Mechanisms of nonlinear optical absorption in (GeO2)1-x–(PbF2)x (0.1 ≤ x ≤ 0.3) modified germanate glasses

The structural, optical, and nonlinear absorption properties of (GeO2)1-x–(PbF2)x (0.1 ≤ x ≤ 0.3) glasses synthesized by conventional melting and quenching technique were investigated. Bandgap energies and Urbach energies were calculated by evaluating the linear absorption spectra. The increase in the PbF2 content resulted in 0.51 eV increase in bandgap energy and 0.28 eV decrease in Urbach energy. Z-scan experiment were performed to investigate nonlinear absorption properties, and a theoretical model including the contribution of one photon absorption, two photon absorption, excited state absorption, and saturable absorption to nonlinear absorption was considered in the evaluation of the experimental data. Although the highest effective nonlinear absorption coefficient was found with the highest PbF2 content due to the smallest bandgap energy, the highest downtrend in effective nonlinear absorption coefficients was also found for highest PbF2 content due to the smallest Urbach energy.