Amplifying Plasmonic Metasurfaces: Optical gain for response control, metasurface lasing and symmetry breaking

Metasurfaces assert control over light at scales shorter than the wavelength and they are often composed of metallic plasmon-resonant nanoparticles. We study amplifying plasmonic metasurfaces – metasurfaces with with embedded optical gain – as these offer a versatile experiment to study seminal problems in condensed matter physics. We first present the development of a new ultrafast pump-probe Fourier microscope setup to study amplifying metasurfaces. Then, we present a theoretical study of singular responses in the reflection of light from a scattering plasmonic metasurface with gain. Considering optical gain as opposed to absorption, and using a transfer matrix model to calculate reflectivity, we find that gain can induce both perfect absorption and perfect amplification. Subsequently, we report on the first experimental observation of spontaneous symmetry breaking (SSB) in plasmonic metasurface lasers, that originates from K- and K’-point mode competition. By capturing single-shot emission in Fourier and real space, we simultaneously map the two order parameters of the symmetry breaking. Followingly, we present an experiment on the programmability of laser emission through spatial and dynamic control of the gain, achieved by projecting the optical pump on a digital micromirror device. We study the relation between real-space laser shape, Fourier-space vortex beams, and local spatial intensity distribution in the SSB process. Finally, we study dense metasurfaces with beyond-light-line dispersions. We make these dispersions experimentally visible by bandfolding, induced by superlattice size perturbations of the scatterers. In fluorescence enhancement experiments, we find that folding K-point dispersion creates a narrow plasmon mode with extremely high quality factor.