Direct Ink Writing of Gradient‐Doped Yb:YAG Laser Ceramics From Slurry With Improved Printability

ABSTRACT

Direct ink writing (DIW) has been developed to be an important method for fabricating laser ceramics with a designed gain profile, which aims to address thermal management issues. However, how to prepare the slurry with both good flowability and shape retention was still a challenge. In this work, polyethyleneimine (PEI) was introduced as a flocculant to improve the printability of the DIW slurry. With the addition of 0.12 wt.% PEI‐5000, the storage modulus of the slurry was increased to G' = 14 800 Pa, three times as high as that of the slurry with hydroxyethyl cellulose (HEC). Meanwhile, the lower flow point ( τ _f = 108 Pa) was maintained, and the height‐to‐width ratio of the single filament printed by the selected slurry was 0.86. The slurry with PEI‐5000 exhibited good printability, showing a better balance between flowability and shape retention. Using the optimized slurry combined with active mixing, 0–2.5–5.0–2.5–0 at.% Yb:YAG gradient‐doped laser ceramics were successfully fabricated. The in‐line transmittance of the polished ceramics (5.6 mm thickness) was 82.5% at 1100 nm and 77.8% at 400 nm. By pumping with a fiber‐coupled diode laser, a maximum output power of 26.1 W was achieved, corresponding to a slope efficiency of 54%.