Search

The prospect of single particle imaging with atomic resolution is one of the scientific drivers for the development of X-ray free-electron lasers. The assumption since the beginning has been that damage to the sample caused by intense X-ray pulses is one of the limiting factors of coherent diffractive imaging of single particles and that X-ray pulses need to be as short as possible. Based on molecular dynamics simulations of proteins in X-ray fields of various durations (5 fs, 25 fs and 50 fs), we show that the noise in the diffracted signal caused by radiation damage is less than what can be expected from other sources, such as sample inhomogeneity and X-ray shot-to-shot variations. These findings show a different aspect of the feasibility of single particle imaging using free-electron lasers, where employing X-ray pulses of longer durations could still provide a useful diffraction signal above the noise due to the Coulomb explosion.

Studies of biomolecules have recently seen substantial developments. New X-ray lasers allow for high-resolution imaging of protein crystals too small for conventional X-ray crystallography. Even structures of single particles have been determined at lower resolutions with these new sources. The secret lies in the ultrashort high-intensity pulses, which allow for diffraction and retrieval of structural information before the sample gets fragmented. However, the attainable resolution is still limited, in particular when imaging non-crystalline samples, making further advancements highly desired. In this thesis, some of the resolution-limiting obstacles facing single particle imaging (SPI) of proteins are studied in silico. As the X-ray pulse interacts with injected single molecules, their spatial orientation is generally unknown. Recovering the orientation is essential to the structure determination process, and currently nontrivial. Molecular dynamics simulations show that the Coulomb explosion due to intense X-ray ionization could provide information pertaining to the original orientation. Used in conjunction with current methods, this would lead to an enhanced three-dimensional reconstruction of the protein. Radiation damage and sample heterogeneity constitute considerable sources of noise in SPI. Pulse durations are presently not brief enough to circumvent damage, causing the sample to deteriorate during imaging, and the accuracy of the averaged diffraction pattern is impaired by structural variations. The extent of these effects were studied by molecular dynamics. Our findings suggest that radiation damage in terms of ionization and atomic displacement promotes a gating mechanism, benefiting imaging with longer pulses. Because of this, sample heterogeneity poses a greater challenge and efforts should be made to minimize its impact. X-ray lasers generate pulses with a stochastic temporal distribution of photons, affecting the achievable resolution on a pulse-to-p

Studies of biomolecules have recently seen substantial developments. New X-ray lasers allow for high-resolution imaging of protein crystals too small for conventional X-ray crystallography. Even structures of single particles have been determined at lower resolutions with these new sources. The secret lies in the ultrashort high-intensity pulses, which allow for diffraction and retrieval of structural information before the sample gets fragmented. However, the attainable resolution is still limited, in particular when imaging non-crystalline samples, making further advancements highly desired. In this thesis, some of the resolution-limiting obstacles facing single particle imaging (SPI) of proteins are studied in silico. As the X-ray pulse interacts with injected single molecules, their spatial orientation is generally unknown. Recovering the orientation is essential to the structure determination process, and currently nontrivial. Molecular dynamics simulations show that the Coulomb explosion due to intense X-ray ionization could provide information pertaining to the original orientation. Used in conjunction with current methods, this would lead to an enhanced three-dimensional reconstruction of the protein. Radiation damage and sample heterogeneity constitute considerable sources of noise in SPI. Pulse durations are presently not brief enough to circumvent damage, causing the sample to deteriorate during imaging, and the accuracy of the averaged diffraction pattern is impaired by structural variations. The extent of these effects were studied by molecular dynamics. Our findings suggest that radiation damage in terms of ionization and atomic displacement promotes a gating mechanism, benefiting imaging with longer pulses. Because of this, sample heterogeneity poses a greater challenge and efforts should be made to minimize its impact. X-ray lasers generate pulses with a stochastic temporal distribution of photons, affecting the achievable resolution on a pulse-to-p

The prospect of single particle imaging with atomic resolution is one of the scientific drivers for the development of X-ray free-electron lasers. The assumption since the beginning has been that damage to the sample caused by intense X-ray pulses is one of the limiting factors of coherent diffractive imaging of single particles and that X-ray pulses need to be as short as possible. Based on molecular dynamics simulations of proteins in X-ray fields of various durations (5 fs, 25 fs and 50 fs), we show that the noise in the diffracted signal caused by radiation damage is less than what can be expected from other sources, such as sample inhomogeneity and X-ray shot-to-shot variations. These findings show a different aspect of the feasibility of single particle imaging using free-electron lasers, where employing X-ray pulses of longer durations could still provide a useful diffraction signal above the noise due to the Coulomb explosion.

The prospect of single particle imaging with atomic resolution is one of the scientific drivers for the development of X-ray free-electron lasers. The assumption since the beginning has been that damage to the sample caused by intense X-ray pulses is one of the limiting factors of coherent diffractive imaging of single particles and that X-ray pulses need to be as short as possible. Based on molecular dynamics simulations of proteins in X-ray fields of various durations (5 fs, 25 fs and 50 fs), we show that the noise in the diffracted signal caused by radiation damage is less than what can be expected from other sources, such as sample inhomogeneity and X-ray shot-to-shot variations. These findings show a different aspect of the feasibility of single particle imaging using free-electron lasers, where employing X-ray pulses of longer durations could still provide a useful diffraction signal above the noise due to the Coulomb explosion.

The prospect of single particle imaging with atomic resolution is one of the scientific drivers for the development of X-ray free-electron lasers. The assumption since the beginning has been that damage to the sample caused by intense X-ray pulses is one of the limiting factors of coherent diffractive imaging of single particles and that X-ray pulses need to be as short as possible. Based on molecular dynamics simulations of proteins in X-ray fields of various durations (5 fs, 25 fs and 50 fs), we show that the noise in the diffracted signal caused by radiation damage is less than what can be expected from other sources, such as sample inhomogeneity and X-ray shot-to-shot variations. These findings show a different aspect of the feasibility of single particle imaging using free-electron lasers, where employing X-ray pulses of longer durations could still provide a useful diffraction signal above the noise due to the Coulomb explosion.

Studies of biomolecules have recently seen substantial developments. New X-ray lasers allow for high-resolution imaging of protein crystals too small for conventional X-ray crystallography. Even structures of single particles have been determined at lower resolutions with these new sources. The secret lies in the ultrashort high-intensity pulses, which allow for diffraction and retrieval of structural information before the sample gets fragmented. However, the attainable resolution is still limited, in particular when imaging non-crystalline samples, making further advancements highly desired. In this thesis, some of the resolution-limiting obstacles facing single particle imaging (SPI) of proteins are studied in silico. As the X-ray pulse interacts with injected single molecules, their spatial orientation is generally unknown. Recovering the orientation is essential to the structure determination process, and currently nontrivial. Molecular dynamics simulations show that the Coulomb explosion due to intense X-ray ionization could provide information pertaining to the original orientation. Used in conjunction with current methods, this would lead to an enhanced three-dimensional reconstruction of the protein. Radiation damage and sample heterogeneity constitute considerable sources of noise in SPI. Pulse durations are presently not brief enough to circumvent damage, causing the sample to deteriorate during imaging, and the accuracy of the averaged diffraction pattern is impaired by structural variations. The extent of these effects were studied by molecular dynamics. Our findings suggest that radiation damage in terms of ionization and atomic displacement promotes a gating mechanism, benefiting imaging with longer pulses. Because of this, sample heterogeneity poses a greater challenge and efforts should be made to minimize its impact. X-ray lasers generate pulses with a stochastic temporal distribution of photons, affecting the achievable resolution on a pulse-to-p

The prospect of single particle imaging with atomic resolution is one of the scientific drivers for the development of X-ray free-electron lasers. The assumption since the beginning has been that damage to the sample caused by intense X-ray pulses is one of the limiting factors of coherent diffractive imaging of single particles and that X-ray pulses need to be as short as possible. Based on molecular dynamics simulations of proteins in X-ray fields of various durations (5 fs, 25 fs and 50 fs), we show that the noise in the diffracted signal caused by radiation damage is less than what can be expected from other sources, such as sample inhomogeneity and X-ray shot-to-shot variations. These findings show a different aspect of the feasibility of single particle imaging using free-electron lasers, where employing X-ray pulses of longer durations could still provide a useful diffraction signal above the noise due to the Coulomb explosion.

Studies of biomolecules have recently seen substantial developments. New X-ray lasers allow for high-resolution imaging of protein crystals too small for conventional X-ray crystallography. Even structures of single particles have been determined at lower resolutions with these new sources. The secret lies in the ultrashort high-intensity pulses, which allow for diffraction and retrieval of structural information before the sample gets fragmented. However, the attainable resolution is still limited, in particular when imaging non-crystalline samples, making further advancements highly desired. In this thesis, some of the resolution-limiting obstacles facing single particle imaging (SPI) of proteins are studied in silico. As the X-ray pulse interacts with injected single molecules, their spatial orientation is generally unknown. Recovering the orientation is essential to the structure determination process, and currently nontrivial. Molecular dynamics simulations show that the Coulomb explosion due to intense X-ray ionization could provide information pertaining to the original orientation. Used in conjunction with current methods, this would lead to an enhanced three-dimensional reconstruction of the protein. Radiation damage and sample heterogeneity constitute considerable sources of noise in SPI. Pulse durations are presently not brief enough to circumvent damage, causing the sample to deteriorate during imaging, and the accuracy of the averaged diffraction pattern is impaired by structural variations. The extent of these effects were studied by molecular dynamics. Our findings suggest that radiation damage in terms of ionization and atomic displacement promotes a gating mechanism, benefiting imaging with longer pulses. Because of this, sample heterogeneity poses a greater challenge and efforts should be made to minimize its impact. X-ray lasers generate pulses with a stochastic temporal distribution of photons, affecting the achievable resolution on a pulse-to-p

Studies of biomolecules have recently seen substantial developments. New X-ray lasers allow for high-resolution imaging of protein crystals too small for conventional X-ray crystallography. Even structures of single particles have been determined at lower resolutions with these new sources. The secret lies in the ultrashort high-intensity pulses, which allow for diffraction and retrieval of structural information before the sample gets fragmented. However, the attainable resolution is still limited, in particular when imaging non-crystalline samples, making further advancements highly desired. In this thesis, some of the resolution-limiting obstacles facing single particle imaging (SPI) of proteins are studied in silico. As the X-ray pulse interacts with injected single molecules, their spatial orientation is generally unknown. Recovering the orientation is essential to the structure determination process, and currently nontrivial. Molecular dynamics simulations show that the Coulomb explosion due to intense X-ray ionization could provide information pertaining to the original orientation. Used in conjunction with current methods, this would lead to an enhanced three-dimensional reconstruction of the protein. Radiation damage and sample heterogeneity constitute considerable sources of noise in SPI. Pulse durations are presently not brief enough to circumvent damage, causing the sample to deteriorate during imaging, and the accuracy of the averaged diffraction pattern is impaired by structural variations. The extent of these effects were studied by molecular dynamics. Our findings suggest that radiation damage in terms of ionization and atomic displacement promotes a gating mechanism, benefiting imaging with longer pulses. Because of this, sample heterogeneity poses a greater challenge and efforts should be made to minimize its impact. X-ray lasers generate pulses with a stochastic temporal distribution of photons, affecting the achievable resolution on a pulse-to-p

The study of molecular dynamics involves observations of the motion of nuclei and electrons. While nuclear motion is usually on the picosecond or femtosecond timescale, attosecond precision is necessary to directly observe the motion of electrons. Ultrashort laser pulses have become established as a viable tool for probing femtosecond dynamics by irradiating the target for only extremely short times. This allows snapshots of the motion to be obtained. However, extreme ultraviolet (XUV) or soft X-ray wavelengths are required to generate attosecond pulses. Two light sources that produce ultrashort XUV pulses were used during the work presented in this thesis: the free electron laser in Hamburg (FLASH) and the high-order harmonic generation-based light source at the High-Intensity XUV Beamline in Lund.This thesis describes the application of covariance mapping and pump-probe spectroscopy as tools to investigate molecular dynamics at these XUV light sources. A covariance mapping scheme was implemented in conjunction with a double-sided velocity map imaging spectrometer at the High-Intensity XUV Beamline. Its capabilities were demonstrated in a proof-of-principle experiment on molecular nitrogen. The scheme was subsequently applied to more complex molecules, and results from photoion-photoion covariance mapping of adamantane (C10H16) are presented. The photodissociation behavior of halomethane molecules was investigated with infrared - ultraviolet and ultraviolet - soft X-ray pump-probe schemes during several measurement campaigns at FLASH. While these time-resolved experiments probed dynamics mainly on the picosecond timescale, efforts were made at the High-Intensity XUV Beamline towards attosecond precision XUV-XUV pump-probe experiments. After demonstrating the ability to induce two-photon processes with XUV light, the XUV wavefronts were studied over several experimental campaigns. These campaigns led to a significant reduction of aberrations in the XUV wavefronts. T

The origin of properties in complex systems can often be traced to mechanisms involving charge and energy transfer in only a few embedded molecules. The detailed study of the time evolution of these mechanisms in their original environment is a challenging task. In this thesis we develop experimental tools and methods to enable the study of charge and energy transfer. A new ion and electron momentum imaging spectrometer, along with advanced data treatment methods has been succesfully designed, built and tested. The developed spectrometer is optimized for the measurement of the ion and electron momentum correlation that results from the fragmentation of complex systems, from molecules to molecular clusters.We have conducted photodissociation studies on such complex systems, using the newly developed experimental tools.The use of modern X-ray sources allows to localize the initial energy and charge to sites and/or elements in the system, from where the transfer is initiated.The energy and charge transfer is investigated in molecules by the local (multi-)photon absorption at a controlled site. Among other studies, we investigate the origin of the site-dependence of the fragmentation, be it the population of electronic excited states, conformational isomerization, fast hydrogen evaporation and migration, or secondary breakup. The influence of these processes on the fragmentation are investigated in two ways: through the C1s ionization of chemically distinct carbon sites (ethyl trifluoroacetate), and through the C1s excitation of a model system for conjugated (π) hydrocarbons (1,3 trans butadiene).The migration of charge and transfer of energy in embedded molecular systems is studied by the use of molecular clusters as model systems. The photo-induced energy and charge transport can be facilitated by intermolecular electronic decay, hydrogen migration, proton transfer, the Grotthus mechanism and nuclear rearrangement. The role of these processes in the stabilization and

Single particle imaging (SPI) using X-ray pulses has become increasingly attainable with the advent of high-intensity free electron lasers. Eliminating the need for crystallized samples enables structural studies of molecules previously inaccessible by conventional crystallography. While this emerging technique already demonstrates substantial promise, some obstacles need to be overcome before SPI can reach its full potential. One such problem is determining the spatial orientation of the sample at the time of X-ray interaction. Existing solutions rely on diffraction data and are computationally demanding and sensitive to noise. In this in silico study, we explore the possibility of aiding these methods by mapping the ion distribution as the sample undergoes a Coulomb explosion following the intense ionization. By detecting the ions ejected from the fragmented sample, the orientation of the original sample should be possible to determine. Knowledge of the orientation has been shown earlier to be of substantial advantage in the reconstruction of the original structure. 150 explosions of each of twelve separate systems – four polypeptides with different amounts of surface bound water – were simulated with molecular dynamics (MD) and the average angular distribution of carbon and sulfur ions was investigated independently. The results show that the explosion maps are reproducible in both cases, supporting the idea that orientation information is preserved. Additional water seems to restrict the carbon ion trajectories further through a shielding mechanism, making the maps more distinct. For sulfurs, water has no significant impact on the trajectories, likely due to their higher mass and greater ionization cross section, indicating that they could be of particular interest. Based on these findings, we conclude that explosion data can aid spatial orientation in SPI experiments and could substantially improve the capabilities of the novel technique.

X-ray free electron lasers (XFELs) providing ultrashort intense pulses of X-rays have proven to be excellent tools to investigate the dynamics of radiation-induced dissociation and charge redistribution in molecules and nanoparticles. Coincidence techniques, in particular multi-ion time-of-flight (TOF) coincident experiments, can provide detailed information on the photoabsorption, charge generation, and Coulomb explosion events. Here we review several such recent experiments performed at the SPring-8 Angstrom Compact free electron LAser (SACLA) facility in Japan, with iodomethane, diiodomethane, and 5-iodouracil as targets. We demonstrate how to utilize the momentum-resolving capabilities of the ion TOF spectrometers to resolve and filter the coincidence data and extract various information essential in understanding the time evolution of the processes induced by the XFEL pulses.

Die vorliegende Dissertation berichtet über neue Erkenntnisse bei der Elektronenionisation von reinen Heliumtröpfchen und präsentiert vorläufige Daten, die auf Coulombexplosion als Grund für das Auftreten von überwiegend leichten Ionen in Massenspektren und den Ausstoß von Dotanten hinweisen. Weiters konnte gezeigt werden, dass die Entstehung von He+ bei Energien unter der Ionisationsschwelle durch Interaktion von He* mit He*- abläuft, wodurch dieser Prozess zum ersten Mal präzise erklärt werden konnte. Zusätzlich werden Publikationen präsentiert in welchen Elektronenwechselwirkungen benutzt werden um dotierte Tröpfchen zu studieren. Zuerst werden Resultate erörtert, in welchen Elektronen als Instrument benutzt werden um die Position von Dotanten zu bestimmen. Die Ergebnisse zeigen, dass Alkalis, welche normalerweise nicht in Heliumtröpfchen eintauchen, durch das Hinzufügen von einem Fulleren, das sich im Inneren des Tröpfchens befindet, solvatisiert werden kann. Sogar kleine Cäsiumcluster (beginnend mit dem Dimer) können durch die Wechselwirkung mit einem Ko-Dotanten von suprafluidem Helium benetzt werden. Das ist besonders überraschend, da bis dato alle Studien über die Interaktion von Cäsium mit suprafluidem Helium eine extreme Abstoßung zeigen. Resultate zur Wechselwirkung zwischen He*- mit Fulleren-Clustern werden ebenso diskutiert. Ein Zweielektronentransfer führt zu der Entstehung von Dianionen und das Hinzufügen eines weiteren Dotanten zur Stabilisierung von Clustergrößen unter einem gewissen Schwellwert. Abschließend wird eine Publikation über Ionen-Molekülreaktionen, ausgelöst durch Elektronenionisation, zwischen Clustern bestehend aus H2/D2 und O2, präsentiert, die zur Entstehung von besonders stabilem HO4+ bzw. DO4+ führten. Diese Spezien könnten als Markermoleküle zur Detektion von Sauerstoff im interstellaren Medium dienen. Ansätze zu weiteren Studien welche zu einem besseren Verständnis von Elektronenionisation von reinen Heliumtröpfchen führen und da, This thesis reports on new insights on electron ionization of pristine helium droplets and presents preliminary data indicating Coulomb explosion, as the reason for the appearance of predominately low mass ions in mass spectra and the ejection of dopants. Furthermore, it could be shown that the formation of He+ at subthreshold energies proceeds through the interaction of \He * with He *-, which was the first time this process could be explained rigorously. Additionally, publications are presented where electron interactions are used to study doped droplets. At first, results are discussed where electrons are used as a tool to probe the locations of dopants. The findings show that alkali metals, which usually do not submerge into the droplets can be solvated due to the addition of a fullerene that resides in the droplets inside. Even small clusters of cesium (starting from the dimer) can be wet by superfluid helium due to the interaction with a co-dopant. This is especially surprising since all studies to date about the interaction of bulk cesium and superfluid helium report an extreme no-wetting behaviour. Results about the interaction of He *- with clusters of fullerenes are discussed. A concerted two-electron transfer leads to the formation of dianions, with another dopant leading to the stabilization of cluster sizes below a certain threshold. Finally, a publication about ion-molecule reactions between clusters of H2/D2, and O2 initiated by electron ionization that led to the formation of especially stable HO4+ and DO4+ respectively, is shown. These species might serve as tracer molecules for the detection of oxygen in the interstellar medium. Ideas about further studies are suggested, which could lead to a better insight into electron ionization of pristine helium droplets and extend the knowledge gained in the presented publications., von Michael Renzler, MSc, Kumulative Dissertation aus fünf Artikeln, Kurzfassung in deutscher Sprache, In den Artikeln + und - hochgestellt, 4 tiefgestellt, Universität Innsbruck, Dissertation, 2016, OeBB, (VLID)1400677

La versión de editor/PDF no puede utilizarse. Debe enlazar a la versión de editor con DOI. Author's post-print must be released with a Creative Commons Attribution Non-Commercial No Derivatives License, [EN] We have investigated plasma formation and relaxation dynamics induced by single femtosecond laser pulses at the surface of crystalline SiO 2 (quartz) along with the corresponding topography modifications. The use of fs-resolved pump-probe microscopy allows combining spatial and temporal resolution and simultaneous access to phenomena occurring in adjacent regions excited with different local fluences. The results show the formation of a transient free-electron plasma ring surrounding the location of the inner ablation crater. Optical microscopy measurements reveal a 30% reflectivity decrease in this region, consistent with local amorphization. The accompanying weak depression of ¿15 nm in this region is explained by gentle material removal via Coulomb explosion. Finally, we discuss the timescales of the plasma dynamics and its role in the modifications produced, by comparing the results with previous studies obtained in amorphous SiO 2 (fused silica). For this purpose, we have conceived a new representation concept of time-resolved microscopy image stacks in a single graph, which allows visualizing quickly suble differences of the overall similar dynamic response of both materials. © 2011 Elsevier B.V.

We report the observation of sequential Penning ionization of dopants by metastable helium atoms in helium nano-droplets resulting in doubly charged ions. Strong charge induced dipole-interaction between the excited helium atom and the target ion provides a high probability for the transfer of the internal energy of the excited helium atom to the dopant ion. This process may also lead subsequently to a Coulomb explosion of molecular or cluster dopants.

The photo-fragmentation of ammonia molecular clusters ionized with soft x-rays is studied for photon energies near the N-1s threshold. The fragmentation is studied with a 3D momentum mass spectrometer to access the energy and angular correlations between fragments. By choosing the cluster sizes below or above the critical size of stable dication, we investigate the coulomb explosion dynamics and the interplay between charge delocalization and mobility of molecules in the clusters.

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

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

La versión de editor/PDF no puede utilizarse. Debe enlazar a la versión de editor con DOI. Author's post-print must be released with a Creative Commons Attribution Non-Commercial No Derivatives License, [EN] We have investigated plasma formation and relaxation dynamics induced by single femtosecond laser pulses at the surface of crystalline SiO 2 (quartz) along with the corresponding topography modifications. The use of fs-resolved pump-probe microscopy allows combining spatial and temporal resolution and simultaneous access to phenomena occurring in adjacent regions excited with different local fluences. The results show the formation of a transient free-electron plasma ring surrounding the location of the inner ablation crater. Optical microscopy measurements reveal a 30% reflectivity decrease in this region, consistent with local amorphization. The accompanying weak depression of ¿15 nm in this region is explained by gentle material removal via Coulomb explosion. Finally, we discuss the timescales of the plasma dynamics and its role in the modifications produced, by comparing the results with previous studies obtained in amorphous SiO 2 (fused silica). For this purpose, we have conceived a new representation concept of time-resolved microscopy image stacks in a single graph, which allows visualizing quickly suble differences of the overall similar dynamic response of both materials. © 2011 Elsevier B.V.

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

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

We have performed an analysis of ultra-intense laser interaction with solid mass-limited targets (MLT) via electrodynamic 2D3V particle-in-cell simulations. The interaction with long (300 fs) high intensity (1020W=cm2) laser pulses with targets of diameter down to 1 micron is described in detail with respect to electron dynamics and proton and ion acceleration. Depending on the foil diameter, different effects consecutively arise. Electrons laterally recirculate within the target, smoothening the target rear accelerating sheath and increasing the hot electron density and temperature. We developed an analytical model which enables us to predict the electron energy distribution of an MLT. Our results suggest that the most signicant ion energy enhancement should be expected for MLT with diameter below the laser focal spot size. The spread of energetic protons is decreased for medium sized foils while it is greatly increased for foils of size near the focal spot size.

We have performed an analysis of ultra-intense laser interaction with solid mass-limited targets (MLT) via electrodynamic 2D3V particle-in-cell simulations. The interaction with long (300 fs) high intensity (1020W=cm2) laser pulses with targets of diameter down to 1 micron is described in detail with respect to electron dynamics and proton and ion acceleration. Depending on the foil diameter, different effects consecutively arise. Electrons laterally recirculate within the target, smoothening the target rear accelerating sheath and increasing the hot electron density and temperature. We developed an analytical model which enables us to predict the electron energy distribution of an MLT. Our results suggest that the most signicant ion energy enhancement should be expected for MLT with diameter below the laser focal spot size. The spread of energetic protons is decreased for medium sized foils while it is greatly increased for foils of size near the focal spot size.

The fragmentation of deuterated benzene (CA) in ultrashort intense laser fields (9 fs, 1 x 10(15) W/cm(2)) is studied by the ion-coincidence momentum imaging technique. Five two-body and eight three-body Coulomb explosion pathways from the trication (C6D63+), associated with the deprotonation and ring-opening reactions, are identified. It is found from the fragment momentum correlation that all the observed three-body explosion processes proceed sequentially via the two-body Coulomb explosion forming molecular dications, CmDn2+, with (m,n) = (6,5), (5,5), (5,4), (4,4), (4,3), and (3,3), which further dissociate into pairs of monocations. The branching ratio of the fragmentation pathways estimated from the number of the observed coincidence events indicates that the fragmentation is nonstatistical., authorCount :5

We analytically calculate the number of particles arriving per unit time at a detector some distance away from a hot Coulomb explosion site. The result depends only on few parameters and permits to determine the initial temperature and maximum potential energy from a fit.

Correlation detection techniques (image labeling, coincidence imaging, and joint variance) are developed with an image spectrometer capable of collecting charges ejected over 4\pi sr and a digital camera synchronized with the laser repetition rate at up to 735 Hz. With these techniques, molecular decay channels ejecting atomic fragments with different momenta (energies) can be isolated; thus the initial molecular configurations (bond lengths and/or bond angles) and orientations as well as their distributions can be extracted. These techniques are applied to study strong-field induced dynamics of diatomic and triatomic molecules. Specific studies included the measurements of the Coulomb explosion energy as a function of bond angle in linear (CO_2) and bent (NO_2) triatomics and the ejection anisotropy relative to the laser polarization axis during Coulomb explosions in both triatomic (CO_2 and NO_2) and diatomic (H_2, N_2 and O_2) systems. The experiments were performed with 100 fs, 800 nm laser pulses focused to 0.1 ~ 5 \times 10^15 W/cm^2. The explosion energy of NO_2 decreases monotonically by more than 25% from the smallest to the largest bond angle. By contrast, the CO_2 explosion energies are nearly independent of bond angle. The enhanced-ionization and static-screening models in two-dimension with three charge centers were developed to simulate the explosion energies as a function of bond angle. The predictions are consistent with the measurements of CO_2 and NO_2. The observed explosion signals as a function of bond angle for both triatomics show large-amplitude vibrations. The ejection angular distributions in triatomic (CO_2 and NO_2) and diatomic (H_2, N_2, and O_2) Coulomb explosions were measured; the contribution made to the ejection anisotropy by dynamic alignment was studied by comparing the images obtained with linearly and circularly polarized fields. Different angular distributions of the molecules are consistent with different ionization stages, i

In order to improve the geometrical characterization of molecular ions using the Coulomb Explosion Imaging method, we discuss the need to include wake effects in a full description of the interactions felt by the swift dissociated atomic ions moving through thin foils. Comparison of simulations and experimental results for the structure of diatomic (HD+) and triatomic (CH2+) molecular ions is significantly improved when including the polarization effects induced in the target by the passage of swift ions.

In order to improve the geometrical characterization of molecular ions using the Coulomb Explosion Imaging method, we discuss the need to include wake effects in a full description of the interactions felt by the swift dissociated atomic ions moving through thin foils. Comparison of simulations and experimental results for the structure of diatomic (HD+) and triatomic (CH2+) molecular ions is significantly improved when including the polarization effects induced in the target by the passage of swift ions.

The effect of target polarization fields on the bond-angle distribution following the foil-induced Coulomb explosion of CH2+ has been measured. Incorporating a detailed model description of the polarization effects and other target effects into a Monte Carlo simulation of the experiment, a good description of the various observables is obtained. In particular, the bond-angle distribution is found to agree with existing ab initio calculations.

The effect of target polarization fields on the bond-angle distribution following the foil-induced Coulomb explosion of CH2+ has been measured. Incorporating a detailed model description of the polarization effects and other target effects into a Monte Carlo simulation of the experiment, a good description of the various observables is obtained. In particular, the bond-angle distribution is found to agree with existing ab initio calculations.

We report on the possibility to produce homonuclear vibrationally cold molecular ion beams (using D as an example) via the interaction of cold electrons with a stored beam. We demonstrate that cooling of the vibrational degrees of freedom can be achieved within a reasonable time, which is comparable to the beam lifetime. We also present preliminary results on the electron impact vibrational excitation of HD+. (C) 2003 Elsevier Science B.V. All rights reserved.

The electric field in mm-sized one-component non-neutral plasmas is measured using the Stark effect of Rydberg atoms embedded in them. The plasmas are clouds of cold Rb(+)-ions, which are produced by UV photoionization of laser-cooled Rb atoms in a magneto-optic trap. The dependence of the electric field on the number of ions and the Coulomb explosion of the ion clouds have been studied., This article is from CP06, Non-Neutral Plasma Physics IV, p89-95, 2001. Pub. in AIP Conference Proceedings: volume 606. Prepared in cooperation with Ernst-Moritz-Arndt-Universitaet, Greifswald, Germany. This article is from ADA404831 Non-Neutral Plasma Physics 4. Workshop on Non-Neutral Plasmas (2001) Held in San Diego, California on 30 July-2 August 2001

The Coulomb explosion of the proton fragments dissociated from H2+ molecules moving through thin aluminum foils has been studied by means of their energy spectra, measured in the forward direction, and by computer simulations. The covered energy range goes from 25 to 100 keV/u. Estimations of the neutral charge fraction of the fragments inside the foil have been obtained by comparison of the experimental energy spectra with the computer simulations.

The Coulomb explosion of the proton fragments dissociated from H2+ molecules moving through thin aluminum foils has been studied by means of their energy spectra, measured in the forward direction, and by computer simulations. The covered energy range goes from 25 to 100 keV/u. Estimations of the neutral charge fraction of the fragments inside the foil have been obtained by comparison of the experimental energy spectra with the computer simulations.