Ultrafast third-order optical nonlinearities of heavy metal oxide glasses containing gold nanoparticles

• Nonlinear optical effects were investigated in GeO2–Bi2O3 glasses with and without Au nanoparticles.
• Nonlinear refractive index spectra were measured from 480 to 1500 nm.
• The nonlinear refractive index is a ultrafast electronic process in this sample.
• Saturable absorption was observed within the plasmon band.

This work reports on the third-order nonlinear properties and the response time of GeO2–Bi2O3 glass, as well as the effect of gold nanoparticles on these properties. The nonlinear refractive index spectrum and the nonlinear absorption coefficient were determined by the Z-scan technique, and the response time was obtained through Kerr gate measurements, using femtosecond pulses. The results show that the presence of gold nanoparticles causes a saturable absorption effect that is overcome by the two-photon absorption process at higher light intensities, for wavelengths within the plasmon band. We measured a constant value for the nonlinear refractive index (n2) for the visible and infrared regions, which was not affected by the presence of gold nanoparticles in the sample. However, the n2 value is one order of magnitude higher than the one for fused silica and 1.5 times better than PGO (PbO–GeO2) glasses. In addition, the response time of the induced birefringence for the samples with and without gold nanoparticles is faster than the pulse duration (220 fs), indicating an ultra-fast electronic process.