Optical detection of near infrared femtosecond laser-heating of Er3+-doped ZnO–Nb2O5–TeO2 glass by green up-conversion fluorescence of Er3+ ions

The green up-conversion fluorescence of Er3+ ions doped in an nonlinear optical ZnO–Nb2O5–TeO2 glass was observed by using 800 nm excitation from a regenerative femtosecond (fs) Ti:Sapphire laser. The detailed analysis on two fluorescence lines at 526 nm (2H11/2–4I15/2) and 548 nm (4S3/2–4I15/2) revealed the fs laser heating of the multi-component TeO2-based glass, which was possibly due to its nonlinear absorption of the host glass via the imaginary part of the third-order optical susceptibility (χ(3)). The result was compared with that of a Er3+-doped aluminosilicate glass under the same irradiation condition. When the fs laser was irradiated to the multicomponent TeO2-based glass in the power density of 150 TW/cm2, the laser spot was heated up to ∼520 K, which however was still less than the glass transition temperature (Tg=688 K). This technique provides a useful sensing method of laser spot temperature even inside transparent materials.