Abstract
The soft x-ray spectra of heavy element plasmas are frequently dominated by unresolved transition array (UTA) emission. We describe the spectral evolution of an intense UTA under optically thin conditions in platinum plasmas. The UTA was observed to have a peak wavelength around 4.6 nm at line-of-sight averaged electron temperatures less than 1.4 keV at electron densities of (2.5–7.5) × 1013 cm−3. The UTA spectral structure was due to emission from 4d–4f transitions in highly charged ions with average charge states of q = 20–40. A numerical simulation successfully reproduced the observed spectral behavior.
Highlights
The spectral behavior of unresolved transition array (UTA) emission in the soft x-ray (SXR) and extreme ultraviolet (EUV) spectral regions from highly charged ions (HCIs) in heavy element plasmas is of great interest in different fields of fundamental physics and applications, such as table-top plasma-based coherent EUV-SXR lasers[1] and incoherent plasma sources for generation semiconductor lithography.[2,3]
It is important to develop an efficient, high brightness light source in the carbon window SXR spectral region by optimization of the spectral emission from suitable HCI plasma, which can be coupled with wavelength matched SXR optical components, together with simplified benchmarking and modeling to understand the underlying physics
In order to achieve an efficient carbon window light source, we have shown that the spectral structure from highly charged Pt ions in plasmas lies in this region.[7]
Summary
The spectral behavior of unresolved transition array (UTA) emission in the soft x-ray (SXR) and extreme ultraviolet (EUV) spectral regions from highly charged ions (HCIs) in heavy element (high-Z) plasmas is of great interest in different fields of fundamental physics and applications, such as table-top plasma-based coherent EUV-SXR lasers[1] and incoherent plasma sources for generation semiconductor lithography.[2,3] This spectral region is important for material structure determination using techniques such as near-edge x-ray absorption fine-structure spectroscopy.[4].
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