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Interaction of Ultrashort X-ray Pulses with Material
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Teknisk-naturvetenskapliga fakulteten, Biologiska sektionen, Institutionen för cell- och molekylärbiologi.
2007 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Uppsala: Acta Universitatis Upsaliensis , 2007. , s. 76
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 356
Emneord [en]
free-electron laser, dense plasma, X-ray, radiation damage, laser physics, nano-plasma, Molecular Dynamics
HSV kategori
Identifikatorer
URN: urn:nbn:se:uu:diva-8274ISBN: 978-91-554-6996-2 (tryckt)OAI: oai:DiVA.org:uu-8274DiVA, id: diva2:170867
Disputas
2007-11-15, B41, BMC, Husargatan 3, Uppsala, 09:00
Opponent
Veileder
Tilgjengelig fra: 2007-10-24 Laget: 2007-10-24bibliografisk kontrollert
Delarbeid
1. Model for the Dynamics of a Water Cluster in an X-ray Free Electron Laser Beam
Åpne denne publikasjonen i ny fane eller vindu >>Model for the Dynamics of a Water Cluster in an X-ray Free Electron Laser Beam
2004 (engelsk)Inngår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 70, nr 5:1, s. 051904-Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

A microscopic sample placed into a focused x-ray free electron laser beam will explode due to strong ionization on a femtosecond time scale. The dynamics of this Coulomb explosion has been modeled by Neutze et al. [Nature (London) 406, 752 (2000)] for a protein, using computer simulations. The results suggest that by using ultrashort exposures, structural information may be collected before the sample is destroyed due to radiation damage. In this paper a method is presented to include the effect of screening by free electrons in the sample in a molecular dynamics simulation. The electrons are approximated by a classical gas, and the electron distribution is calculated iteratively from the Poisson-Boltzmann equation. Test simulations of water clusters reveal the details of the explosion dynamics, as well as the evolution of the free electron gas during the beam exposure. We find that inclusion of the electron gas in the model slows down the Coulomb explosion. The hydrogen atoms leave the sample faster than the oxygen atoms, leading to a double layer of positive ions. A considerable electron density is located between these two layers. The fact that the hydrogens are found to explode much faster than the oxygens means that the diffracting part of the sample stays intact somewhat longer than the sample as a whole.

Emneord
Computer Simulation, Electrons, Lasers, Models
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-96323 (URN)15600653 (PubMedID)
Tilgjengelig fra: 2007-10-24 Laget: 2007-10-24 Sist oppdatert: 2017-12-14bibliografisk kontrollert
2. Soft-x-ray free-electron-laser interaction with materials
Åpne denne publikasjonen i ny fane eller vindu >>Soft-x-ray free-electron-laser interaction with materials
2007 (engelsk)Inngår i: 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. 76, nr 4, s. 046403-Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Soft-x-ray free-electron lasers have enabled materials studies in which structural information is obtained faster than the relevant probe-induced damage mechanisms. We present a continuum model to describe the damage process based on hot-dense plasma theory, which includes a description of the energy deposition in the samples, the subsequent dynamics of the sample, and the detector signal. We compared the model predictions with experimental data and mostly found reasonable agreement. In view of future free-electron-laser performance, the model was also used to predict damage dynamics of samples and optical elements at shorter wavelengths and larger photon fluences than currently available.

HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-96324 (URN)10.1103/PhysRevE.76.046403 (DOI)000250622100073 ()
Tilgjengelig fra: 2007-10-24 Laget: 2007-10-24 Sist oppdatert: 2017-12-14bibliografisk kontrollert
3. Force Field Benchmark of Organic Liquids: Density, Enthalpy of Vaporization, Heat Capacities, Surface Tension, Isothermal Compressibility, Volumetric Expansion Coefficient, and Dielectric Constant
Åpne denne publikasjonen i ny fane eller vindu >>Force Field Benchmark of Organic Liquids: Density, Enthalpy of Vaporization, Heat Capacities, Surface Tension, Isothermal Compressibility, Volumetric Expansion Coefficient, and Dielectric Constant
Vise andre…
2007 (engelsk)Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 98, nr 14, s. 145502-Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

At the recently built FLASH x-ray free-electron laser, we studied the reflectivity of Si/C multilayers with fluxes up to 3×1014W/cm2. Even though the nanostructures were ultimately completely destroyed, we found that they maintained their integrity and reflectance characteristics during the 25-fs-long pulse, with no evidence for any structural changes over lengths greater than 3Å. This experiment demonstrates that with intense ultrafast pulses, structural damage does not occur during the pulse, giving credence to the concept of diffraction imaging of single macromolecules.

Emneord
X-ray effects, Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-96325 (URN)10.1103/PhysRevLett.98.145502 (DOI)000245512100037 ()
Merknad


Tilgjengelig fra: 2007-10-24 Laget: 2007-10-24 Sist oppdatert: 2017-12-14bibliografisk kontrollert
4. Feasibility of imaging living cells at subnanometer resolutions by ultrafast X-ray diffraction
Åpne denne publikasjonen i ny fane eller vindu >>Feasibility of imaging living cells at subnanometer resolutions by ultrafast X-ray diffraction
Vise andre…
2008 (engelsk)Inngår i: Quarterly reviews of biophysics (Print), ISSN 0033-5835, E-ISSN 1469-8994, Vol. 41, nr 3-4, s. 181-204Artikkel, forskningsoversikt (Fagfellevurdert) Published
Abstract [en]

Detailed structural investigations on living cells are problematic because existing structural methods cannot reach high resolutions on non-reproducible objects. Illumination with an ultrashort and extremely bright X-ray pulse can outrun key damage processes over a very short period. This can be exploited to extend the diffraction signal to the highest possible resolution in flash diffraction experiments. Here we present an analysis or the interaction of a very intense and very short X-ray pulse with a living cell, using a non-equilibrium population kinetics plasma code with radiation transfer. Each element in the evolving plasma is modeled by numerous states to monitor changes in the atomic populations as a function of pulse length, wavelength, and fluence. The model treats photoionization, impact ionization, Auger decay, recombination, and inverse bremsstrahlung by solving rate equations in a self-consistent manner and describes hydrodynamic expansion through the ion sound speed, The results show that subnanometer resolutions could be reached on micron-sized cells in a diffraction-limited geometry at wavelengths between 0.75 and 1.5 nm and at fluences of 10(11)-10(12) photonS mu M (2) in less than 10 fs. Subnanometer resolutions could also be achieved with harder X-rays at higher fluences. We discuss experimental and computational strategies to obtain depth information about the object in flash diffraction experiments.

HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-96326 (URN)10.1017/S003358350800471X (DOI)000262098500001 ()
Tilgjengelig fra: 2007-10-24 Laget: 2007-10-24 Sist oppdatert: 2022-01-28bibliografisk kontrollert
5. Interaction of Ultrashort X-ray Pulses with B4C, SiC and Si
Åpne denne publikasjonen i ny fane eller vindu >>Interaction of Ultrashort X-ray Pulses with B4C, SiC and Si
2008 (engelsk)Inngår i: 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, nr 2, s. 026404-1-026404-8Artikkel i tidsskrift (Fagfellevurdert) 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.

Emneord
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
HSV kategori
Identifikatorer
urn:nbn:se:uu:diva-96327 (URN)10.1103/PhysRevE.77.026404 (DOI)000253763800053 ()18352130 (PubMedID)
Tilgjengelig fra: 2007-10-24 Laget: 2007-10-24 Sist oppdatert: 2022-01-28bibliografisk kontrollert

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