Multiply ionized carbon plasmas with index of refraction greater than one
Date
2007
Authors
Johnson, W. R., author
Dunn, J., author
Nilsen, J., author
Rocca, Jorge J., author
Marconi, M. C., author
Purvis, M., author
Grave, J., author
Filevich, J., author
Cambridge University Press, publisher
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Abstract
For decades the analysis of interferometry have relied on the approximation that the index of refraction in plasmas is due solely to the free electrons. This general assumption makes the index of refraction always less than one. However, recent soft x-ray laser interferometry experiments with Aluminum plasmas at wavelengths of 14.7 nm and 13.9 nm have shown fringes that bend the opposite direction than would be expected when using that approximation. Analysis of the data demonstrated that this effect is due to bound electrons that contribute significantly to the index of refraction of multiply ionized plasmas, and that this should be encountered in other plasmas at different wavelengths. Recent studies of Silver and Tin plasmas using a 46.9 nm probe beam generated by a Ne-like Ar capillary discharge soft-ray laser identified plasmas with an index of refraction greater than one, as was predicted by computer calculations. In this paper we present new interferometric results obtained with Carbon plasmas at 46.9 nm probe wavelength that clearly show plasma regions with an index of refraction greater than one. Computations suggest that in this case the phenomenon is due to the dominant contribution of bound electrons from doubly ionized carbon ions to the index of refraction. The results reaffirm that bound electrons can strongly influence the index of refraction of numerous plasmas over a broad range of soft x-ray wavelengths.
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Subject
soft x-ray laser
anomalous index of refraction
interferometry