Delay optimisation of Gradient-Doped Nd: YAG laser ceramics via active mixing of Direct ink writing

• The delay optimisation strategy greatly reduces the delay distance by about 20.6 % for the change in volume of the mixing area and 29.0 % − 66.7 % for the change in component switching mode. • Gradient-doped transparent ceramics prepared using the optimised approach obtained a slope efficiency of 67.3%. • Delayed optimisation enables closer alignment of the compositional distribution in the sample to the designed gradient profile. Gradient doping of Nd: YAG (Nd: Y 3 Al 5 O 12 ) can relieve thermal effect during laser operation in solid-state lasers. Direct ink writing (DIW) is an effective method for fabricating gradient-doped structures. However, the delay issue during component switching significantly affects rare-earth ion concentration distribution in the samples, which includes delivery delay and transitional delay. They were respectively optimised by reducing the volume of mixing zone and by modifying component switching mode. Firstly, simulations of the mixing zone before and after optimisation were conducted using ANSYS Fluent to demonstrate the mixing uniformity. Secondly, the processes of component changes during extrusion were simulated to demonstrate the effectiveness of the two delay optimisation methods. Line patterns were printed using DIW with varying mixing zone volumes and component switching modes. The delay optimisation methods were confirmed to significantly reduce the impact of the delay by measuring Nd 3+ ion concentration. Furthermore, a mathematical model was developed to assess the influence of two delay optimisation methods on the delay. Finally, 0–0.5–1–0 at% Nd: YAG gradient-doped laser ceramics were successfully fabricated based on the proposed delay optimisation method, and the performance characterization of the Nd: YAG laser ceramics confirmed the efficacy of the method.