Spatially resolved extreme ultraviolet emission and opacity effects in laser-produced zinc plasmas

Laser-produced plasmas (LPPs) exhibit pronounced spatial nonuniformity and transient evolution, which strongly influence the generation and transport of extreme-ultraviolet (EUV) radiation. In this study, the EUV emission characteristics of LPPs of zinc (Zn) in the 8-15 nm wavelength range were systematically investigated by combining spatially resolved spectroscopic measurements, atomic structure calculations, radiation-hydrodynamic simulations, and three-dimensional spectral modeling. The experimental spectra exhibit strong broadband emission in the 12-15 nm region. Atomic structure calculations for Zn⁶⁺-Zn⁹⁺ show that the main spectral features arise from overlapping 3p-3d and 3d-mf transition arrays. Configuration interaction significantly redistributes the oscillator strengths and modifies the spectral profiles, while the contribution from doubly excited configurations is substantially weaker than that from singly excited configurations. RHDLPP simulations reveal pronounced spatiotemporal gradients in plasma temperature and density during plasma expansion. By further coupling the hydrodynamic results with the SpeIma3D model and accounting for the actual observation geometry and temporal integration, the main spatial evolution and spectral structures observed experimentally are reproduced. Radiative-transfer calculations show that self-absorption is strongest in the dense near-target region and gradually weakens as plasma expands. Additionally, the wavelength- and direction-dependent optical thickness gives rise to pronounced angular anisotropy in the emergent EUV radiation. These results reveal the intrinsic relationship among atomic transitions, plasma evolution, and radiative transport, providing a basis for understanding the formation mechanism of broadband short-wavelength EUV emission.