Advanced numerical modeling of light-matter interactions at nanometer length scales*

Scattering-type, scanning near-field infrared microscopy (S-SNIM) is a cutting-edge experimental technique that allows infrared spectra to be obtained at nanometer scale spatial resolution well beyond the diffraction limit of light. Effective extraction of meaningful information from experimental data relies on accurate modeling of the light-probe-sample interaction. This is especially true in media with more intricate geometries and optical properties such as thin films, nanostructures, and anisotropic materials because analytical models are inadequate for these systems. Here we demonstrate advanced, fully numerical methods to simulate the near-field infrared response of different systems and compare directly with experimental data. We will present spectra of thin films (e.g. SiO₂ films on Si substrates and surface metallicity of SrTiO₃), spectra and imaging of nanostructures (e.g. nano-platelets of Cu₂S), and the near-field infrared response of materials with anisotropic dielectric function (e.g. rutile TiO₂). This work demonstrates fully numerical simulations as a universal and reliable way forward for modeling of experimental S-SNIM spectra from a diverse range of systems.