3D cartography of light scattered by plasmonic nanostructures at resonance obtained by digital heterodyne holography

摘要

Nanoantennas are the direct extension of conventional radio and microwave antennas to the visible frequency range and can be used to convert optical radiation into localized energy and resonantly enhance light scattering [1,2]. Here, we present a highly sensitive full-field imaging technique based on digital heterodyne holography [3] which allows the measurement of both amplitude and phase. This results in the 3D mapping of light scattered by plasmonic nanostructures at specific resonance wavelengths. Spectral and spatial properties of the field are compared to numerical simulations. The experimental setup is based on a Mach-Zehnder interferometer. The laser beam is separated in reference and object arms, frequency shifted by two acousto-optical modulators. The sample is placed on a prism and illuminated in total internal reflection configuration to achieve dark field illumination. The scattered field is collected by a microscope objective (100x magnification, NA= 0.85 in air) and reaches the CCD camera where it interferes with the reference beam in an off-axis manner. The reconstruction of the hologram is achieved numerically.