Plasma interferometry and how the bound electron contribution can bend fringes in unexpected ways

Nilsen, J; Johnson, W R

doi:10.1364/AO.44.007295

Plasma interferometry and how the bound electron contribution can bend fringes in unexpected ways

Journal Article · Fri Feb 11 04:00:00 EST 2005 · Applied Optics

DOI:https://doi.org/10.1364/AO.44.007295· OSTI ID:875924

Nilsen, J; Johnson, W R

For decades the measurement of the electron density in plasmas by interferometers has relied on the approximation that the index of refraction in a plasma is due solely to the free electrons and therefore is less than one. Recent measurements of Al plasmas using X-ray laser interferometers have observed anomalous results with the fringes bending the opposite way than expected due to the index of refraction being larger than one. Subsequent analysis showed that the bound electrons have a larger contribution to the index of refraction with the opposite sign than the free electrons. This effect extends far from the absorption edges and lines of the bound electrons. Utilizing a new average atom code we calculate the index of refraction in C, Al, Ti and Pd plasmas and show that there are many conditions over which the bound electron contribution dominates as we explore photon energies from the optical to 100 eV (12 nm) soft X-rays. During the next decade X-ray free electron lasers and other sources will be available 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.

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Research Organization:: Lawrence Livermore National Laboratory (LLNL), Livermore, CA

Sponsoring Organization:: USDOE

DOE Contract Number:: W-7405-ENG-48

OSTI ID:: 875924

Report Number(s):: UCRL-JRNL-209655

Journal Information:: Applied Optics, Journal Name: Applied Optics Journal Issue: 34 Vol. 44; ISSN 0003-6935; ISSN APOPAI

Country of Publication:: United States

Language:: English

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