Simulation of efficient extreme ultraviolet light generation from a 4-μm-wavelength laser irradiating pre-formed targets

Optimizing extreme ultraviolet (EUV) conversion efficiency (CE) is a core yet challenging requirement for laser-produced plasma sources. This study demonstrates the specific effects of laser- and tin target conditions on hydrodynamic and radiation properties of the light source, leading to a laser–target co-optimization scheme toward achieving optimal CE. For laser–droplet interactions, peak CE at 4-μm laser wavelength stems from modified laser penetration depth and balanced in-band radiation emissivity and opacity. However, geometric losses and strong reflections of laser energy prevent global CE optimization. The rarefied and spatially extended target induced by the pre-pulse can expand the laser–target interaction region and enhance laser absorption, leading to a substantial improvement in CE. Moreover, shaped-target morphology critically modulates laser ablation dynamics and in-band radiation. Symmetric and uniform optimized targets can be achieved by adjusting the delay time of the dual-pulse, which can mitigate the in-band radiation emission anisotropy. Eventually, it is found that the stable and homogeneous heating of optimized targets can maximize the CE to 7.1% under 4-μm laser irradiation. This study demonstrates a promising approach to improve the light performance through mid-infrared laser driving and target morphology selection.