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Metasurfaces: a nanophotonic platform for full control of light in space and time

Leonardo de S. Menezes - Chair in Hybrid Nanosystems - Faculty of Physics, Ludwig-Maximilians University Munich, Germany Photonics is the branch of science dedicated to creating and manipulating photons, exploiting their properties for example in the realization of physical processes and protocols, as well as detectors and sensors. Some years ago, photonics felt the need of a paradigm change, following the steps of electronics, in which extreme miniaturization is essential to make electronic circuits faster and energy saving. This miniaturization in photonics led to the field of nanophotonics, which aims the same as photonics, but at scales typically given by the wavelength of light, that is, a nanometric scale. One of the essential tasks of nanophotonics is to develop structures able to substitute bulky optical elements in devices and platforms that get smaller and smaller. In this framework, metasurfaces play an essential role, being already a reality. Metasurfaces are artificial bidimensional structures formed by subwavelength sized elements, called metaatoms (or metamolecules), aiming at locally controlling the amplitude and/or the phase of an incoming light beam such that the farfield resulting from the scattering of all illuminated metaatoms presents desired spatial and temporal dependences. The spatial tailoring of the resulting scattered farfield can be done by nanostructuring the metatatoms on the metasurface, while its temporal tailoring can be done, e.g., by using phase change materials to fabricate the metaatoms: by inducing the phase transition in the metaatoms, one may significantly change the real and/or imaginary parts of their refractive index, thus changing their scattering properties and bringing tunability to the metasurface. In this colloquium, I will present the concept of metasurface, give some examples of applications, and discuss how a metasurface composed by nanodisks made from vanadium dioxide (a phase change material triggered by temperature) can be used to achieve a tunable metasurface in the visible range.