High-power infrared plasmonic nano-devices

Abstract

Many modern optical nano-devices rely on the excitation of surface plasmon polaritons or localized surface plasmons at the metal-dielectric interfaces. The arising plasmonic effects can then be used for sub-wavelength confinement of optical radiation, production of negative refractive index material, and strong field enhancement of particular components of the incident electric field. Due to the lossy nature of metal, some portion of the electromagnetic energy inevitably converts into heat, which, in case of plasmonic resonances, can thermally damage fragile nano-structures. This thesis experimentally and theoretically investigates the optical properties and heat resistance of infrared nano-antennas, metamaterial slot waveguides and fishnet metamaterials by numerically analyzing or exposing them to incident laser light. More precisely, these studies include: 1) Comparing the performance of titanium and gold dipole nano-antennas. It is shown that titanium-based structures can handle more than 18 dB greater power densities, thereby, being able to withstand 7 times higher electric fields than gold counterparts of similar size. 2) Numerically investigating metamaterial-based silica-filled slot waveguides, whose geometry and judicious choice of constituent materials enable both improvement of their optical properties and operation in high-power regimes. It is found that the proposed design also provides a balanced solution between strong electric field confinement and reasonably low propagation losses. 3) Analysing light-medium interactions in fishnet metamaterial, which has an additional absorbing titanium layer. The experiments demonstrate that the amount of incident optical radiation required to damage these metamaterials reduces by nearly 50% and the exposure leads to various thermal deformations of illuminated surfaces even at moderate laser powers. Thereby, it is shown that all considered devices are suitable for high-power operation by either having high melting thresholds (nano-antenna and slot waveguide) to withstand strong incident electromagnetic fields or, on contrary, being very temperature dependent and, thus, having a potential to be used as thermal sensors (fishnet metamaterial).