Optical properties and ultrafast optical nonlinearity of Yb³⁺ doped sodium borate and bismuthate glasses

In this paper, we report the optical and ultrafast nonlinear optical properties of Yb³⁺ doped sodium borate and bismuthate glasses. The glasses have been prepared through the melt quench technique. Optical absorption measurements show compositional dependent absorption spectrum of Yb ³⁺, which is due to the higher crystal field induced by Bi ³⁺ ions. Local structure of the glasses has been identified by using Fourier transform infrared and Raman studies. From open aperture z -scan measurements done by using 100 fs laser pulses, the ultrafast optical nonlinearity in these materials is calculated at the nonresonant excitation wavelength of 800 nm. The measured three-photon absorption originates from the glass host, with contributions from the nonbridging oxygens and the nonlinear electronic polarization of the Bi³⁺ ions.