Growth, spectroscopy, and ∼3 μm continuous-wave laser oscillation of Ho,Pr:YGG crystal

Mid-infrared lasers at 3 μm hold many important applications in biological tissue ablation, gas detection, and so on. At present, holmium ion (Ho³⁺) can achieve efficient laser oscillation at this wavelength by the ⁵I₆→⁵I₇ transition. However, in the traditional high-phonon-energy oxide crystals (e.g., YAG), it is quite difficult to realize ∼3 μm continuous-wave (CW) lasing owing to the strong non-radiative relaxation and inherent self-terminating effect. Here, for the first time, we investigated the growth, spectroscopy, and mid-infrared lasing properties of Ho,Pr:YGG crystal. The growth of high-quality laser crystals was achieved using the optical floating zone method. Compared to the YAG host, YGG has a reduced phonon energy, which is beneficial for decreasing the probability of non-radiative relaxation and strengthening the ∼3 μm emission intensity. Then, Pr³⁺ ions were introduced as deactivators to reduce the lifetimes of ⁵I₇ low-level and promote the population inversion of Ho³⁺ activators. As a result, Ho,Pr:YGG yields the stable ∼3 μm CW lasing, delivering a maximum output power of 548 mW and a slope efficiency of 5.88%. As far as we are aware, this is the highest reported CW output at ∼3 μm among Ho³⁺-doped oxide-based laser crystals.