Plasmonically Coupled Faraday Effect in Fe- and Au-doped Silicate Glasses Irradiated with Femtosecond Laser

The optical properties and the magneto-optical responses were space-selectively modified in transparent Fe3+ -and Au3+-doped glasses by irradiation with an infrared femtosecond laser and two-step annealing. The primary annealing at 450 degrees C induced the precipitation of magnetic spinel-typed Fe-oxide nanoparticles, and the precipitation of Au nanoparticles occurred during the secondary annealing at 550 degrees C. As a result, the irradiated and annealed glasses shows localized surface plasmon resonance absorption at around 510 nm, and also plasmonically coupled peaks at almost the same wavelength in Faraday rotation spectra. As increasing the pulse energy, the position of the localized surface plasmon resonance (LSPR) peak slightly shifted into the shorter wavelength, which is due to the decrease in the size of Au nanoparticles. The LSPR-coupled Faraday peaks were observed as a negatively enhanced rotation, which suggests that ferrimagnetic contribution to the magneto-optical properties was enhanced by the electric field on the surface of Au nanoparticles. This coupling phenomenon emerged as a result of a modification of composition of host glasses.