Investigation on the charge-state distribution diagnosis oflaser-produced Al plasmas

Abstract

Laser-produced plasmas (LPP) have been known to possess great application potential under extreme ultraviolet (EUV) lithography, soft X-ray micrography, and heavy ion accelerator, highly charged ion optical frequency standards, pulsed laser deposition, astrophysics and nuclear fusion. The applications in these fields require a clearer understanding of the evolutionary behavior of the LPP. However, LPP is neither homogeneous nor static during their expanding and cooling process, which involves complex physical processes. For a deep understanding of the LPP, many diagnostic methods and techniques have been developed, such as spectroscopy, fast imaging, time-of-flight (TOF), laser interferometry and Thomson scattering. Among these methods, spectroscopy has been the most widely used diagnostic method, which can be used to obtain relatively more state information. However, the diagnosis results of charge-state distribution obtained by spatio-temporally resolved spectroscopy are local and transient, and cannot therefore obtain the overall distribution. In order to have a more comprehensive understanding of charge-state distribution and its evolutionary behavior of the LPP, other diagnostic methods are needed. The TOF method is used for the measurement of highly charged ions of the LPP, which can be used to obtain the overall charge-state distribution information. Therefore, in this work, spectrometry and TOF method were used for the diagnosis of charge-state distribution of the LPP in a vacuum. The EUV emission spectra of laser-produced Al plasmas were measured by using spatio-temporally resolved laser-produced plasmas spectroscopy technique. The charge-state distributions with different delay times at the distance of 2.0 mm from target surface were diagnosed by spectral simulation and their evolution behavior were also analyzed. The TOF spectra of laser-produced Al plasmas were measured by the TOF method, and the overall charge-state distribution of ions in laser-produced Al plasmas was obtained. The results revealed that spectroscopy can diagnose the local and transient charge-state distribution of ions in the laser-produced plasmas, and the TOF method can be used to diagnose its overall distribution, and the two diagnostic methods therefore complement each other. This work aims to clarify the complementarity of the two methods, and to provide a method support for the comprehensive and accurate understanding of the charge-state distribution and evolution evolutionary behavior during the expansion process of the LPP, and also provides a reference for further optimization and modification of the radiation hydrodynamics model of the LPP.