High-Q lasing in Nd³⁺-doped phosphate glass microsphere resonators

Nd³⁺-doped glasses are the most widely used laser gain media. However, Nd³⁺-doped non-silica microsphere lasers generally have lower quality (Q) factors due to the presence of non-radiative energy-loss impurities in traditional glass systems. In this work, we report the first, to the best of our knowledge, Nd³⁺-doped phosphate glass microsphere laser with the highest Q-factor of 1.54 × 10⁶ among all Nd³⁺-doped non-silica glass microsphere lasers. Whispering gallery modes in the 1020-1120-nm band can be obtained for a typical microsphere with a diameter of 82.57 µm. When the pump power exceeds the threshold of 0.17 mW, single- and multi-mode microsphere lasing can be generated under 808-nm laser diode (LD) pumping. Typical Q-factors of the phosphate glass microspheres can reach 10⁶, which is at least an order of magnitude higher than those of other Nd³⁺-doped non-silica glass microsphere lasers. The Nd³⁺-doped phosphate glass microsphere laser reported in this work can be considered as an active optical/photonic device with low pump thresholds.