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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.
Over the past few decades, the rapid development of ultrafast lasers, such as femtosecond lasers and picosecond lasers, has opened up new avenues for material processing due to their unique features such as ultrashort pulse width and extremely high peak intensity. These techniques have become a common tool for micro- and nanoprocessing of a variety
This book covers the state of the art of laser micro- and nanotechnology. The physical fundamentals of different processes and the application are presented. The book deals with different materials like phase change and memory alloys, thin films, polymers etc. New phenomena and mechanisms of laser-matter interaction in nano-domains are explained. This book is helpful for students, postgraduates, engineers and researches working not only in the field of laser microtechnology but also in high-tech industry, like photonics, microelectronics, information technology.
Pulsed laser–based techniques for depositing and processing materials are an important area of modern experimental and theoretical scientific research and development, with promising, challenging opportunities in the fields of nanofabrication and nanostructuring. Understanding the interplay between deposition/processing conditions, laser parameters, as well as material properties and dimensionality is demanding for improved fundamental knowledge and novel applications. This book introduces and discusses the basic principles of pulsed laser–matter interaction, with a focus on its peculiarities and perspectives compared to other conventional techniques and state-of-the-art applications. The book starts with an overview of the growth topics, followed by a discussion of laser–matter interaction depending on laser pulse duration, background conditions, materials, and combination of materials and structures. The information outlines the foundation to introduce examples of laser nanostructuring/processing of materials, pointing out the importance of pulsed laser–based technologies in modern (nano)science. With respect to similar texts and monographs, the book offers a comprehensive review including bottom-up and top-down laser-induced processes for nanoparticles and nanomicrostructure generation. Theoretical models are discussed by correlation with advanced experimental protocols in order to account for the fundamentals and underline physical mechanisms of laser–matter interaction. Reputed, internationally recognized experts in the field have contributed to this book. In particular, this book is suitable for a reader (graduate students as well as postgraduates and more generally researchers) new to the subject of pulsed laser ablation in order to gain physical insight into and advanced knowledge of mechanisms and processes involved in any deposition/processing experiment based on pulsed laser–matter interaction. Since knowledge in the field is given step by step comprehensively, this book serves as a valid introduction to the field as well as a foundation for further specific readings.
Laser Processing and Chemistry gives an overview of the fundamentals and applications of laser-matter interactions, in particular with regard to laser material processing. Special attention is given to laser-induced physical and chemical processes at gas-solid, liquid-solid, and solid-solid interfaces. Starting with the background physics, the book proceeds to examine applications of laser techniques in micro-machining, and the patterning, coating, and modification of material surfaces. This fourth edition has been revised and enlarged to cover new topics such as 3D microfabrication, advances in nanotechnology, ultrafast laser technology and laser chemical processing (LCP). Graduate students, physicists, chemists, engineers, and manufacturers alike will find this book an invaluable reference work on laser processing.
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.
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.
Bringing together contributions from leading experts in the field, this book reviews laser processing concepts that allow the structuring of material beyond optical limits, and methods that facilitate direct observation of the underlying mechanisms by exploring direct structuring and self-organization phenomena. The capacity to nanostructure material using ultrafast lasers lays the groundwork for the next generation of flexible and precise material processing tools. Rapid access to scales of 100 nm and below in two and three dimensions becomes a factor of paramount importance to engineer materials and to design innovative functions. To reflect the dynamic nature of the field at all levels from basic science to applications, the book is divided into three parts, Fundamental Processes, Concepts of Extreme Nanostructuring, and Applications, each of which is comprehensively covered. This book will be a useful resource for graduate students and researchers in laser processing, materials engineering, and nanoscience.
This book presents an Ultrafast Low-Energy Electron Diffraction (ULEED) system that reveals ultrafast structural changes on the atomic scale. The achievable temporal resolution in the low-energy regime is improved by several orders of magnitude and has enabled the melting of a highly-sensitive, molecularly thin layer of a polymer crystal to be resolved for the first time. This new experimental approach permits time-resolved structural investigations of systems that were previously partially or totally inaccessible, including surfaces, interfaces and atomically thin films. It will be of fundamental importance for understanding the properties of nanomaterials so as to tailor their properties.