# Research

 SMART POLYMERS This activity is aimed at investigating the intriguing phenomenon of light-activated mass-migration on abobenzene-containing polymers. This effect allows the realization of topographical structures on the surface of these SMART polymers. The phenomenon originates from the photo-isomerization of azobenezene units inside the polymer. Recently, we unexpectedly observed a spiral-shaped relief pattern on the surface of an azo-polymer when illuminated with a vortex laser beam. The spiral handedness of the polymer pattern is determined by the vortex one. This result is quite surprising because the common understanding is that surface photo-patterning respond to the light intensity distribution and its gradients. The intensity pattern of a vortex beam is shaped as a doughnut and carries no information whatsoever about the vortex handedness.
   NANO-IMAGING   Among all the scanning probe microscopes, Scanning Near-field Optical Microscope (NOSM) employs light and can simultaneously provide information on the morphology and on the optical properties of materials with a resolution as good as 10nm. Such technique is  crucial in studying photonic nano-devices. In fact, nowadays, fabrication techniques allow producing metasurfaces and flat optical components.    These use optically thin arrays of optical scatterers, such as antennas, with subwavelength sizes and separations, to obtain a spatially varying optical response, which molds optical wavefronts and surface waves at will. Mapping the near-field distribution of these new devices by means of NSOM microscopes allows  testing and optimizing the designing procedure.
 METASURFACES Conventional optical components are based on refraction, reflection or diffraction of light and wavefront shaping is achieved via propagation through media of given refractive indices that can be engineered to control the optical path of light beams. In this way phase and polarization changes are accumulated through propagation in refractive optical components such as lenses and waveplates. It is instead possible to engineer the wavefront by means of subwavelength structures that allow funneling all incident optical power into a single useful beam. This approach, which relies on suitable dispersion engineering of the nanostructures (metasurfaces), is highly flexible in that one can engineer the interaction between different nanostructures and light to achieve complete control of phase, amplitude and polarization response not only for a single wavelength but also for discrete spectral bands such as Red-Green-Blue (RGB) wavelengths for 3D displays.