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Browsing by Author "Filevich, Jorge, author"

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    Application of extremely compact capillary discharge soft x-ray lasers to dense plasma diagnostics
    (Colorado State University. Libraries, 2003) Rocca, Jorge, J., author; Hammarsten, E. C., author; Jankowska, E., author; Filevich, Jorge, author; Marconi, Mario Carlos, author; Moon, Stephen J., author; Shlyaptsev, Vyacheslav N., author; American Institute of Physics, publisher
    Table-top capillary discharge soft x-ray lasers combine the advantages of a small size and a high repetition rate with an extremely high brightness similar to that of their laboratory-size predecessors. When utilized to probe high density plasmas their short wavelength results in a higher critical density, reduced refraction, decreased free-electron absorption, and higher resolution as compared to optical probes. These characteristics allow the design of experiments capable of measuring the evolution of plasmas with density-scale length products that are outside the reach of optical lasers. This paper reviews the use of a 46.9 nm wavelength Ne-like Ar capillary discharge table-top laser in dense plasma diagnostics, and reports soft x-ray laser interferometry results of spot-focus Nd:YAG laser plasmas created at moderate irradiation intensity (~7×1012 W cm-2) with ; ~13 ns pulse width duration laser pulses. The measurements produced electron density maps with densities up to 0.9×1021 cm-3 that show the development of a concave electron density profile that differ significantly from those of a classical expansion. This two-dimensional behavior, that was recently also observed in line-focus plasmas, is analyzed here for the case of spot-focus plasmas with the assistance of hydrodynamic model simulations. The results demonstrate the use of a table-top soft x-ray laser interferometer as a new high resolution tool for the study of high density plasma phenomena and the validation of hydrodynamic codes.
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    Observation of multiply ionized plasmas with dominant bound electron contribution to the index of refraction
    (Colorado State University. Libraries, 2006) Shlyaptsev, Vyacheslav N., author; Hunter, James R., author; Keenan, Roisin, author; Smith, Raymond F., author; Dunn, James, author; Scofield, J. H., author; Nilsen, Joseph, author; Moon, Stephen J., author; Marconi, Mario Carlos, author; Rocca, Jorge, J., author; Filevich, Jorge, author; Elsevier Ltd., publisher
    We report anomalous fringe shifts observed in soft X-ray laser interferograms of laser-created Al plasmas. This clear experimental evidence shows that the contribution of bound electrons can dominate the index of refraction of laser-created plasmas at soft X-ray wavelengths, resulting in values greater than 1. The comparison of measured and simulated interferograms shows that this results from the dominant contribution of low-charge ions to the index of refraction. This usually neglected bound electron contribution can affect the propagation of soft X-ray radiation in plasmas and the interferometric diagnostics of plasmas for many elements.
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    Picosecond 14.7 nm interferometry of high intensity laser-produced plasmas
    (Colorado State University. Libraries, 2005) Marconi, Mario C., author; Ng, Andrew, author; Hunter, James R., author; Shlyaptsev, Vyacheslav N., author; Nilsen, Joseph, author; Keenan, Roisin, author; Rocca, Jorge J., author; Moon, Stephen J., author; Smith, Raymond F., author; Filevich, Jorge, author; Dunn, James, author; Cambridge University Press, publisher
    We have developed a compact, 14.7 nm, sub-5 ps X-ray laser source at Lawrence Livermore National Laboratory (LLNL) together with a Mach-Zehnder type diffraction grating interferometer built at Colorado State University for probing dense, high intensity laser-produced plasmas. The short wavelength and pulse length of the probe reduces refraction, absorption effects within the plasma and minimizes plasma motion blurring. This unique diagnostic capability gives precise two-dimensional (2D) density profile snapshots and is generating new data for rapidly evolving laser-heated plasmas. A review of the results from dense, mm-scale line focus plasma experiments will be described with detailed comparisons to hydrodynamic simulations.
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    Picosecond-resolution soft-x-ray laser plasma interferometry
    (Colorado State University. Libraries, 2004) Shlyaptsev, Vyacheslav N., author; Ng, Andrew, author; Nilsen, Joseph, author; Moon, Stephen J., author; Hunter, James R., author; Keenan, Roisin,, author; Dunn, James, author; Smith, Raymond F., author; Marconi, Mario C., author; Rocca, Jorge J., author; Filevich, Jorge, author; Optical Society of America, publisher
    We describe a soft-x-ray laser interferometry technique that allows two-dimensional diagnosis of plasma electron density with picosecond time resolution. It consists of the combination of a robust high-throughput amplitude-division interferometer and a 14.7-nm transient-inversion soft-x-ray laser that produces ~5-ps pulses. Because of its picosecond resolution and short-wavelength scalability, this technique has the potential for extending the high inherent precision of soft-x-ray laser interferometry to the study of very dense plasmas of significant fundamental and practical interest, such as those investigated for inertial confinement fusion. Results of its use in the diagnostics of dense large-scale laser created plasmas are presented.
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    Prediction and observation of tin and silver plasmas with index of refraction greater than one in the soft x-ray range
    (Colorado State University. Libraries, 2006) Johnson, Walter R., author; Dunn, James, author; Nilsen, Joseph, author; Rocca, Jorge J., author; Marconi, Mario C., author; Purvis, Mike, author; Grava, Jonathan, author; Filevich, Jorge, author; American Physical Society, publisher
    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 46.9 nm (26.44 eV) 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 abroad 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.
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    Refraction effects on x-ray and ultraviolet interferometric probing of laser-produced plasmas
    (Colorado State University. Libraries, 2003) Marconi, Mario C., author; Filevich, Jorge, author; Rocca, Jorge J., author; Shlyaptsev, Vyacheslav N., author; Hunter, James R., author; Nilsen, Joseph, author; Dunn, James, author; Smith, Raymond F., author; Optical Society of America, publisher
    We present a study detailing the effects of refraction on the analysis and interpretation of line-of-site optical probe characterization techniques within laser-produced plasmas. Results using x-ray laser backlit grid deflectometry and ray-tracing simulations illustrate the extent to which refraction can be a limiting factor in diagnosing high-density, short-scale-length plasmas. Analysis is applied to a recent experiment in which soft x-ray interferometry was used to measure the electron density within a fast-evolving Al plasma. Comparisons are drawn between extreme ultraviolet and ultraviolet probe wavelengths.
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    Soft x-ray laser interferometry of dense plasmas
    (Colorado State University. Libraries, 2007) Filevich, Jorge, author; Rocca, Jorge J. G., advisor
    This Dissertation presents the results of the study of plasmas using soft x-ray laser interferometry. The use of soft x-ray wavelengths (14.7 nm and 46.9 nm) permits probing plasmas that are denser and that have steeper density gradients than those that can be probed using optical interferometry. The use of diffraction gratings as beam splitters permitted the construction of a novel interferometer design that is robust, stable and with high throughput. The measurements conducted include the first demonstration of soft x-ray laser interferometry with picosecond resolution. The first set of results presented herein are the observation of an unexpected on-axis density depression in narrow-focus laser-created plasmas. It is caused by plasma-radiation-induced ablation of target material outside of the region irradiated by the plasma-heating laser. This colder material expands at a slower velocity than the hotter central region, resulting in the observed on-axis density depression. The effect is shown to be a general phenomenon, present in many narrow focus plasmas under different irradiation conditions. The second set of results unveiled the significant contribution of bound electrons to the index of refraction of multiply ionized plasmas. Experiments that mapped the density of aluminum plasmas using a λ=14.7 nm laser beam showed interference fringes that bent in the direction opposite to that expected, contradicting the widely accepted assumption that the index of refraction for multiply ionized plasmas at soft x-ray wavelengths only depends on the free electrons. The contribution of bound electrons to the index of refraction is shown to be significant, and to affect a broad range of wavelengths due to numerous bound-bound and bound-free transitions present in the plasma. Moreover, the contribution of bound electrons to the index of refraction was shown to be important in several materials at different probe soft x-ray wavelengths, in particular for tin, silver and carbon plasmas probed at λ=46.9 nm. This fundamental result affects not only the interpretation of soft x-ray interferograms for plasma density measurements, but also the propagation of soft x-ray light in plasmas in general.
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    Table-top soft X-ray laser interferograms of dense laser-created plasma
    (Colorado State University. Libraries, 2002) Jankowska, E., author; Hammarsten, E. C., author; Filevich, Jorge, author; Marconi, Mario Carlos, author; Rocca, Jorge J., author; IEEE, publisher
    We report soft X-ray interferograms that illustrate the use of a very compact table-top soft X-ray laser in mapping the electron density evolution of a dense plasma. The spatial density distribution of a point-focus laser-created plasma with ~300 μm dimension was measured for densities up to ~6.5 × 1020 cm-3.