A drop-on-demand generator for liquid metal toward extreme ultraviolet (EUV) applications

Laser-produced plasma (LPP) extreme-ultraviolet (EUV) sources require stable, small-diameter liquid-metal droplets. Here, we present a high-power drop-on-demand generator based on a co-fired multilayer stacked piezoelectric actuator and a three-dimensional (3D)-printed nozzle for liquid-metal target delivery. The actuator stores a nominal electrical energy of ∼625 µJ per pulse, enabling stable longitudinal actuation and ejection of gallium-indium-tin (GaInSn) droplets. High-speed stroboscopic visualization reveals that the meniscus response begins earlier than predicted by classical waveguide theories. A dual-acoustic-time model is therefore proposed, in which a fast solid-borne longitudinal wave contributes to the early meniscus motion. The device produces monodisperse droplets with a diameter of 36.2 ± 0.1 µm at frequencies up to 1.5 kHz with high spatial stability. In laser-droplet interaction tests, 3D-printed alumina (Al2O3) nozzles show greater resistance to plasma back-ablation than polymer nozzles after 3 × 105 laser pulses. These results demonstrate stable liquid-metal target delivery and improved nozzle resistance to plasma-induced damage, supporting the development of droplet generators for laboratory LPP EUV research.