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Creating and Probing Extreme States of Materials: From Gases and Clusters to Biosamples and Solids
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Molecular biophysics.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Free-electron lasers provide high intensity pulses with femtosecond duration and are ideal tools in the investigation of ultrafast processes in materials. Illumination of any material with such pulses creates extreme conditions that drive the sample far from equilibrium and rapidly convert it into high temperature plasma. The dynamics of this transition is not fully understood and the main goal of this thesis is to further our knowledge in this area.

We exposed a variety of materials to X-ray pulses of intensities from 1013 to above 1017 W/cm2. We found that the temporal evolution of the resulting plasmas depends strongly on the wavelength and pulse intensity, as well as on material related parameters, such as size, density, and composition.

In experiments on atomic and molecular clusters, we find that cluster size and sample composition influence the destruction pathway. In small clusters a rapid Coulomb explosion takes place while larger clusters undergo a hydrodynamic expansion. We have characterized this transition in methane clusters and discovered a strong isotope effect that promotes the acceleration of deuterium ions relative to hydrogen. Our results also show that ions escaping from exploding xenon clusters are accelerated to several keV energies.

Virus particles represent a transition between hetero-nuclear clusters and complex biological materials. We injected single mimivirus particles into the pulse train of an X-ray laser, and recorded coherent diffraction images simultaneously with the fragmentation patterns of the individual particles. We used these results to test theoretical damage models. Correlation between the diffraction patterns and sample fragmentation shows how damage develops after the intense pulse has left the sample.

Moving from sub-micron objects to bulk materials gave rise to new phenomena. Our experiments with high-intensity X-ray pulses on bulk, metallic samples show the development of a transient X-ray transparency. We also describe the saturation of photoabsorption during ablation of vanadium and niobium samples.

Photon science with extremely strong X-ray pulses is in its infancy today and will require much more effort to gain more knowledge. The work described in this thesis represents some of the first results in this area.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. , 66 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 975
Keyword [en]
free-electron laser, ultrashort X-rays, non-equilibrium plasma, Coulomb explosion, isotope effect, hydrodynamic expansion, ion acceleration, high intensity lasers, ablation, time-of-flight spectroscopy
National Category
Biophysics
Research subject
Physics
Identifiers
URN: urn:nbn:se:uu:diva-180997ISBN: 978-91-554-8477-4 (print)OAI: oai:DiVA.org:uu-180997DiVA: diva2:555998
Public defence
2012-11-09, A1:107, Biomedical Center (BMC), Husargatan 3, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2012-10-17 Created: 2012-09-14 Last updated: 2013-01-23Bibliographically approved
List of papers
1. Explosion, ion acceleration and molecular fragmentation of methane clusters in the pulsed beam of a free-electron laser
Open this publication in new window or tab >>Explosion, ion acceleration and molecular fragmentation of methane clusters in the pulsed beam of a free-electron laser
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2012 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 86, no 3, 033201- p.Article in journal (Refereed) Published
Abstract [en]

X-ray lasers offer new possibilities for creating and probing extreme states of matter. We used intense and short x-ray pulses from the FLASH soft x-ray laser to trigger the explosions of CH4 and CD4 molecules and their clusters. The results show that the explosion dynamics depends on cluster size and indicate a transition from Coulomb explosion to hydrodynamic expansion in larger clusters. The explosion of CH4 and CD4 clusters shows a strong isotope effect: The heavier deuterons acquire higher kinetic energies than the lighter protons. This may be due to an extended inertial confinement of deuterons vs. protons near a rapidly charging cluster core during exposure.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-180987 (URN)10.1103/PhysRevA.86.033201 (DOI)000308286600008 ()
Available from: 2012-09-14 Created: 2012-09-14 Last updated: 2017-12-07Bibliographically approved
2. TOF-OFF: A method for determining focal positions in tightly focused free-electron laser experiments by measurement of ejected ions
Open this publication in new window or tab >>TOF-OFF: A method for determining focal positions in tightly focused free-electron laser experiments by measurement of ejected ions
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2011 (English)In: High Energy Density Physics, ISSN 1574-1818, Vol. 7, no 4, 336-342 p.Article in journal (Refereed) Published
Abstract [en]

Pulse intensities greater than 1017 Watt/cm2 were reached at the FLASH soft X-ray laser in Hamburg, Germany, using an off-axis parabolic mirror to focus 15 fs pulses of 5–70 μJ energy at 13.5 nm wavelength to a micron-sized spot. We describe the interaction of such pulses with niobium and vanadium targets and their deuterides. The beam produced craters in the solid targets, and we measured the kinetic energy of ions ejected from these craters. Ions with several keV kinetic energy were observed from craters approaching 5 μm in depth when the sample was at best focus. We also observed the onset of saturation in both ion acceleration and ablation with pulse intensities exceeding 1016 W/cm2, when the highest detected ion energies and the crater depths tend to saturate with increasing intensity.

A general difficulty in working with micron and sub-micron focusing optics is finding the exact focus of the beam inside a vacuum chamber. Here we propose a direct method to measure the focal position to a resolution better than the Rayleigh length. The method is based on the correlation between the energies of ejected ions and the physical dimensions of the craters. We find that the focus position can be quickly determined from the ion time-of-flight (TOF) data as the target is scanned through the expected focal region. The method does not require external access to the sample or venting the vacuum chamber. Profile fitting employed to analyze the TOF data can extend resolution beyond the actual scanning step size.

Keyword
X-ray free-electron laser, FLASH, Ion acceleration, Time-of-flight ion spectrometry, Ablation, Crater formation, Focus determination
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-166857 (URN)10.1016/j.hedp.2011.06.008 (DOI)000298040400020 ()
Available from: 2012-01-17 Created: 2012-01-16 Last updated: 2016-04-12Bibliographically approved
3. Modeling of soft X-ray induced ablation in solids
Open this publication in new window or tab >>Modeling of soft X-ray induced ablation in solids
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2011 (English)In: DAMAGE TO VUV, EUV, AND X-RAY OPTICS III, 2011, Vol. 8077Conference paper, Published paper (Refereed)
Abstract [en]

Powerful free electron lasers (FELs) operating in the soft X-ray regime are offering new possibilities for creating and probing materials under extreme conditions. We describe here simulations to model the interaction of a focused FEL pulse with metallic solids (niobium, vanadium, and their deuterides) at 13.5 nm wavelength (92 eV) with peak intensities between 10(15) to 10(18) W/cm(2) and a fixed pulse length of 15 femtoseconds (full width at half maximum). The interaction of the pulse with the metallic solids was modeled with a non-local thermodynamic equilibrium code that included radiation transfer. The calculations also made use of a self-similar isothermal fluid model for plasma expansion into vacuum. We find that the time-evolution of the simulated critical charge density in the sample results in a critical depth that approaches the observed crater depths in an earlier experiment performed at the FLASH free electron laser in Hamburg. The results show saturation in the ablation process at intensities exceeding 10(16) W/cm(2). Furthermore, protons and deuterons with kinetic energies of several keV have been measured, and these concur with predictions from the plasma expansion model. The results indicate that the temperature of the plasma reached almost 5 million K after the pulse has passed.

Series
Proceedings of SPIE, Volym 8077
Keyword
X-ray free electron laser; plasma; ion acceleration; ablation; non - local thermodynamics equilibrium
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-169711 (URN)10.1117/12.888988 (DOI)
Conference
Conference on Damage to VUV, EUV, and X-ray Optics III
Note

Conference on Damage to VUV, EUV, and X-ray Optics III, Prague, CZECH REPUBLIC, APR 18-20, 2011

Available from: 2012-03-05 Created: 2012-03-05 Last updated: 2016-04-12
4. Saturated ablation in metal hydrides and acceleration of protons and deuterons to keV energies with a soft-x-ray laser
Open this publication in new window or tab >>Saturated ablation in metal hydrides and acceleration of protons and deuterons to keV energies with a soft-x-ray laser
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2011 (English)In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 83, no 1, 016403- p.Article in journal (Refereed) Published
Abstract [en]

Studies of materials under extreme conditions have relevance to a broad area of research, including planetary physics, fusion research, materials science, and structural biology with x-ray lasers. We study such extreme conditions and experimentally probe the interaction between ultrashort soft x-ray pulses and solid targets (metals and their deuterides) at the FLASH free-electron laser where power densities exceeding 1017 W/cm2 were reached. Time-of-flight ion spectrometry and crater analysis were used to characterize the interaction. The results show the onset of saturation in the ablation process at power densities above 1016 W/cm2. This effect can be linked to a transiently induced x-ray transparency in the solid by the femtosecond x-ray pulse at high power densities. The measured kinetic energies of protons and deuterons ejected from the surface reach several keV and concur with predictions from plasma-expansion models. Simulations of the interactions were performed with a nonlocal thermodynamic equilibrium code with radiation transfer. These calculations return critical depths similar to the observed crater depths and capture the transient surface transparency at higher power densities.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-147776 (URN)10.1103/PhysRevE.83.016403 (DOI)000286759700006 ()
Available from: 2011-03-01 Created: 2011-02-28 Last updated: 2017-12-11Bibliographically approved
5. Explosions of Xenon Clusters in Ultraintense Femtosecond X-Ray Pulses from the LCLS Free Electron Laser
Open this publication in new window or tab >>Explosions of Xenon Clusters in Ultraintense Femtosecond X-Ray Pulses from the LCLS Free Electron Laser
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2012 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 108, no 13, 133401Article in journal (Refereed) Published
Abstract [en]

Explosions of large Xe clusters (< N > similar to 11 000) irradiated by femtosecond pulses of 850 eV x-ray photons focused to an intensity of up to 1017 W/cm(2) from the Linac Coherent Light Source were investigated experimentally. Measurements of ion charge-state distributions and energy spectra exhibit strong evidence for the formation of a Xe nanoplasma in the intense x-ray pulse. This x-ray produced Xe nanoplasma is accompanied by a three-body recombination and hydrodynamic expansion. These experimental results appear to be consistent with a model in which a spherically exploding nanoplasma is formed inside the Xe cluster and where the plasma temperature is determined by photoionization heating.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-180993 (URN)10.1103/PhysRevLett.108.133401 (DOI)000302019600004 ()22540697 (PubMedID)
Available from: 2012-09-14 Created: 2012-09-14 Last updated: 2017-12-07Bibliographically approved
6. Time of Flight Mass Spectrometry to Monitor Sample Expansion in Flash Diffraction Studies on Single Virus Particles
Open this publication in new window or tab >>Time of Flight Mass Spectrometry to Monitor Sample Expansion in Flash Diffraction Studies on Single Virus Particles
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(English)Manuscript (preprint) (Other academic)
National Category
Fusion, Plasma and Space Physics Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-181365 (URN)
Available from: 2012-09-22 Created: 2012-09-22 Last updated: 2014-09-26

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