Low-threshold whispering-gallery-mode microlasers fabricated in a Nd:glass substrate by three-dimensional femtosecond laser micromachining

We report on fabrication of whispering-gallery-mode microlasers in a Nd:glass chip by femtosecond laser three-dimensional micromachining. The main fabrication procedures include the fabrication of freestanding microdisks supported by thin pillars by femtosecond laser ablation of the glass substrate immersed in water, followed by CO₂ laser annealing for surface smoothing. The quality (Q) factor of the fabricated microcavity is measured to be 1.065 × 10⁶. Lasing is observed at a pump threshold as low as ∼69 μW at room temperature with a continuous-wave laser diode operating at 780 nm. This technique allows for fabrication of microcavities of high Q factors in various dielectric materials, such as glasses and crystals.