Analysis And Simulations Of XUV/EUV Spectra Of Laser-produced Sn, I And Au Plasma

Laser-produce plasmas(LPP),formed by focusing a beam from a pulsed laser onto solid sample targets,can emit an intense burst of radiation over a broad spectral range, making them ideally suited to spectroscopic studies.The spectra generally consist of lines and continuum,depending on factors such as the laser power density and the material used.Therefore,laser-produced plasma spectroscopy(LPPs) has been established as a versatile tool for atomic physics studies in the IR to X-ray regions because of its features, such as simplified production and operation,broad emission,high shot to shot intensity, short pulse duration,good reproducibility,lower costs and so on.Using LPPs,one can obtain lots of information about the atomic structure and related dynamics processes.The work reported in this thesis consists of the investigation of laser-produced plasma as EUV lithography sources and inner-shell photoabsorption studies of laser-produced iodine and gold plasmas.The following studies focus mainly on the theoretical analysis and simulations of spectra mentioned above.Laser-produced plasmas are considered to be important candidate sources of extreme ultraviolet(EUV) radiation for application in future lithography tools for the high-volume manufacturing of computer chips.In this work,extreme ultraviolet(EUV) emission spectra from laser-produced Sn plasmas have been experimentally investigated at different power densities in the 9.5-18 nm wavelength range.Experimental results indicate the presence of a broad reabsorption band and some pronounced dips because of opacity effects in the spectra.With increasing power densities,the reabsorption band shifts to the shorter wavelength side and the absorption dips become deeper.Theoretical calculations using the Cowan code show that the dips arise from the 4d-4f and 4p-4d transitions.Using detailed configuration accounting(DCA) with the term structures treated by the unresolved transition array(UTA) model,we analyze the opacity effects and simulate the spectra.By comparing the results of the simulations with experiments,it can be concluded that the plasma from a 5%Sn target gives essentially pure emission,while the spectra from a pure Sn target contains both emission and absorption,with electron temperatures ranging from 28 to 15 eV,and electron densities from 5.0×10²⁰ to 3.7×10¹⁹ cm^-3,in going from the core to the outer plasma region.The 4d photoabsorption spectra of I²⁺,I³⁺ and I⁴⁺ have been obtained in the 70-127 eV region with the dual laser produced plasma technique at time delays ranging from 400 to 520 ns.With decreasing time delay,the dominant contribution to spectra evolves from I²⁺ to I⁴⁺ ions,and each spectrum contains discrete 4d-nf transitions and a broad 4d-εf shape resonance,which are identified with the aid of multiconfiguration Hartree- Fock calculations.The excited states decay by direct autoionization involving 5s or 5p electrons and rates fbr the different processes and resulting linewidths were calculated. With increasing ion stage,the 4d-εf shape resonance becomes intense and broader in going from I²⁺ to I³⁺,and then vanishes in I⁵⁺.In addition,the discrete structure of the calculated spectrum of each ion gradually approaches the corresponding shape resonance position.Based on the assumption of a normalized Boltzmann distribution amongst the excited states and a steady-state collisional-radiative(CR) model,we reproduced spectra which are in good agreement with experiment.The photoabsorption processes of Au²⁺,Au³⁺,and Au⁴⁺ have been investigated experimentally and theoretically in the 70-127 eV region.Using the dual laser-produced plasma(DLP) technique,the 4f and 5p photoabsorption spectrum has been recorded at 50 ns time delay and was found to be dominated by a great number of transition lines from 4f-5d,6d and 5p-5d,6s transitions,which have been identified by comparison with the aid of Hartree-Fock with configuration interaction calculations.The characteristic feature of the spectrum is that satellite lines from excited configurations containing one or two 6s electrons are more important than resonance lines,and with increasing ionization,satellite contributions from states with one 6s spectator electron gradually become more important than those with two 6s spectator electrons.Based on the assumption of a normalized Boltzmann distribution among the excited states and a steady state collisional-radiative model, we succeeded in reproducing a spectrum which is in good agreement with experiment.In a word,the main goals of the work presented in this thesis can be helpful to the further development of optical diagnostic methods fbr application to EUV producing discharges,and improving the understanding of the physical properties of these laser-produced plasmas.