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Interaction of Ultrashort X-ray Pulses with B4C, SiC and Si
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Molecular biophysics.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Molecular biophysics.
2008 (English)In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 77, no 2, 026404-1-026404-8 p.Article in journal (Refereed) Published
Abstract [en]

The interaction of 32.5 and 6 nm ultrashort x-ray pulses with the solid materials B4C, SiC, and Si is simulated with a nonlocal thermodynamic equilibrium radiation transfer code. We study the ionization dynamics as a function of depth in the material and modifications of the opacity during irradiation, and estimate the crater depth. Furthermore, we compare the estimated crater depth with experimental data, for fluences up to 2.2 J/cm(2). Our results show that, at 32.5 nm irradiation, the opacity changes by less than a factor of 2 for B4C and Si and by a factor of 3 for SiC, for fluences up to 200 J/cm(2). At a laser wavelength of 6 nm, the model predicts a dramatic decrease in opacity due to the weak inverse bremsstrahlung, increasing the crater depth for high fluences.

Place, publisher, year, edition, pages
2008. Vol. 77, no 2, 026404-1-026404-8 p.
Keyword [en]
boron compounds, bremsstrahlung, elemental semiconductors, high-speed optical techniques, ionisation, laser beam effects, opacity, silicon, silicon compounds, thermodynamics, wide band gap semiconductors, X-ray effects
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:uu:diva-96327DOI: 10.1103/PhysRevE.77.026404ISI: 000253763800053PubMedID: 18352130OAI: oai:DiVA.org:uu-96327DiVA: diva2:170866
Available from: 2007-10-24 Created: 2007-10-24 Last updated: 2013-02-27Bibliographically approved
In thesis
1. Interaction of Ultrashort X-ray Pulses with Material
Open this publication in new window or tab >>Interaction of Ultrashort X-ray Pulses with Material
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Radiation damage limits the resolution in imaging experiments. Damage is caused by energy deposited into the sample during exposure. Ultrashort and extremely bright X-ray pulses from free-electron lasers (FELs) offer the possibility to outrun key damage processes, and temporarily improve radiation tolerance. Theoretical models indicate that high detail-resolutions could be realized on non-crystalline samples with very short pulses, before plasma expansion.

Studies presented here describe the interaction of a very intense and ultrashort X-ray pulse with material, and investigate boundary conditions for flash diffractive imaging both theoretically and experimentally. In the hard X-ray regime, predictions are based on particle simulations with a continuum formulation that accounts for screening from free electrons.

First experimental results from the first soft X-ray free-electron laser, the FLASH facility in Hamburg, confirm the principle of flash imaging, and provide the first validation of our theoretical models. Specifically, experiments on nano-fabricated test objects show that an interpretable image can be obtained to high resolution before the sample is vaporized. Radiation intensity in these experiments reached 10^14 W/cm^2, and the temperature of the sample rose to 60000 Kelvin after the 25 femtosecond pulse left the sample. Further experiments with time-delay X-ray holography follow the explosion dynamics over some picoseconds after illumination.

Finally, this thesis presents results from biological flash-imaging studies on living cells. The model is based on plasma calculations and fluid-like motions of the sample, supported by the time-delay measurements. This study provides an estimate for the achievable resolutions as function of wavelength and pulse length. The technique was demonstrated by our team in an experiment where living cells were exposed to a single shot from the FLASH soft X-ray laser.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 76 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 356
Keyword
free-electron laser, dense plasma, X-ray, radiation damage, laser physics, nano-plasma, Molecular Dynamics
National Category
Biophysics
Identifiers
urn:nbn:se:uu:diva-8274 (URN)978-91-554-6996-2 (ISBN)
Public defence
2007-11-15, B41, BMC, Husargatan 3, Uppsala, 09:00
Opponent
Supervisors
Available from: 2007-10-24 Created: 2007-10-24Bibliographically approved

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Timneanu, Nicusor

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