Recombination mode of extreme ultraviolet radiation in a lithium laser-produced plasma

This work provides new insights into the emission mechanisms of laser-produced lithium plasma in the extreme ultraviolet (EUV) spectral region, with important implications for the development of EUV light sources. High-resolution spectra of the Li III Lyman series were recorded using a custom-built grazing-incidence spectrometer. The analysis of relative line intensities and profiles allowed us to determine key plasma parameters, including the electron density and temperature of the radiating region. Contrary to the conventional understanding that EUV emission primarily originates from high-density, collisionally dominated plasma regions, we demonstrate that the dominant EUV power flux can arise from a recombination-dominated mechanism occurring in a low-density peripheral zone, far from the plasma core. This conclusion is supported by spatially and spectrally resolved imaging of the EUV-emitting plasma, obtained with a Schwarzschild objective, as well as by simulations performed with the RZ-Line code.