New Frontiers of Infrared Optics: Tunable Metamaterials Studied at the Frascati National Laboratory of INFN

An important contribution to new developments in infrared optics has come from the Frascati National Laboratory (LNF) of the Italian National Institute of Nuclear Physics (INFN), where the experimental characterization of an innovative metamaterial was conducted at the Dafne-Luce facility.
This research, a result of collaboration between a group from the Department of Basic and Applied Sciences for Engineering (Sapienza University of Rome) and published in the journal Scientific Reports, focuses on a hybrid metamaterial, which is an artificial material made up of a thin film of vanadium dioxide (VO₂) combined with a matrix of gold nanodisks (on the scale of billionths of a meter).

VO₂ is an interesting material because it undergoes a phase transition, changing from a semiconductor state to a metallic state when heated to a relatively low temperature, around 68 °C. This structural change results in significant modifications to its electrical, thermal, and optical properties.

At the Dafne-Luce facility, the experimental characterization of the metamaterial was carried out using a FTIR (Fourier-transform infrared) spectrometer coupled with a microscope. Specifically, the amount of light reflected in the infrared region (wavelengths 3 – 5 μm) from the surface of the metamaterial was analyzed as the temperature varied from ambient to 100 °C.

The experimental results showed that when VO₂ is in its semiconductor state (at room temperature), it exhibits strong absorption in the mid-infrared (4.72 μm). As the material is heated, the absorption gradually shifts toward longer wavelengths, reaching 5.43 μm at 66 °C. This shift of nearly 1 μm demonstrates the significant variation in the optical response of the metamaterial as a function of temperature. The researchers also observed that the process is reversible, with a return to the initial response upon cooling the sample.

This research opens up interesting prospects for various applications, such as thermal shielding systems, adjustable infrared optical devices, and other technologies that require precise control of infrared light.

Petronijevic, E., Larciprete, M.C., Centini, M. et al. Active infrared tuning of metal–insulator-metal resonances by VO₂ thin film. Sci Rep 14, 25324 (2024). https://doi.org/10.1038/s41598-024-75430-0