title: Prediction and observation of tin and silver plasmas with index of refraction greater than one in the soft x-ray range.
abstract: We present the calculated prediction and the experimental confirmation that doubly ionized Ag and Sn plasmas can have an index of refraction greater than one for soft x-ray wavelengths. Interferometry experiments conducted using a capillary discharge soft x-ray laser operating at a wavelength of confirm that in few times ionized laser-created plasmas of these elements the anomalous dispersion from bound electrons can dominate the free electron contribution, making the index of refraction greater than one. The results confirm that bound electrons can strongly influence the index of refraction of numerous plasmas over a broad range of soft x-ray wavelengths confirming recent observations. The understanding of index of refraction at short wavelengths will become even more essential during the next decade as x-ray free electron lasers will become available to probe a wider variety of plasmas at higher densities and shorter wavelengths.
authors.affiliation: Department of Physics, National Science Foundation ERC for Extreme Ultraviolet Science and Technology, Colorado State University, Fort Collins, CO 80523, USA.
authors.forename: Jorge
authors.initials: J
authors.lastname: Filevich
authors.forename: Jonathan
authors.initials: J
authors.lastname: Grava
authors.forename: Mike
authors.initials: M
authors.lastname: Purvis
authors.forename: Mario C
authors.initials: MC
authors.lastname: Marconi
authors.forename: Jorge J
authors.initials: JJ
authors.lastname: Rocca
authors.forename: Joseph
authors.initials: J
authors.lastname: Nilsen
authors.forename: James
authors.initials: J
authors.lastname: Dunn
authors.forename: Walter R
authors.initials: WR
authors.lastname: Johnson