Time-resolved diffraction with an optimized short pulse laser plasma X-ray source

We present a set-up for time-resolved X-ray diffraction based on a short pulse, laser-driven plasma X-ray source. The employed modular design provides high flexibility to adapt the set-up to the specific requirements (e.g. X-ray optics, sample environment) of particular applications. The configuration discussed here has been optimized towards high angular/momentum resolution and uses K$_{\alpha}$-radiation (4.51 keV) from a Ti wire-target in combination with a toroidally bent crystal for collection, monochromatization and focusing of the emitted radiation. $2\times 10^5$ Ti-K$_{\alpha1}$ photons per pulse with $10^{-4}$ relative bandwidth are delivered to the sample at 10 Hz repetition rate. This allows for high dynamic range ($10^4$) measurements of transient changes of the rocking curves of materials as for example induced by laser-triggered strain waves.Comment: 29 pages, 8 figure

Electron propagation in solid matter as a result of relativistic laser plasma interactions

This thesis groups heterogeneous results coming from three experiments. The leitmotiv is the electron behaviour in the target during and after the inter- action between a laser pulse and cold target at relativistic intensities. The measurement of the Zeeman effect in the X-ray regime by exploiting the magnetic field created by the interaction of ultra-intense fs laser pulses with solid target will be discussed in the first part. The polarization depen-dence of high resolution X-ray spectra as a tool to infer the electron velocity distribution at relativistic intensities inside the target will be matter of the second part. Finally, in the last part, the electron transport in solid plasma at intensities of about 5×1019 W/cm2 detected by an energy resolving 2D X-ray imaging system will be investigated

Time-resolved X-ray diffraction study on superconducting YBa2Cu3O7 epitaxially grown on SrTiO3

This thesis addresses the lattice response of a compound consisting of a thin superconducting lm and a single crystalline substrate to an ultrafast breaking of superconductivity. The lattice response is investigated by means of time-resolved X-ray diraction. As X-ray source a laser produced plasma is used that emits sub-ps Ka bursts. This thesis is organized in the following way: After an introduction to important issues of the physics of high-temperature superconductors and SrTiO3 as well as their lattice response, the experimental and theoretical methods used in this work are briey introduced. In the following section, the experiment is discussed in more detail. Further, results from both, static and time-resolved experiments are presented. For a theoretical discription of the experimental results several models are developed

Innovative XUV and X.ray Plasma Spectroscopy to explore Warm Dense Matter

Zusammenfassend widmet sich die vorliegende Arbeit der Erforschung definierter Zustaende warmer dichter Materie. Dieses Wissen ist von herausragender Bedeutung für die Laser-Fusions-Forschung, die Erforschung von Materiezustaenden mit hoher Dichte, sowie eine Vielzahl astrophysikalisch-relevanter Fragestellungen der Plasmaforschung. Die vorliegende Arbeit zeigt innovative Methoden der Erzeugung und Charakterisierung warmer dichter Materie auf. Dieser Nicht-Gleichgewichts-Zustand zwischen kaltem Festkoeorper und idealem Plasma wird durch Experimente mit hoher Energiedichte erzeugt. Seine Eigenschaften wurden mit hoher Praezision studiert. Die Erzeugung eines definierten Zustandes warmer dichter Materie mit Hilfe optischer Kurzpluslaser hoher Intensitaeten ist herausfordernd. Energiereiche Elektronen aus einem kleinen, heißen Plasma auf der Targetvorderseite heizen die kalte Materie durch Stoßionisation auf. Hohe spektrale sowie raeumliche Aufloesungen sind noetig, um nicht ueber verschiedene Plasmazustaende zu mitteln. Der Autor wendet hoch entwickelde Roentgenspektroskopie charakteristischer Emissionslinien, gefolgt von numerischer Datenverabeitung, an. Das Ergebnis enthaelt viele Informationen, da die Linienform durch die Plasmaparameter beeinflusst wird und die Roentgenstrahlen zudem transparent für Festkoerperdichte sind. Alternative Wege zur Erzeugung warmer dichter Materie sind momentan im Fokus der Hohe-Energiedichte-Forschung. In der vorliegenden Arbeit wird erstmals die Erzeugung warmer dichter Materie durch direkte Photoionisation gebundener Elektronen mit den Femtosekundenpulsen des weltweit ersten weichen Roentgenlasers FLASH demonstriert. Innerhalb der durch die internationale Peak-Brightness-Collaboration geschaffenen Rahmenbedingungen war der Autor verantwortlich für Pionierarbeiten. Schließlich gelang die erste vollstaendige Charakterisierung warmer dicher Materie an FLASH sowie die erste Demonstration saettigbarer Absorption im weichen Roentgenbereich

Optimization of femtosecond laser plasma Kα sources

Since the night when Conrad RÄontgen ¯rst saw his hand's bones on a °uorescence screen [71] x rays have been one of the most important tools for revealing the inner structure of matter. Beside x-ray imaging for medical diagnosis, the study of x-ray di®raction patterns in chemistry and physics has become a major application of x rays, because it allows the structure of crystalline solids with atomic spatial resolution to be analyzed. Processes which are determined by atomic motion, like chemical reactions and phase transitions, happen on a timescale comparable to the vibrational period of the atoms, which is typically 10¡13 s or 100 fs [76]. The ideal tool to investigate such a process would simultaneously o®er a temporal resolution smaller than this time scale and the ability to resolve the interatomic distances. Until recently, no such tool existed and the investigator had to choose between the femtosecond time resolution of optical spectroscopy with femtosecond lasers and the spatial resolving power of x-ray studies. The experimental method which came closest to the `ideal tool' was time-resolved x-ray di®raction using a synchrotron radiation source. It was especially used to study biologically important processes like the photoinduced trans-cis isomerization of a part of the protein rhodopsin which forms the light detecting process in the human eye [64] or the binding of oxygen and carbon monoxide to myoglobin [94]. These experiments had a nanosecond time resolution which proved to be accurate for the processes under investigation, but all-optical experiments indicate that the initial structural changes, which precede the studied ones, happen much faster, within several ten or hundred femtoseconds [34, 35]. Moreover, optical measurements have revealed that femtosecond time scales are also relevant to processes in solid state physics, like the atomic rearrangement during transitions from one solid phase to another [84] and the disordering of semiconductors after strong electronic excitation by a laser pulse [85]. State-of-the-art synchrotron/streak camera setups achieve a time-resolution of about 1 ps [52]. LO

Spatially-resolved x-ray Scattering Experiments.

In many laboratory astrophysics experiments, intense laser irradiation creates novel material conditions with large, one-dimensional gradients in the temperature, density, and ionization state. X-ray Thomson scattering (XRTS) is a powerful technique for measuring these parameters in dense plasmas. However, the scattered signal has previously been measured with little or no spatial resolution. This limits XRTS to characterizing homogenous plasmas like steady shocks or isochorically heated matter. This dissertation reports on the development of the imaging x-ray Thomson spectrometer diagnostic for the Omega laser facility, which extends XRTS to the general case of plasmas with one-dimensional structure. The diffraction of x-rays from a toroidally-curved crystal creates high-resolution images that are simultaneously spectrally and spatially resolved along a one-dimensional profile. The technique of imaging x-ray Thomson scattering is applied to produce the first measurements of the spatial profiles of the temperature, ionization state, relative material density, and shock speed of a blast wave in a high-energy density system. A decaying shock is probed with 90 degree scattering of 7.8 keV helium-like nickel x-rays. The spatially-resolved scattering is used to infer the material conditions along the shock axis. These measurements enable direct comparison of the temperature as observed with that inferred from other quantities, with good agreement.PHDApplied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/102287/1/eliseo_1.pd

Ultrafast x-ray diffraction for measurements of structural dynamics in shocked metals

An experiment on structural dynamics at the ultrafast time scale in shocked metal samples is presented. The technique development of an ultrafast x-ray diffractometer to generate 'molecular movies' is described. Preliminary results of static x-ray measurements of thin unshocked Ga samples are presented. Initial experiments use 200-300 mJ of a 100fs Ti:Sapphire laser to excite K-alpha x-ray emission in an aluminum wire. The x-ray emission is relayed using a spherical crystal to the sample target. Plans for experiments using Cu K-alpha emission will also be described

Time-resolved X-ray diffraction with accelerator- and laser-plasma-based X-ray sources

Femtosecond X-ray pulses are a powerful tool to investigate atomic motions triggered by femtosecond pump pulses. This thesis is dedicated to the production of such pulses and their use in optical pump – X-ray probe measurement. This thesis describes the laser-plasma-based sources available at the University of Duisburg-Essen. Part of it consists of the description of the design, built-up and characterization of a new “modular” X-ray source dedicated to optimize the X-ray flux onto the sample under investigation. The acoustic wave generation in femtosecond optically excited semiconductor (gallium arsenide) and metal (gold) was performed using the sources of the University of Duisburg-Essen. The physical answer of the material was modeled by a simple strain model for the semiconductor, pressure model for the metal, in order to gain information on the interplay of the electronic and thermal pressures rising after excitation. Whereas no reliable information could be obtain in gallium arsenide (principally due to the use of a bulk), the model for gold achieved very good agreement, providing useful information. The relaxation time of the electron to lattice energy was found to be (5.0±0.3) ps, and the ratio of the Grüneisen parameters was found to be e / i = (0.5±0.1). This thesis also describes the Sub-Picosecond Pulse Source (SPPS) which existed at the (formally) Stanford Linear Accelerator Center, an accelerator-based X-ray source, and two measurements performed with it. The first one is the detailed investigation of the phonon softening of the A1g mode launch in bismuth upon fluence excitation. Detailed information concerning the new equilibrium position and phonon frequency were obtained over extended laser pump fluences. The second measurement concerned the study of the liquid phase dynamics in a newly formed liquid phase following ultrafast melting in indium antimonide. The formation of the liquid phase and its development for excitations close to the ablation threshold were revealed. Such results were possible to obtain, due to the unprecedented combination of a short X-ray pulse duration and brightness at the SPPS