Laser prepulse-induced deformation dynamics in tin microdroplets for extreme ultraviolet light source applications

This paper presents a detailed numerical investigation of the deformation dynamics of spherical tin (Sn) microdroplets under the action of laser prepulses, which is an essential process for optimizing extreme ultraviolet (EUV) lithography targets. A hybrid simulation method is developed, combining a single-fluid radiation hydrodynamics model for laser-produced plasmas with a two-phase flow model that incorporates surface tension effects. Two distinct scenarios are analyzed using this hybrid approach: nanosecond and picosecond prepulses, each characterized by markedly different energy deposition and deformation mechanisms. The simulations capture the full deformation process from initial laser impact to the capillary timescale, reproducing target morphologies that show good agreement with experimental observations. Detailed quantitative analyses of droplet expansion rates and geometries are also provided. Finally, the impact of the predeformed targets on EUV emission performance is evaluated by simulating the interaction of a <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mi mathvariant="normal">C</a:mi> <a:msub> <a:mi mathvariant="normal">O</a:mi> <a:mn>2</a:mn> </a:msub> </a:mrow> </a:math> main pulse with the deformed structures. This study offers significant insights into laser-droplet interactions and contributes to the development of precise control strategies for optimizing EUV target shaping.