Phase Response of Plasmonic Nanoantennas Measured by Coherence-Controlled Holographic Microscopy

Jiří Babocký Central European Institute of Technology, Brno University of Technology, Brno, Czech Republic R&D, Tescan Orsay Holding, a.s., Brno, Czech Republic Filip Ligmajer Central European Institute of Technology, Brno University of Technology, Brno, Czech Republic Radek Kalousek Central European Institute of Technology, Brno University of Technology, Brno, Czech Republic Institute of Physical Engineering, Brno University of Technology, Brno, Czech Republic Aneta Křížová Central European Institute of Technology, Brno University of Technology, Brno, Czech Republic Institute of Physical Engineering, Brno University of Technology, Brno, Czech Republic R&D, Tescan Orsay Holding, a.s., Brno, Czech Republic Lukáš Kejík Institute of Physical Engineering, Brno University of Technology, Brno, Czech Republic Petr Dvořák Central European Institute of Technology, Brno University of Technology, Brno, Czech Republic Institute of Physical Engineering, Brno University of Technology, Brno, Czech Republic Radim Chmelík Central European Institute of Technology, Brno University of Technology, Brno, Czech Republic Institute of Physical Engineering, Brno University of Technology, Brno, Czech Republic Tomáš Šikola Central European Institute of Technology, Brno University of Technology, Brno, Czech Republic Institute of Physical Engineering, Brno University of Technology, Brno, Czech Republic

Plasmonic nanoantennas are nowadays commonly used for various applications in plasmon enhanced spectroscopy, photovoltaics and biosensing. Here, particularly enhancement of electromagnetic near fields in their vicinity upon antenna resonances are utilized. Characterization and investigation of optical properties of plasmonic nanoantennas is usually done by far-field optical spectroscopy in transmission or reflection modes. This method provides dependence of reflectance (transmissivity) of antennas on optical wavelength. Using reflectance spectra we can simply identify resonance modes of plasmonic nanoantennas by enhanced reflection at specific wavelengths. Further, these modes can be recognized by measurement of the phase of transmitted light which changes upon antenna resonant conditions significantly. However, the measurement of this effect is usually more complex and often requires a complicated post-processing. In this work we present a simple way how to measure phase response from plasmonic antennas using the coherence-controlled holographic microscopy (CCHM). CCHM belongs to the family of interferometric methods providing the quantitative phase contrast for each pixel of the observed image in real time. In combination with a tunable light source or white light and filters it is possible to perform the wavelength resolved measurements and obtain a phase spectrum for each pixel. We will demonstrate the ability to measure the phase response of arrays of disc shaped plasmonic nanoantennas fabricated on a glass substrate with resonances in the visible. Our experiments are supported by an analytical model helping to interpret the obtained results.

Left: Nanodisc shaped plasmonic antennas on a glass substrate, right: phase image of fabricated structures illuminated by white light with a 10- nm wide filter positioned at 650 nm.

jiri.babocky@ceitec.vutbr.cz