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Title: Experimental and numerical study of plasmonic-enhanced bulk and surface nonlinear optical effects
Author: Da Silva Braz, N. V.
ISNI:       0000 0004 7964 7906
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2016
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Metallic nanostructures of dimensions below the wavelength of light show remarkable optical properties due to their ability to trap light through excitation of free-electron oscillations at a metal-dielectric interface. Coined localized surface plasmons, these are associated with a strong electro-magnetic field localization in the vicinity of the nanostructures and can find applications in integrated nonlinear optical systems given the favourable power-law scaling of nonlinear effects with the electric-field. The enhancement of surface and bulk nonlinear optical effects were investigated in this work using a variety of polarization-sensitive plasmonic devices. Investigation of bulk second- and third-order nonlinear effects in isotropic noncentrosymmetric materials were realised, both experimentally and numerically, using electric-field enhancements from complementary asymmetric cross metasurfaces. Devices were fabricated using ZnO as a nonlinear material, containing linear plasmonic resonances in the near- to mid-infrared range fully characterized using Fourier transform infra-red spectroscopy. Nonlinear optical measurements have been conducted on the complementary samples, and a tunable nonlinear optical response was observed through control of the plasmonic modes by changing the incident polarization or wavelength. A multipole expansion of the linear and nonlinear polarizations show that electric dipole interactions dominate the optical response of complementary samples. However, as result of variations in the spatial distribution of the electric-fields, predicted by Babinet's principle, significant differences in the magnetic-dipole and electric-quadrupole response between complementary samples have been observed. In particular, the device made of cross apertures in a metallic film shows the strongest enhancement of the two samples. The miniaturization, control and optimization of nonlinear optical effects are of interest for future integrated photonic systems. A numerical study of surface second-order nonlinear effects from chiral metasurfaces has been also performed, showing strong correlation between regions of superchiral light and enhanced nonlinear effects. Furthermore, a device structure has been realised with a non-reciprocal nonlinear response dependent on the handedness of the incident light. Numerical calculations based on a multipole expansion of the second-harmonic polarization, show that variations in electric quadrupolar contributions are responsible for the dichroic response.
Supervisor: Warburton, P. A. ; Panoiu, N. C. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available