Light-matter interactions in lossy and lossless media

• Main Author: Cambiasso, Javier
• Other Authors: Maier, Stefan ; Kim, Myungshik
• Published: Imperial College London 2017
• Subjects: 530
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.726964

Light-matter interactions lie at the core of modern technologies. Different decay channels get activated depending on the structure of matter used and on the properties of the exciting light. In particular, nano-antennas are used as the quintessential object to redistribute the energy of single-photon emitters in the nano-scale or of free-electrons oscillations in metals. Two different kind of nano-antennas are studied: metallic (lossy) and dielectric (lossless). Metallic nano-antennas are shown to be applicable to technologies benefiting from enhancement of both radiative and non-radiative properties. In stark contrast, certain dielectric nano-antennas are essentially lossless in the visible regime, which benefits their coupling to far-field modes. The metallic nano-antennas used in this work are either asymmetric nano-cavities or the ubiquitous bow-tie antenna. With the former we show enhancement of the radiative rate of single photon emitters located in the neighbourhood of the strongly modified electromagnetic environment. Here, two competing processes collude to either enhance or quench the coupling to the far-field. As will be shown via simulations, these two scenarios are strongly wavelength dependent and two very differentiated regions can be recognised where one overwhelms the other. Contrariwise, the bow-tie antennas are used to enhance the opposite effect: non-radiative channels exclusively. Here it is experimentally demonstrated that surface plasmon polaritons excited in the nano-structure can decay into hot carriers, instead of far-field radiation. A sub-diffraction mapping of the rate of hot electron generation is traced by depositing nano-particles and analysing many scanning electron micrographs. In order to show that nano-photonics also has the potential to get rid of losses, we investigated the possibility of applying gallium phosphide nano-antennas as efficient far-field out-couplers. A comparison between metallic and dielectric nano-antennas is carried out using a unified theory and finally experimental results corroborate the large enhancement predicted by the theory of the fluorescence rate of single-photon emitters located around the scatterers.