Emission and absorption in laser produced plasmas: Processes and applications

Abstract

Laser produced plasmas have been used for many years as intense sources of extreme ultraviolet (EUV) and soft x-ray radiation. Depending on the choice and composition of target the EUV spectra can be dominated by line, unresolved transition array (UTA) or continuum emission. Line and UTA emission have found application in various proposed EUV sources for lithography, which is based on the availability of mirrors with high reflectivity in a 2% bandwidth at a wavelength of 13.5 nm. The results of recent experimental measurements of absolute in-band and out of band intensity, ion distribution and debris are presented. It was found that because of opacity effects, the conversion efficiency is sensitive to ion density and laser wavelength. Various schemes to improve the conversion efficiency are discussed as are the results of recent plasma modelling calculations. In addition, laser produced plasmas of some high Z elements emit intense line free continua over extensive energy ranges. Some recent results on inner shell photoabsorption spectra of Sn, I and Au ions obtained using these continua are presented also. © 2009 IOP Publishing Ltd.