Estimation of the fs laser spot temperature inside TeO2–ZnO–Nb2O5 glass by using up-conversion green fluorescence of Er3+ ions

Laser heating of tellurite (TeO2)-based glass up to ∼550 K by femtosecond (fs) pulses of 800 nm from a regenerative Ti:sapphire laser was optically in situ monitored using green up-conversion fluorescence of Er3+ ions doped in TeO2-based glasses, where a fluorescence intensity ratio of two green up-conversion fluorescence at 526 nm (2H11/2–4I15/2) and 548 nm (4S3/2–4I15/2) was varied by thermal activation between 2H11/2 and 4S3/2 levels. By comparison with results on an aluminosilicate glass doped with Er3+, it was clearly found that the fs laser heating was caused by nonlinear absorption of the host material of TeO2-based glass via the imaginary part of the third-order nonlinear susceptibility (χ(3)).