Joachim Stohr – författare

This book gives a comprehensive account of modern x-ray science, based on the use of synchrotron radiation and x-ray-free electron lasers (XFELs). It emphasizes the new capabilities of XFELs which extend the study of matter to the intrinsic timescales associated with the motion of atoms and chemical transformations and give birth to the new field of non-linear x-ray science. Starting with the historical understanding of the puzzling nature of light, it covers the modern description of the creation, properties, and detection of x-rays within quantum optics. It then presents the formulation of the interactions of x-rays with atomic matter, both, from semi-classical and first-principles quantum points of view. The fundamental x-ray processes and techniques, absorption, emission, Thomson, and resonant scattering (REXS and RIXS) are reviewed with emphasis on simple intuitive pictures that are illustrated by experimental results. Concepts of x-ray imaging and diffractive imaging of atomic and nano structures are discussed, and the quantum optics formulation of diffraction is presented that reveals the remarkable quantum substructure of light. The unique power of x-rays in providing atom and chemical-bond specific information and separating charge and spin phenomena through x-ray polarization (dichroism) effects are highlighted. The book concludes with the discussion of many-photon or non-linear x-ray phenomena encountered with XFELs, such as stimulated emission and x-ray transparency.

Volume I of the second edition, subtitled Semi-Classical Concepts, presents x-ray science through the semi-classical framework of light and matter.The opening chapter, Introduction and Overview, remains largely unchanged from the first edition. It sets the stage for both volumes of the new edition by reviewing the revolutionary advances in x-ray science driven by synchrotron radiation sources and x-ray free-electron lasers. The following chapters are organized into two parts. Part I establishes the equivalence between wave-based and conventional quantum descriptions of light, which form the foundation of the semi-classical approach. It also discusses the generation of synchrotron and XFEL radiation, now extended to recent accelerator breakthroughs that enable the creation of diffraction- and transform-limited x-ray pulses reaching into the attosecond regime.Part II applies the semi-classical treatment to describe how x-rays interact with matter, whether through an individual atomic or collective dielectric response. Topics include x-ray absorption, dichroism, emission, scattering, and diffraction, extensively illustrated with experimental results. Special emphasis is placed on polarization-dependent, resonant responses—key to the unique atomic and chemical specificity of x-rays and their ability to probe the charge and spin structure of matter. The final chapter explores real-space and diffractive imaging techniques, with a focus on solving the phase problem through holography, over-sampling, ptychography, and multi-wavelength anomalous diffraction.An appendix provides reference material, including physical symbols, SI units and values, resonant line shapes, the Dirac d-function, and a concise overview of Fourier transform methods and Parseval’s theorem.

Volume II of the second edition, subtitled Beyond Semi-Classical Concepts, expands the description of x-rays into the framework of quantum optics, rooted in the full theory of light and matter: quantum electrodynamics (QED). Following a brief introduction, the book is organized into three parts and an appendix.Part I explores the description of x-rays and diffraction phenomena within the advanced formalism of quantum optics. The discussion extends conventional quantum mechanics, which treats photons as independent particles, to higher-order quantum states containing multiple photons. A central theme is the emerging paradigm that quantum states with two or more photons can be directly observed in diffraction experiments using multi-photon detection. This makes it possible to overcome constraints of the classical framework, such as the diffraction limit, and to probe novel effects including photon–photon entanglement and interference.Part II presents the quantum formulation of weak photon–matter interactions using the Kramers–Heisenberg–Dirac perturbation framework. This is applied to polarization-dependent, first-principles descriptions of interaction cross sections for x-ray absorption and dichroism, x-ray emission, Thomson scattering, and both resonant elastic (REXS) and inelastic (RIXS) scattering. A new section introduces the derivation of cross sections for two-photon x-ray absorption and ionization.Part III extends the discussion from weak to strong interactions of x-rays with atoms and solids. Topics include the time-dependent transfer of x-ray energy to the electronic system and the lattice, the challenges of sample damage, and the intriguing phenomenon of x-ray transparency. Resonant core-to-valence excitations are analyzed using the optical Bloch equations, revealing effects such as Rabi oscillations of electronic populations and the intensity-dependent emergence of stimulated x-ray scattering. An extensive appendix provides reference materials, including units and physical constants, the calculation of electronic transition matrix elements, and a survey of important quantum states of light and their matrix elements with photon creation and destruction operators encountered in the quantum formulation of diffraction.

This text book gives a comprehensive account of magnetism, one of the oldest yet most vibrant fields of physics. Perhaps uniquely, it discusses spin transport and magnetization dynamics phenomena associated with atomically and spin engineered nano-structures. It does this against the backdrop of spintronics and magnetic storage and memory applications. In addition to summarizing developments in this new field of research the book also discusses magnetism applying synchrotron radiation. In short, the book reviews the fundamental physical concepts of the subject and uses them in a coherent fashion to explain some of the problems and applications at the forefront of magnetism. The book is written for undergraduate and graduate level students, and it should also serve as a state-of-the-art reference for scientists in academia and research laboratories.