Roberto Li Voti

Bio: Roberto Li Voti is an academic researcher from Sapienza University of Rome. The author has contributed to research in topics: Metamaterial & Emissivity. The author has an hindex of 14, co-authored 58 publications receiving 571 citations.

Chiral light intrinsically couples to extrinsic/pseudo-chiral metasurfaces made of tilted gold nanowires

Abstract: Extrinsic or pseudo-chiral (meta)surfaces have an achiral structure, yet they can give rise to circular dichroism when the experiment itself becomes chiral. Although these surfaces are known to yield differences in reflected and transmitted circularly polarized light, the exact mechanism of the interaction has never been directly demonstrated. Here we present a comprehensive linear and nonlinear optical investigation of a metasurface composed of tilted gold nanowires. In the linear regime, we directly demonstrate the selective absorption of circularly polarised light depending on the orientation of the metasurface. In the nonlinear regime, we demonstrate for the first time how second harmonic generation circular dichroism in such extrinsic/pseudo-chiral materials can be understood in terms of effective nonlinear susceptibility tensor elements that switch sign depending on the orientation of the metasurface. By providing fundamental understanding of the chiroptical interactions in achiral metasurfaces, our work opens up new perspectives for the optimisation of their properties.

Nanolayered lightweight flexible shields with multidirectional optical transparency

Abstract: New nanolayered coatings are designed and deposited on flexible plastic substrate having the thickness of 100 /spl mu/m, in order to realize lightweight ultrathin transparent shielding foils. The structure of the coating is optimized considering three figures of merit: the average transmittance in the visible range for normal incidence, the normalized average transmittance for oblique incidence at 550 nm, and the transmittance quality factor. The nanotechnology exploited for the deposition of the transparent metals is the dual ion beam sputtering. Tests of durability, optical transmission, and shielding effectiveness demonstrate that the film has a high adhesion under mechanical solicitation, high resistance against aging, peak transmittance in the visible range higher than 70%, omnidirectional properties in the range 0/spl deg/-60/spl deg/, and shielding effectiveness of 40 dB up to 6 GHz.

Tomographic reconstruction of picosecond acoustic strain propagation

Abstract: By means of an ultrafast optical technique, picosecond acoustic strain pulses in a transparent medium are tomographically visualized. The authors reconstruct strain pulses in Au-coated glass from time-domain reflectivity changes as a function of the optical angle of incidence, with ∼1ps temporal and ∼100nm spatial resolutions.

Correlation between in situ structural and optical characterization of the semiconductor-to-metal phase transition of VO2 thin films on sapphire.

Abstract: A detailed structural investigation of the semiconductor-to-metal transition (SMT) in vanadium dioxide thin films deposited on sapphire substrates by pulsed laser deposition was performed by in situ temperature-dependent X-ray diffraction (XRD) measurements. The structural results are correlated with those of infrared radiometry measurements in the SWIR (2.5-5 μm) and LWIR (8-10.6 μm) spectral ranges. The main results indicate a good agreement between XRD and optical analysis, therefore demonstrating that the structural transition from monoclinic to tetragonal phases is the dominating mechanism for controlling the global properties of the SMT transition. The picture that emerges is a SMT transition in which the two phases (monoclinic and tetragonal) coexist during the transition. Finally, the thermal hysteresis, measured for thin films with different thickness, showed a clear dependence of the transition temperature and the width of the hysteresis loop on the film thickness and on the size of the crystallites.

Photonic crystals

Abstract: The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

Principles Of Optics Electromagnetic Theory Of Propagation Interference And Diffraction Of Light

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Size effects in the structural phase transition of VO2 nanoparticles

Abstract: We have observed size effects in the structural phase transition of submicron vanadium dioxide precipitates in silica. The VO 2 nanoprecipitates are produced by the stoichiometric coimplantation of vanadium and oxygen andsubsequent thermal processing. The observed size dependence in the transition temperature and hysteresis loops of the semiconductor-to-metal phase transition in VO 2 is described in terms of heterogeneous nucleation statistics with a phenomenological approach in which the density of nucleating defects is a power function of the driving force.

Chirality and Chiroptical Effects in Metal Nanostructures: Fundamentals and Current Trends

Abstract: Throughout the 19th and 20th century, chirality has mostly been associated with chemistry. However, while chirality can be very useful for understanding molecules, molecules are not well suited for understanding chirality. Indeed, the size of atoms, the length of molecular bonds and the orientations of orbitals cannot be varied at will. It is therefore difficult to study the emergence and evolution of chirality in molecules, as a function of geometrical parameters. By contrast, chiral metal nanostructures offer an unprecedented flexibility of design. Modern nanofabrication allows chiral metal nanoparticles to tune the geometric and optical chirality parameters, which are key for properties such as negative refractive index and superchiral light. Chiral meta/nano-materials are promising for numerous technological applications, such as chiral molecular sensing, separation and synthesis, super-resolution imaging, nanorobotics, and ultra-thin broadband optical components for chiral light. This review covers some of the fundamentals and highlights recent trends. We begin by discussing linear chiroptical effects. We then survey the design of modern chiral materials. Next, the emergence and use of chirality parameters are summarized. In the following part, we cover the properties of nonlinear chiroptical materials. Finally, in the conclusion section, we point out current limitations and future directions of development.