Characterization of laser-produced plasmas for extreme ultraviolet and soft x-ray sources

The wide range of applications of extreme ultraviolet (EUV) and softX-ray sources including for next generation photolithography around 13.5 nm and 6.7 nm as well as for broadband EUV sources lead to the investigations of various methods to generate the radiation. In this thesis, spectral emission from laser-produced plasmas (LPPs) of several target materials such as tin, tin-gold alloy, tin-lead alloy, galinstan and gadolinium for EUV sources has been theoretically and experimentally characterized. LPPs of pure tin targets show very bright EUV emission around 13.5 nm whereas LPPs of Gd targets show unresolved transition arrays (UTAs) near 6.7 nm. Alloy targets such asSn-Au, Sn-Pb and galinstan give rise to a broadband EUV emission in the 10 - 18 nm regions, though the most intense radiation remains observed around 13.5 nm. The temporal behavior of Sn, Sn-Au and Sn-Pb alloys as well as Gd closely matches the temporal profile of the Nd:YAG laser used in the experiments.This thesis is divided into 9 Chapters. The theoretical background andmotivations of this PhD work are presented in Chapter 1, whereas theexperimental apparatus is described in Chapter 2. Chapter 3 discusses the theoretical calculations of the EUV and soft X-ray emission from several atomic elements including tin (Sn), gold (Au), lead (Pb), gallium (Ga), indium (In) as well as gadolinium (Gd) using the Cowan codes. Various steady state plasma calculations performed using the Colombant and Tonon model are also presented in Chapter 3. Spectral analysis of EUV emission from laser produced plasmas (LPPs) of Sn, Au and Sn-Au along with their conversion efficiencies (CEs) are compared in Chapter 4, whereas a galinstan LPP is highlighted in Chapter 5 as a promising EUV source around 13.5 nm based on its spectral behaviour at different laser fluxes and spot sizes. In the lastthree results and discussion chapters (Chapters 6-8), the temporal evolution of several material targets including Sn, Sn-Au, Sn-Pb and gadolinium is presented. Eventually Chapter 9 concludes the whole work.