Spectroscopic study of low-pressure microwave-induced helium discharge in the extreme ultraviolet wavelength range.

This article focuses on the study and optimization of a low-pressure microwave (MW)-induced helium discharge as a laboratory-based extreme ultraviolet (EUV) radiation source. Using spectroscopic measurements in the 12.5–60.0 nm wavelength range, the intensities of two strong helium emission lines at 30.38 nm and 58.43 nm were analyzed under varying discharge powers and pressures. Assuming a Maxwellian electron energy distribution and corona equilibrium for MW powers above 90 W and pressures above 1.19 mbar, the electron temperature was determined to range from 3.7 to 5.6 eV, and the electron density was found to be on the order of 10^10 cm^−3. The study identified optimal discharge pressures near 1.45–2.18 mbar for the 30.38 nm line and around 3.45 mbar for the 58.43 nm line, providing insights into the plasma behavior and conditions that maximize EUV emission intensity in this system.