Development of coherent light sources at the nanoscale using optical metamaterials

Coherent nanoscale optical sources are of paramount importance to achieving all-optical communication. Several optical processes are inherently coherent and could be employed to achieve narrow-band light generation, including stimulated emission and nonlinear optical processes, such as second harmonic generation. Plasmonic resonances in metallic nanostructures provide a path to both confine such processes to the nanoscale, while also enhancing local electromagnetic fields to increase their efficiencies. In this thesis, we have developed two platforms for generating coherent light at the nanoscale. The first device is a unique metasurface that employs electric and magnetic resonances for TM-polarized light to greatly enhance second harmonic generation. Due to large tunability of the magnetic resonance, we can align the resonances at fundamental and second harmonic frequencies to achieve an enhanced conversion efficiency reaching up to 1.32E-10. The second device uses highly uniform gold nanowire arrays, which constitute a unique type of metamaterial with hyperbolic dispersion, to achieve efficient lasing. Such materials have a singularity in the local density of states, and therefore offer broadband means to enhance spontaneous emission of quantum emitters in their vicinity. This enhanced emission couples into lasing modes in the nanorod arrays, giving rise to low-threshold and highly-efficient lasing action. Here we have experimentally demonstrated the advantage of hyperbolic metamaterials to achieve lasing action by its comparison with that obtained in a metamaterial with elliptic iso-frequency surfaces. Both the metasurface as well as the hyperbolic metamaterial serve as platforms for nanoscale coherent photon sources in a broadband wavelength range