We present the design and realization of optical metasurfaces for applications in enhanced photovoltaics, controlled spontaneous emission and optical computing, and present a unique tool to characterize these geometries at deep-subwavelength spatial resolution.
The building blocks in our work are dense periodic and aperiodic arrays of crystalline silicon nanocylinders made using soft-imprint or electron beam lithography. In photovoltaic metasurfaces resonant light scattering from Si Mie scatterers causes strong (30%–40%) specular light scattering on resonance creating photovoltaic mini-modules with well-defined colours, while maintaining 90% of the photocurrent. We also demonstrate photovoltaic metasurfaces composed of pixelated arrays composed of Si Mie scatterers that create a white appearance. The colored/white solar minimodules can find application in building-integrated photovoltaics.
Next, we use a novel arbitrary-wavefront transformation concept based on metagratings composed of specially tailored light scatterers, developed by Alu et al., to create a Lambertian angular scattering response. Lambertian surfaces can find many applications in optical components, photovoltaics and more. We demonstrate how these tailored metasurfaces can be used to control spontaneous emission at distances further than the optical near-field. Further advanced optical metasurfaces can serve to perform mathematical operations on optical field distributions as we will demonstrate.
Finally, we present angle- and polarization-resolved cathodoluminescence spectroscopy as a tool to characterize optical metasurfaces using a 30 keV electron beam as the excitation source. The beam is raster-scanned over the surface and the collected optical radiation provides invaluable information on optical resonances and near-field modal coupling in the metasurfaces at nanometer spatial resolution.