Femtosecond laser irradiation in Er3+ doped tellurite-phosphate glass for waveguide applications

This study investigates the feasibility of inducing crystallization in tellurite-phosphate glass within the TeO2-P2O5-BaF2-ZnF2-Na2O-Er2O3 system by direct laser writing (DLW) technique using a femtosecond laser beam operating at 1030 nm with a pulse duration of 230 fs. Two irradiation modes were examined: stationary-mode (1 MHz repetition rate, 160 nJ pulse energy, 120 s exposure time, for dot patterning) and translational-mode (200 kHz repetition rate, 10 mu m/s translation speed, 470 nJ pulse energy, for line patterning) of laser irradiation. Our results, validated by Raman spectroscopy and scanning electron microscopy, revealed the formation of barium fluoride and zinc barium phosphate crystals in the areas irradiated employing stationary-mode. However, only barium fluoride nanocrystals were detected in the lines induced by the fs-laser employing the translational-mode. SEM analysis of the morphology and size of the laser-induced crystals showcased intriguing findings. In stationary-mode, barium fluoride crystals were distributed across the entire dot pattern area (30 mu m), while zinc barium phosphate crystals were predominantly located at the edges of the dot spheres (with a size of 10 mu m). Interestingly, barium fluoride nanocrystals with a size below 100 nm were detected in the area of laser irradiation in translational mode. Further structural analysis revealed alterations in the tellurite (TeO4) and phosphate (Q(0)) structural units within the glass matrix of the fs-laser crystallized tellurite-phosphate system. Moreover, we discussed the changes in erbium emission across the UV-NIR region in both laser-induced crystals and the parent glass. Notably, a stronger emission of erbium ions was observed in the glass compared to the crystalline phases, which needs further investigations. These preliminary findings underscore the potential of fs-laser writing for the development of tellurite-phosphate glass-ceramics.