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Proceedings Paper

Searching for plasmas with anomalous dispersion in the soft x-ray regime
Author(s): Joseph Nilsen; Walter R. Johnson; K. T. Cheng
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Paper Abstract

Over the last decade the electron density of plasmas has been measured using X-ray laser interferometers in the 14 to 47 nm wavelength regime. With the same formula used in decades of experiments with optical interferometers, the data analysis assumes the index of refraction is due only to the free electrons, which makes the index less than one. Over the last several years, interferometer experiments in C, Al, Ag, and Sn plasmas have observed plasmas with index of refraction greater than one at 14 or 47 nm and demonstrated unequivocally that the usual formula for calculating the index of refraction is not always valid as the contribution from bound electrons can dominate the free electrons in certain cases. In this paper we search for other materials with strong anomalous dispersion that could be used in X-ray laser interferometer experiments to help understand this phenomena. An average atom code is used to calculate the plasma properties. This paper discusses the calculations of anomalous dispersion in Ne and Na plasmas near 47 nm and Xe plasmas near 14 nm. With the advent of the FLASH X-ray free electron laser in Germany and the LCLS X-FEL coming online at Stanford in 2 years the average atom code will be an invaluable tool to explore plasmas at higher X-ray energy to identify potential experiments for the future. During the next decade X-ray free electron lasers and other X-ray sources will be used to probe a wider variety of plasmas at higher densities and shorter wavelengths so understanding the index of refraction in plasmas will be even more essential.

Paper Details

Date Published: 12 October 2007
PDF: 10 pages
Proc. SPIE 6702, Soft X-Ray Lasers and Applications VII, 67020N (12 October 2007); doi: 10.1117/12.732533
Show Author Affiliations
Joseph Nilsen, Lawrence Livermore National Lab. (United States)
Walter R. Johnson, Univ. of Notre Dame (United States)
K. T. Cheng, Lawrence Livermore National Lab. (United States)

Published in SPIE Proceedings Vol. 6702:
Soft X-Ray Lasers and Applications VII
Gregory J. Tallents; James Dunn, Editor(s)

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