Ho:LuAG single crystal fiber: growth, spectroscopy and laser characteristics

Lutetium aluminum garnet single-crystal fiber (SCF, ∼ Φ 0.9 mm - 165 mm) doped with 0.5 at.% Ho³⁺ has been grown by the micro-pulling-down (µ-PD) technique. The room-temperature absorption and emission spectra exhibit similar features to the bulk crystal. Laser performances of the SCFs with two different pump configurations, i.e., pump guiding and free-space propagation, are studied by employing a 1.9-µm laser diode and a high-brightness fiber laser, respectively. Laser slope efficiencies obtained with both pump configurations can be higher than 50%, and a maximum output power of 6.01 W is achieved at ∼ 2.09 µm with the former pump. The comparable efficiency to the high-brightness pump is an indication of that high laser performance can also be expected through pump-guiding in the SCF even with a low pump beam quality.