Linear and nonlinear optical properties of silicate oxide glasses containing metallic gold and silver nanoparticles

Glasses with metallic nanoparticles (NPs) are of great interest in photonics and plasmonics due to their unique linear and non-linear optical properties. These features directly arise from the localized surface plasmon... [ view full abstract ]

Glasses with metallic nanoparticles (NPs) are of great interest in photonics and plasmonics due to their unique linear and non-linear optical properties. These features directly arise from the localized surface plasmon resonance (LSPR) and the enhancement of the electric field in the vicinity of such nanoparticles.

We report on the embedded gold and silver nanoparticles in a standard silicate oxide glass. Au or Ag metallic compounds were introduced in vitreous oxide matrices as gold chloride (AuCl) or silver nitride (AgNO₃), respectively, together with some reducing agents in case of Au. The amorphous glass (Fig.1a) was obtained using the standard melt-quenching technique while metallic Au or Ag NPs were precipitated by thermal annealing of as-prepared glass plates in reducing atmosphere or in air (Fig.1b). Measurements of the absorbance spectra of the prepared samples in the UV-VIS range revealed the existence of the LSPR at expected wavelengths of 420 nm and 540 nm for Ag and Au NPs (Fig.1c), respectively. Moreover, the modeling of these spectra, using the Drude model, the Mie theory as well as the Maxwell-Garnet theory of the effective medium, allowed to determine the size (on the order of several nm) and the filling factor (on the order of 10^-5) of embedded NPs. Further proofs are given by analysis of TEM micrographs. The non-linear optical properties of samples, originating from the optical Kerr effect and multiphoton absorption, were investigated with the Z-scan method (Fig.2a) using the 35 fs laser pulses at 813 nm which were generated by a mode-locked Ti:sapphire laser system at a repetition rate of 1 kHz. The open (Fig.2b) and closed aperture (Fig.2d) z-scan curves for the as-annealed glass with dispersed Au nanoparticles were fitted with the standard Z-scan theory and the nonlinear absorption β and refractive index n₂ coefficients are determined. The measured nonlinear absorption and nonlinear phase shift for different energy of the incident laser pulse are shown in Fig.2c,e. Our studies clearly show the increase in the non-linearities in comparison to the samples without metallic NPs.