Laser-Based Reshaping of Self-Organized Metasurfaces of Supported Ag Nanoparticles for Encoding Tunable Linear Dichroism Patterns

Two-dimensional (2D) metasurfaces have emerged as a promising platform for optical field manipulation at the nanoscale. To realize their considerable potential, fast, facile, and scalable manufacturing techniques are needed. Here, we put forward such a technique to transform an isotropic self-organized 2D ensemble of supported Ag nanoparticles (NPs) into a functionalized metasurface with tailor-made patterns of linear dichroism (LD). Nanostructured films comprising densely packed Ag NPs with a wide distribution of their sizes, shapes, and nearest neighbor separations were obtained via vacuum deposition of Ag vapors on a glass substrate at room temperature. Then, under the action of linearly polarized pulsed laser illumination, selective heating and reshaping of NPs are achieved. Thus, depending on the orientation of the corresponding plasmon oscillations in Ag NPs relative to the laser light polarization, permanent spectral holes of different strengths were burnt in the inhomogeneously broadened plasmon band. When probed with the light polarized parallel to the laser light polarization, the spectral hole appears to be much deeper as compared to the spectral hole, probed with the cross-polarized light, thus producing considerable LD in an initially isotropic ensemble of metal NPs. At the laser fluence of 17 mJ/cm², we achieve an LD magnitude of 20%. By focusing the linearly polarized laser light on the surface with Ag NPs and rotating its polarization in the course of scanning, one can impart arbitrary complicated patterns of LD to the Ag metasurface. Such a pattern may be readily recognized but difficult to reproduce, making it a promising earmark applicable in the fight against counterfeiting.