Title

Super-resolution and nonlinear absorption with metallodielectric stacks

Author

Nkorni Katte

Date of Award

2011

Degree Name

Ph.D. in Electro-Optics

Advisor/Chair

Advisor: Joseph W. Haus

Abstract

We investigate sub-wavelength imaging, i.e. super-resolution, in metal-dielectric film systems, which are simply referred to as metallodielectrics. Our simulations incorporate experimentally derived material dielectric dispersion properties across the visible region. For demonstration purposes we designed metallodielectric stacks for super-resolution containing GaP and TiO2, dielectric films, and either Ag or Au as the metallic materials. Using the known optical properties of the constituent materials found designs that could be good candidates for super-resolution. We did not have the resources to fabricate these samples; however, based on our computer simulations we are confident that the designed samples would produce super-resolution approaching one-twentieth of a wavelength in air. We examined for the first time the broad bandwidth of the super-resolution phenomenon in metallodielectrics. We validate the results using the finite element method (FEM) and the transfer matrix method (TMM). We also show that the measurement of super-resolution is highly dependent on the distance of the probe from the exit surface; high resolution at the exit plane can quickly decay with a few tens of nanometers when high resolution is sought. Secondly we numerically studied the nonlinear optical transmission of an optical beam through heterogeneous metallodielectric stacks under the action of nonlinear absorption. One film layer is a metal and the other layer is a dielectric; the heterogeneous material is called a metallodielectric stack (MDS). In these studies we also used applied FEM with two-dimensional transverse effects and TMM simulation techniques. Our samples consisted of Ag/ZnS, Ag/SiO2 and Cu/ZnS. We numerically simulate using two transverse dimensions in our FEM codes, Z-scan experiments for two different MDS designs and draw general observations from these cases. We experimentally examined the nonlinear absorption effect in samples of Ag/SiO2 when irradiated by a femtosecond pulse width beam. There is a significant nonlinear enhancement effect observed in high transmission spectral regimes, which is attributed to field confinement in the metal layers. We showed how the nonlinear absorption varies with wavelength, which changes the field penetration within the stack layers. These results can be applied for of optical limiters and switches.

Keywords

Optical films Optical properties Computer simulation, Nanostructured materials Optical properties Computer simulation, High resolution imaging Computer simulation, Ellipsometry

Rights Statement

Copyright 2011, author

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