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X-ray diffraction is an invaluable tool in the field of structural dynamics. In the work described in this thesis, time-resolved X-ray diffraction experiments were carried out to investigate ultrafast lattice dynamics. Ultrashort laser pulses were used to induce non-thermal melting and large-amplitude strain waves, and X-rays were used to probe these phenomena. Non-thermal melting was studied in indium antimonide (InSb). It was found that the inertial model, which states that the motion of the atoms is determined by their initial vibrational energy at the time of laser irradiation, accurately describes the process of non-thermal melting. It was demonstrated that the model is valid over a large range of temperatures, from 35 to 500 K, when taking the zero-point energy into account at low temperatures. It was also shown how the process of non-thermal melting can be used as a timing monitor to determine the relative timing of laser and X-ray beams in pump/probe experiments. It was shown how the use of an opto-acoustic transducer could reduce the duration of an Xray pulse. The transducer was made of a thin gold film deposited on the surface of bulk InSb. Upon heating the thin gold film with an ultrashort laser pulse, a strain wave was generated in the semiconductor. This resulted in a modulated phonon spectrum and X-ray reflectivity. It was shown that a 100 ps long X-ray pulse can be transformed to a 20 ps pulse with an 8% efficiency. A large-amplitude strain wave was generated in graphite using an ultrashort laser pulse to elucidate the potential role of strain in phase transitions. The temporal evolution of the strain wave was mapped, and the pressure deduced. It was found that it was possible to induce a pressure and temperature corresponding to the region in the carbon phase diagram in which diamond can form.
Nonlinear Optics, Quantum Optics, and Ultrafast Phenomena with X-Rays is an introduction to cutting-edge science that is beginning to emerge on state-of-the-art synchrotron radiation facilities and will come to flourish with the x-ray free-electron lasers currently being planned. It is intended for the use by scientists at synchrotron radiation facilities working with the combination of x-rays and lasers and those preparing for the science at x-ray free-electron lasers. In the past decade synchrotron radiation sources have experienced a tremendous increase in their brilliance and other figures of merit. This progress, driven strongly by the scientific applications, is still going on and may actually be accelerating with the advent of x-ray free-electron lasers. As a result, a confluence of x-ray and laser physics is taking place, due to the increasing importance of laser concepts, such as coherence and nonlinear optics to the x-ray community and the importance of x-ray optics to the laser-generation of ultrashort pulses of x-rays.
Recent technological advances in synchrotron and neutron sources, detectors, and computer hardware and software have made possible diffraction techniques which collect data at successive moments in time. This is the first book to bring together reviews and research articles covering the three branches of time-resolved diffraction--X-ray, electron, and neutron field. Time-Resolved Diffraction covers gases, liquids, amorphous solids, fibers, and crystals and does so in a multidisciplinary framework which includes examples from molecular biology and chemistry, as well as techniques from physics and materials science. The various time scales of data collection cover ten orders of magnitude, from the sub-pico domain to the kilosecond. Research scientists and graduate students will find this book the most complete compendium of work in this developing field.
Coherent x-ray di raction is an attractive tool for studying a wide range of condensed matter systems due to the many unique advantages of x-rays - small wavelengths, large penetration depths, and chemical and elemental specifity. Soft x-rays are particularly important for the study of magnetism, as many of the important magnetic elements have strong resonances in this regime. This dissertation discusses two sets of coherent x-ray experiments. The first part focuses on the development of time-resolved optical pump x-ray probe experiments both at a synchrotron and an x-ray free electron laser (XFEL) source. Using this technique, I studied the femto- to picosecond relaxation dynamics in the labyrinth-like magnetic domains of a Co/Pd multilayer thin film following excitation by a femtosecond optical pulse. From the normalized correlation function, I isolated the elastic and fluctuating portions of the scattering intensity during the relaxation process. The emergence of XFELs such as the Linac Coherent Light Source has dramatically altered the types of experiments that are now possible, including the systematic exploration of nonlinear x-ray-matter interactions. Nonlinear spectroscopy in the optical regime has contributed immensely to our understanding of microscopic interactions and dynamical processes. The hope is to extend these spectroscopic techniques to the x-ray regime, to take advantage of the smaller wavelength, elemental and chemical specificity, and momentum resolution. One of the most promising nonlinear x-ray techniques is stimulated resonant inelastic x-ray scattering (RIXS), analogous to stimulated Raman scattering in the optical regime. The critical question is whether the threshold for stimulated RIXS will be low enough, below the sample damage threshold, for it to be a viable technique for systems of interest. In the second half of this dissertation, I demonstrate strong indications of stimulated RIXS in a high intensity single shot coherent di raction experiment at LCLS. By utilizing the strong resonant enhancements of the scattering cross-section, significant nonlinear changes in the di raction as a function of x-ray pulse intensity were detected. These observations are consistent with calculated intensities for a stimulated inelastic scattering process. Further intensity dependent spectroscopy experiments are planned for LCLS to con rm the threshold for stimulated scattering. The development of nonlinear x-ray spectroscopic techniques will certainly revolutionize existing fields as well as spawn entirely new fields of research.
The diffraction profiles and density correlation functions are calculated for transient atomic configurations generated in molecular dynamics simulations of a 20 nm Au film irradiated with 200 fs laser pulses of different intensity. The results of the calculations provide an opportunity to directly relate the detailed information on the atomic-level structural rearrangements available from the simulations to the diffraction spectra measured in time-resolved x-ray and electron diffraction experiments. Three processes are found to be responsible for the evolution of the diffraction profiles. During the first several picoseconds after the laser excitation, the decrease of the intensity of the diffraction peaks is largely due to the increasing amplitude of thermal atomic vibrations and can be well described by the Debye-Waller factor. The effect of thermoelastic deformation of the film prior to melting is reflected in shifts and splittings of the diffraction peaks, providing an opportunity for experimental probing of the ultrafast deformations. Finally, the onset of the melting process results in complete disappearance of the crystalline diffraction peaks. The homogeneous nucleation of a large number of liquid regions throughout the film is found to be more effective in reducing long-range correlations in atomic positions and diminishing the diffraction peaks as compared to the heterogeneous melting by melting front propagation. For the same fraction of atoms retaining the local crystalline environment, the diffraction peaks are more pronounced in heterogeneous melting. A detailed analysis of the real space correlations in atomic positions is also performed and the atomic-level picture behind the experimentally observed fast disappearance of the correlation peak corresponding to the second nearest neighbors in the fcc lattice during the laser heating and melting processes is revealed.
This open access book, edited and authored by a team of world-leading researchers, provides a broad overview of advanced photonic methods for nanoscale visualization, as well as describing a range of fascinating in-depth studies. Introductory chapters cover the most relevant physics and basic methods that young researchers need to master in order to work effectively in the field of nanoscale photonic imaging, from physical first principles, to instrumentation, to mathematical foundations of imaging and data analysis. Subsequent chapters demonstrate how these cutting edge methods are applied to a variety of systems, including complex fluids and biomolecular systems, for visualizing their structure and dynamics, in space and on timescales extending over many orders of magnitude down to the femtosecond range. Progress in nanoscale photonic imaging in Göttingen has been the sum total of more than a decade of work by a wide range of scientists and mathematicians across disciplines, working together in a vibrant collaboration of a kind rarely matched. This volume presents the highlights of their research achievements and serves as a record of the unique and remarkable constellation of contributors, as well as looking ahead at the future prospects in this field. It will serve not only as a useful reference for experienced researchers but also as a valuable point of entry for newcomers.
This work focuses on complementary crystallographic and spectroscopic areas of dynamic structural science, from papers presented at the 46th NATO sponsored course in Erice, Sicily 2013. These papers cover a range of material from background concepts to more advanced material and represent a fully inter-disciplinary collection of the latest ideas and results within the field. They will appeal to practising or novice crystallographers, both chemical and biological, who wish to learn more about modern spectroscopic methods and convergent advances and hence vice versa for experimental and computational spectroscopists. The chapters refer to the latest techniques, software and results and each chapter is fully referenced. The volume provides an excellent starting point for new comers in the emerging, multi-disciplinary area of time resolved science.