhancement at the antenna surface. Although this law is widely used, its underlying electromagnetic scattering mechanism is still awaiting for a quantitative verification. Here we use the light elastically scattered from an individual object located in a well defined hot-spot of single nanoantennas as a new approach to resolve the double role of the antenna in the scattering process (scattering both incoming and outgoing radiation). We show for the first time experimental evidence that the scattering off the object is doubly enhanced by the presence of the antenna, and that the underlying electromagnetic mechanism in antenna-assisted elastic scattering is analogous to that in SERS. We also discuss how the access to the phase shift induced by the antenna, provides an additional novel fingerprint of this scattering mechanism.