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Author: Junjie Li Publisher: ISBN: Category : Physics Languages : en Pages :
Book Description
ABSTRACT: The thesis presents the recent development of the 3rd generation femtosecond electron diffractometer in Professor Jim Cao's group and its application to study ultrafast processes in real time. The research activities cover two main subjects: photoinduced structural phase transition (PIPT) in colossal magnetoresistive (CMR) materials and the dynamics of electron emission and the associated residual charge redistribution in targets during the early stage of laser ablation. In the study of PIPT in CMR materials, a direct and real time measurement of photoinduced structure phase transition in single crystal La0.84Sr0.16MnO3 and LaMnO3 was performed by using femtosecond electron diffraction. The melting of orthorhombic lattice ordering under femtosecond optical excitation is found involving two distinct processes with different time scales, an initial fast melting of orthorhombic phase in 3 ps and a subsequent much slower transformation in 50 ps and longer timescales. The fast process can be attributed to the initial melting of orthorhombic phase induced by the Mn-O bond change that is driven by the quenching of the Jahn-Teller distortion following the photo-excitation. The slow process is associated with the growing of newly formed structure domain from excited sites to the neighboring non-excited orthorhombic sites. In the second project, two new techniques, namely femtosecond electron shadow imaging and ultrafast electron deflectometry, were developed. These two complementary techniques provide both a global view and local prospect of the associated transient electric field and charge expansion dynamics. The results reveal that the charge cloud above the target surface is predominantly composed of thermally ejected electrons and the charge cloud expands with a fast front-layer speed exceeding 107 m/s. The average electric field strength of the charge cloud induced by a pump fluence of 2.2 J/cm2 is estimated to be on the order of ~2.4x105 V/m. For the temporal evolution of residual charges on the target, the results show that residual charges in metals can redistribute themselves almost instantly, abiding by the boundary conditions and Maxwell equations in the same way as they would at electrostatic equilibrium condition. However, residual charges in dielectrics are confined within the excited area for hundreds of picoseconds and beyond. These observations provide an experimental support to the alleged coulomb explosion phenomenon in previous studies, as well as a reference for modeling residual charge dynamics. In addition, a 1-D molecular dynamics simulation of coherent lattice motion in laser excited thin film is presented in the last section of this thesis. Using this simulation, both the displacement and expansion at each lattice site along the 1-D atomic chain can be traced as a function of delay time. In particular, the simulation shows that the electronic thermal stress is responsible for driving the lattice motion at the early stage, which matches very well with our FED experimental data obtained in the study of ultrafast heating of free-standing metal films.
Author: Junjie Li Publisher: ISBN: Category : Physics Languages : en Pages :
Book Description
ABSTRACT: The thesis presents the recent development of the 3rd generation femtosecond electron diffractometer in Professor Jim Cao's group and its application to study ultrafast processes in real time. The research activities cover two main subjects: photoinduced structural phase transition (PIPT) in colossal magnetoresistive (CMR) materials and the dynamics of electron emission and the associated residual charge redistribution in targets during the early stage of laser ablation. In the study of PIPT in CMR materials, a direct and real time measurement of photoinduced structure phase transition in single crystal La0.84Sr0.16MnO3 and LaMnO3 was performed by using femtosecond electron diffraction. The melting of orthorhombic lattice ordering under femtosecond optical excitation is found involving two distinct processes with different time scales, an initial fast melting of orthorhombic phase in 3 ps and a subsequent much slower transformation in 50 ps and longer timescales. The fast process can be attributed to the initial melting of orthorhombic phase induced by the Mn-O bond change that is driven by the quenching of the Jahn-Teller distortion following the photo-excitation. The slow process is associated with the growing of newly formed structure domain from excited sites to the neighboring non-excited orthorhombic sites. In the second project, two new techniques, namely femtosecond electron shadow imaging and ultrafast electron deflectometry, were developed. These two complementary techniques provide both a global view and local prospect of the associated transient electric field and charge expansion dynamics. The results reveal that the charge cloud above the target surface is predominantly composed of thermally ejected electrons and the charge cloud expands with a fast front-layer speed exceeding 107 m/s. The average electric field strength of the charge cloud induced by a pump fluence of 2.2 J/cm2 is estimated to be on the order of ~2.4x105 V/m. For the temporal evolution of residual charges on the target, the results show that residual charges in metals can redistribute themselves almost instantly, abiding by the boundary conditions and Maxwell equations in the same way as they would at electrostatic equilibrium condition. However, residual charges in dielectrics are confined within the excited area for hundreds of picoseconds and beyond. These observations provide an experimental support to the alleged coulomb explosion phenomenon in previous studies, as well as a reference for modeling residual charge dynamics. In addition, a 1-D molecular dynamics simulation of coherent lattice motion in laser excited thin film is presented in the last section of this thesis. Using this simulation, both the displacement and expansion at each lattice site along the 1-D atomic chain can be traced as a function of delay time. In particular, the simulation shows that the electronic thermal stress is responsible for driving the lattice motion at the early stage, which matches very well with our FED experimental data obtained in the study of ultrafast heating of free-standing metal films.
Author: Masashi Arita Publisher: BoD – Books on Demand ISBN: 1838818820 Category : Science Languages : en Pages : 102
Book Description
TEM and SEM have contributed greatly to the progress of various research fields, which has been accelerated in the last few decades by highly functional electron microscopes and microscopy. In this tide of microscopy, various microscopic methods have been developed to make clear many unsolved problems, e.g. pulse beam TEM, environmental microscopy, correlative microscopy, etc. In this book, a number of reviews have been collected concerning these subjects. We think that the content in each chapter is impressive, and we hope this book will contribute to future advances in electron microscopy, materials science, and biomedicine.
Author: Christoph Tobias Hebeisen Publisher: ISBN: 9780494590898 Category : Languages : en Pages : 220
Book Description
Ultrafast electron diffraction is a novel pump-probe technique which aims to determine transient structures during photoinduced chemical reactions and other structural transitions. This technique provides structural information at the atomic level of inspection by using an electron pulse as a diffractive probe. The atomic motions of interest happen on the 100 fs = 10-13 s time scale. To observe these atomic motions, a probe which matches this time scale is required. In this thesis, I describe the development of an electron diffractometer which is capable of 200 fs temporal resolution while maintaining high signal level per electron pulse. This was made possible by the construction of an ultra-compact photoactivated 60 keV femtosecond electron gun.Traditional electron pulse characterization methods are unsuitable for high number density femtosecond electron pulses such as the pulses produced by this electron gun. I developed two techniques based on the laser ponderomotive force to reliably determine the duration of femtosecond electron pulses into the sub-100 fs range. These techniques produce a direct cross-correlation trace between the electron pulse and a laser pulse. The results of these measurements confirmed the temporal resolution of the newly developed femtosecond electron diffractometer. This cross-correlation technique was also used to calibrate a method for the determination of the temporal overlap of electron and laser pulses. These techniques provide the pulse diagnostics necessary to utilize the temporal resolution provided by femtosecond electron pulses.Owing to their high charge-to-mass ratio, electrons are a sensitive probe for electric fields. I used femtosecond electron pulses in an electron deflectometry experiment to directly observe the transient charge distributions produced during femtosecond laser ablation of a silicon (100) surface. We found an electric field strength of 3.5 x 106 V/m produced by the emission of 5.3x1011 electrons/cm 2 just 3 ps after an excitation pulse of 5.6 J/cm2. This observation allowed us to rule out Coulomb explosion as the mechanism for ablation under the conditions present in this experiment.
Author: Guo-ping Zhang Publisher: CRC Press ISBN: 1498764290 Category : Science Languages : en Pages : 300
Book Description
This book, the first of this kind, provides a comprehensive introduction to ultrafast phenomena, covering the fundamentals of ultrafast spin and charge dynamics, femtosecond magnetism, all-optical spin switching, and high-harmonic generation. It covers the experimental tools, including ultrafast pump-probe experiments, and theoretical methods including quantum chemistry and density functional theory, both time-independent and time-dependent. The authors explain in clear language how an ultrafast laser pulse is generated experimentally, how it can induce rapid responses in electrons and spins in molecules, nanostructures and solids (magnetic materials and superconductors), and how it can create high-harmonic generation from atoms and solids on the attosecond timescale. They also show how this field is driving the next generation of magnetic storage devices through femtomagnetism, all-optical spin switching in ferrimagnets and beyond, magnetic logic in magnetic molecules, and ultrafast intense light sources, incorporating numerous computer programs, examples, and problems throughout, to show how the beautiful research can be done behind the scene. Key features: · Provides a clear introduction to modern ultrafast phenomena and their applications in physics, chemistry, materials sciences, and engineering. · Presents in detail how high-harmonic generation occurs in atoms and solids. · Explains ultrafast demagnetization and spin switching, a new frontier for development of faster magnetic storage devices. · Includes numerous worked-out examples and problems in each chapter, with real research codes in density functional theory and quantum chemical calculations provided in the chapters and in the Appendices. This book is intended for undergraduate and graduate students, researchers in physics, chemistry, biology, materials sciences, and engineering.
Author: Ahmed H Zewail Publisher: World Scientific ISBN: 9814502111 Category : Science Languages : en Pages : 605
Book Description
These two volumes on Femtochemistry present a timely contribution to a field central to the understanding of the dynamics of the chemical bond. This century has witnessed great strides in time and space resolutions, down to the atomic scale, providing chemists, biologists and physicists with unprecedented opportunities for seeing microscopic structures and dynamics. Femtochemistry is concerned with the time resolution of the most elementary motions of atoms during chemical change - bond breaking and bond making - on the femtosecond (10-15 second) time scale. This atomic scale of time resolution has now reached the ultimate for the chemical bond and as Lord George Porter puts it, chemists are near the end of the race against time. These two volumes cover the general concepts, techniques and applications of femtochemistry.Professor Ahmed Zewail, who has made the pioneering contributions in this field, has from over 250 publications selected the articles for this anthology. These volumes begin with a commentary and a historical chronology of the milestones. He then presents a broad perspective of the current state of knowledge in femtochemistry by researchers around the world and discusses possible new directions. In the words of a colleague, ';it is a must on the reading-list for all of my students ...; all readers will find this to be an informative and valuable overview.';The introductory articles in Volume I provide reviews for both the non-experts as well as for experts in the field. This is followed by papers on the basic concepts. For applications, elementary reactions are studied first and then complex reactions. Volume I is complete with studies of solvation dynamics, non-reactive systems, ultrafast electron diffraction and the control of chemical reactions.Volume II continues with reaction rates, the concept of elementary intramolecular vibrational-energy redistribution (IVR) and the phenomena of rotational coherence which has become a powerful tool for the determination of molecular structure via time resolution. The second volume ends with an extensive list of references, according to topics, based on work by Professor Zewail and his group at Caltech.These collected works by Professor Zewail will certainly be indispensable to both experts and beginners in the field. The author is known for his clarity and for his creative and systematic contributions. These volumes will be of interest and should prove useful to chemists, biologists and physicists. As noted by Professor J Manz (Berlin) and Professor A W Castleman, Jr. (Penn State): femtochemistry is yielding exciting new discoveries from analysis to control of chemical reactions, with applications in many domains of chemistry and related fields, e.g., physical, organic and inorganic chemistry, surface science, molecular biology, ...; etc.
Author: P. Vasa Publisher: Springer ISBN: 3319396145 Category : Science Languages : en Pages : 232
Book Description
This book presents emerging contemporary optical techniques of ultrafast science which have opened entirely new vistas for probing biological entities and processes. The spectrum reaches from time-resolved imaging and multiphoton microscopy to cancer therapy and studies of DNA damage. The book displays interdisciplinary research at the interface of physics and biology. Emerging topics on the horizon are also discussed, like the use of squeezed light, frequency combs and terahertz imaging as the possibility of mimicking biological systems. The book is written in a manner to make it readily accessible to researchers, postgraduate biologists, chemists, engineers, and physicists and students of optics, biomedical optics, photonics and biotechnology.
Author: Kiyoshi Ueda Publisher: Springer Nature ISBN: 9819729149 Category : Laser pulses, Ultrashort Languages : en Pages : 485
Book Description
Zusammenfassung: This book illustrates advanced technologies for imaging electrons and atoms in action in various forms of matter, from atoms and diatoms to protein molecules and condensed matter. The technologies that are described employ ultrafast pulsed lasers, X-ray free electron lasers, and pulsed electron guns, with pulse durations from femtoseconds, suitable to visualize atoms in action, to attoseconds, needed to visualize ballistic electron motion. Advanced theories, indispensable for understanding such ultrafast imaging and spectroscopy data on electrons and atoms in action, are also described. The book consists of three parts. The first part describes probing methods of attosecond electron dynamics in atoms, molecules, liquids, and solids. The second part describes femtosecond structural dynamics and coupling of structural change and electron motion in molecules and solids The last part is dedicated to ultrafast photophysical processes and chemical reactions of protein molecules responsible for biological functions
Author: T. Kamiya Publisher: Springer Science & Business Media ISBN: 3642584691 Category : Science Languages : en Pages : 449
Book Description
Recent rapid advances in femtosecond technology have had a great impact on their industrial applications such as: ultrafast optoelectronic devices and optical telecommunication systems, ultrashort-pulse lasers and measurement systems, and the development of novel materials for ultrafast functions. In this book, a wealth of knowledge covering requirements in applications details of recent achievements in important technical areas is presented by world-prominent authors in a concise, systematic form. As a whole, this is the first comprehensive book on the emerging field of femtosecond technology.
Author: T. Elsaesser Publisher: Springer Science & Business Media ISBN: 3642565468 Category : Science Languages : en Pages : 709
Book Description
This book presents the latest advances in ultrafast science, including ultrafast laser and measurement technology, and studies of ultrafast phenomena. It summarizes the results presented at the 12th Ultrafast Phenomena Conference and reviews the state of the art of this important and rapidly advancing field.
Author: Markus Kitzler Publisher: Springer ISBN: 3319201735 Category : Science Languages : en Pages : 385
Book Description
This book documents the recent vivid developments in the research field of ultrashort intense light pulses for probing and controlling ultrafast dynamics. The recent fascinating results in studying and controlling ultrafast dynamics in ever more complicated systems such as (bio-)molecules and structures of meso- to macroscopic sizes on ever shorter time-scales are presented. The book is written by some of the most eminent experimental and theoretical experts in the field. It covers the new groundbreaking research directions that were opened by the availability of new light sources such as fully controlled intense laser fields with durations down to a single oscillation cycle, short-wavelength laser-driven attosecond pulses and intense X-ray pulses from the upcoming free electron lasers. These light sources allowed the investigation of dynamics in atoms, molecules, clusters, on surfaces and very recently also in nanostructures and solids in new regimes of parameters which, in turn, led to the identification of completely new dynamics and methods for controlling it. Example topics covered by this book include the study of ultrafast processes in large molecules using attosecond pulses, control of ultrafast electron dynamics in solids with shaped femtosecond laser pulses, light-driven ultrafast plasmonic processes on surfaces and in nanostructures as well as research on atomic and molecular systems under intense X-ray radiation. This book is equally helpful for people who would like to step into this field (e.g. young researchers), for whom it provides a broad introduction, as well as for already experienced researchers who may enjoy the exhaustive discussion that covers the research on essentially all currently studied objects and with all available ultrafast pulse sources.
Author: Junjie Li
Author: Junjie Li
Author: Masashi Arita
Author: Christoph Tobias Hebeisen
Author: Guo-ping Zhang
Author: Ahmed H Zewail
Author: P. Vasa
Author: Kiyoshi Ueda
Author: T. Kamiya
Author: T. Elsaesser
Author: Markus Kitzler