Metasurface mapping by photoacoustic spectroscopy

Chirality an intrinsic property of certain entities in the universe, is characterized by the absence of mirror symmetry and plays a crucial role in molecular interactions and properties. Circular dichroism (CD), measured using circulary polarized light, is an important method for chirality characterization. In this study, using a photo-acoustic spectroscopy (PAS), it allows direct measurement of local absorption, by monitoring the heat produced and transferred to the surrounding air, regardless the transmitted, reflected, and scattered light that ows away from the sample. Using a widely tunable laser source in the near-infrared and visible ranges, our PAS system incorporates numerous adjustable parameters, including wavelength, polarization, incidence angle, modulation frequency, and spatial positioning via translational and rotational stages. This set-up allows for precise spatial and spectral mapping of absorption and CD, enabling the study of extrinsic chirality in nanostructured metasurfaces, potentially addressing also important issues on homogeneity of the nanostructures, size of the domains and their orientation. These findings highlight the versatility and sensitivity of PAS for advanced chiral analysis, offering new insights into the optical behavior of nanostructures and paving the way for broader applications in nanophotonics and plasmonics.