Ultrafast Electronic and Structural Dynamics

Inhaltsverzeichnis

1. Frontmatter

2. 1. Attosecond Dynamics of Non-resonant Atomic Photoionization

   David Busto, Shiyang Zhong, Jan Marcus Dahlström, Anne L’Huillier, Mathieu Gisselbrecht

   Abstract

   The interaction of light with matter played a key role in the establishment of quantum mechanics, and each development of new light sources led to important advances in science, technology and society. An exciting area of physics has been opened with the new millennium, attosecond physics, where the motion of electrons can be studied at the fastest time scale ever reached with light. We review the field of non-resonant photoionization of rare gases using attosecond pulses, with an emphasis on the theoretical background of the reconstruction of attosecond beating by interference of two-photon transition (RABBIT) measurement technique. This approach allows the description of photoionization in the time domain while keeping a high spectral resolution. Examples show the status and the progress in the field during the last decade.

3. Chapter 2. Attosecond Interferometry

   Michael Krüger, Nirit Dudovich

   Abstract

   In this chapter, we introduce all-optical attosecond interferometry using high-harmonic generation (HHG). Interferometry provides an access to phase information, enabling the reconstruction of ultrafast electron dynamics with attosecond precision. We discuss two main pathways—internal and external attosecond interferometry. In internal interferometry, the manipulation of quantum paths within the HHG mechanism enables phase-resolved studies of strong-field processes, such as field-induced tunneling. In external interferometry, the phase of the light emitted during the HHG process can be determined using optical interference in the extreme-ultraviolet regime. Both pathways have significantly progressed the state of the art of ultrafast spectroscopy, as evidenced by numerous examples described in this chapter. All-optical attosecond interferometry is applicable to a wide range of systems, such as atomic and molecular gases and condensed-matter systems. Combining the two pathways has the potential to access to hitherto elusive ultrafast multi-electron and chiral phenomena.

4. Chapter 3. Attosecond Dynamics in Liquids

   Hans Jakob Wörner, Axel Schild, Denis Jelovina, Inga Jordan, Conaill Perry, Tran Trung Luu, Zhong Yin

   Abstract

   Attosecond science is well developed for atoms and promising results have been obtained for molecules and solids. Here, we review the first steps in developing attosecond time-resolved measurements in liquids. These advances provide access to time-domain studies of electronic dynamics in the natural environment of chemical reactions and biological processes. We concentrate on two techniques that are representative of the two main branches of attosecond science: pump-probe measurements using attosecond pulses and high-harmonic spectroscopy (HHS). In the first part, we discuss attosecond photoelectron spectroscopy with cylindrical microjets and its application to measure time delays between liquid and gaseous water. We present the experimental techniques, the new data-analysis methods, and the experimental results. We describe in detail the conceptual and theoretical framework required to describe attosecond chronoscopy in liquids at a quantum-mechanical level. This includes photoionization delays, scattering delays, as well as a coherent description of electron transport and (laser-assisted) photoemission and scattering. As a consequence, we show that attosecond chronoscopy of liquids is, in general, sensitive to both types of delays, as well as the electron mean-free paths. Through detailed modeling, involving state-of-the-art quantum scattering and Monte-Carlo trajectory methods, we show that the photoionization delays dominate in attosecond chronoscopy of liquid water at photon energies of 20–30 eV. This conclusion is supported by a near-quantitative agreement between experiment and theory. In the second part, we introduce HHS of liquids based on flat microjets. These results represent the first observation of high-harmonic generation (HHG) in liquids extending well beyond the visible into the extreme-ultraviolet regime. We show that the cut-off energy scales almost linearly with the peak electric field of the driver and that the yield of all harmonics scales non-perturbatively. We also discuss the ellipticity dependence of the liquid-phase harmonics, which is systematically broadened compared to the gas phase. We introduce a strongly driven few-band model as a zero-order approximation of HHG in liquids and demonstrate the sensitivity of HHG to the electronic structure of liquids. Finally, we discuss more advanced approaches for modeling liquid-phase HHG. In the conclusion, we present an outlook on future studies of attosecond dynamics in liquids.

5. Chapter 4. Strong-Field Electron Dynamics in Solids

   Kenichi L. Ishikawa, Yasushi Shinohara, Takeshi Sato, Tomohito Otobe

   Abstract

   Solid-state materials have recently emerged as a new stage of strong-field physics and attosecond science. The mechanism of the electron dynamics driven by an ultrashort intense laser pulse is under intensive discussion. Here we theoretically discuss momentum-space strong-field electron dynamics in graphene and crystalline dielectrics and semiconductors. First, within massless Dirac fermion and tight-binding models for graphene, we rigorously derive intraband displacement and interband transition, which form the basis for understanding solid-state strong-field physics including high-harmonic generation (HHG). Then, based on the time-dependent Schrödinger equation for a one-dimensional model crystal, we introduce a simple, multiband, momentum-space three-step model that incorporates intraband displacement, interband tunneling, and recombination with a valence band hole. We also analyze how the model is modified by electron-hole interaction. Finally, actual three-dimensional materials are investigated. We present a time-dependent density-matrix method whose results for HHG are compared with experimental measurement results. Moreover, we describe the dynamical Franz-Keldysh effect in femtosecond time resolution, i.e., the time-dependent modulation of a dielectric function under an intense laser field, using a real-time time-dependent density functional theory.

6. Chapter 5. Attosecond Space–Time Imaging with Electron Microscopy and Diffraction

   Peter Baum, Yuya Morimoto

   Abstract

   The first step of most light-matter interactions is a field-driven motion of electron density in and around the atoms of a material. Fully visualizing such dynamics and its consequences for the macroscopic functionality of a material, therefore, requires atomic resolution in space and sub-light-cycle resolution in time. Here, we review our latest progress with attosecond space–time imaging by using attosecond electron pulses in diffraction and microscopy. We start with a brief review of recent technological advancements for the temporal compression of ultrashort electron pulses with radio-frequency waves, terahertz pulses and now optical field cycles. We then report on the light-wave control of electron beams at thin metallic or dielectric membranes, which form the basis of attosecond electron imaging in our laboratory. We report the first demonstrations of attosecond electron diffraction and microscopy in proof-of-principle experiment that reveal an upper limit for the delays associated with electron-crystal scattering and visualize the oscillations and propagation of a traveling light wave on a nanometer-thick membrane. These unprecedented space–time resolutions provided by attosecond electron microscopy and diffraction now enable to capture the dynamics of electrons inside of atoms, molecules, crystals or nanostructures as a function of space and time.

7. Chapter 6. Towards Time-Resolved Molecular Orbital Imaging

   Masakazu Yamazaki, Tomoyuki Endo, Akiyoshi Hishikawa, Masahiko Takahashi

   Abstract

   Understanding the mechanism of a chemical reaction is essential for controlling selectivity and yields of products or designing a novel molecular function, which is one of the ultimate goals of chemistry. Since a chemical reaction can be defined as nuclear dynamics driven by the change in electron motion, time-resolved molecular orbital imaging would open the door not only to gain a deeper insight into molecular dynamics but also to advance and extend frontiers of science and technology. In this chapter, two experimental techniques that aim to visualize the changing molecular orbital pattern during a chemical reaction are described in detail. One is the attempt to tackle the issue in momentum space, and the other is the attempt to do the same based on laser tunneling ionization. It is demonstrated that these two techniques are each applicable to short-lived excited states, thereby both offering opportunities for investigating the driving force behind chemical reaction.

8. Chapter 7. Ultrafast X-Ray Scattering: New Views of Chemical Reaction Dynamics

   Peter M. Weber, Brian Stankus, Adam Kirrander

   Abstract

   The advent of ultrafast pulsed X-ray free-electron lasers with very high brightness has enabled the determination of transient molecular structures of small and medium-sized organic molecules in excited states and undergoing chemical dynamics using X-ray scattering. This chapter provides an introduction into X-ray scattering theory and considers several important aspects relating to the experimental implementation. Ultrafast gas phase X-ray scattering is shown to provide new observables to elucidate the dynamics of chemical reactions by providing complete, time-dependent molecular structures. Consideration of correlations between structural parameters is important for molecules far from their equilibrium, and the changes in electron density distributions of molecules upon optical excitation need to be considered in the analysis. Future technological developments are expected to lead to further important advances.

9. Chapter 8. Photochemical Reactions in the Gas Phase Studied by Ultrafast Electron Diffraction

   Jie Yang, Martin Centurion, Xijie Wang, Thomas Wolf, Markus Gühr

   Abstract

   Time-resolved ultrafast electron diffraction (UED) from isolated molecules allows insight into ultrafast quantum wavepacket dynamics of molecules with sub-Angstrom spatial resolution. For the simple example of an excited state vibrational wavepacket in iodine, we can reconstruct the mean atomic distance as a function of delay after the optical excitation. For the case of CF₃I, we can reconstruct the dissociative motion after UV excitation on the A-band states. Furthermore, we also show how the signature of nonadiabatic wavepacket dynamics after two-photon excitation is visible in the diffraction data.

10. Chapter 9. Ultrafast X-ray Spectroscopy for Probing a Nuclear Wavepacket in Photoexcited Molecular Complexes

    Tetsuo Katayama, Thomas J. Penfold, Christian Bressler

    Abstract

    Revealing details of coherent nuclear motion during photochemical reactions on the femtosecond timescale is indispensable for understanding the reaction mechanism in the excited state manifold. Owing to the improvement in time resolution and data quality associated with the advent of X-ray free-electron lasers (XFELs), this can now be achieved with atomic structural sensitivity using time-resolved X-ray absorption near edge structure (TR-XANES) spectroscopy. In this chapter, we describe how vibrational motions are observed and interpreted with this X-ray technique. Femtosecond vibrational modes are studied on two prototypical transition metal complexes, [Fe(bpy)₃]²⁺ (bpy = 2,2′-bipyridine) and [Cu(dmphen)₂]⁺ (dmphen = 2,9-dimethyl-1,10-phenanthroline), and future perspectives exploiting ultrafast X-ray spectroscopies with high repetition rate XFEL machines are presented.

11. Chapter 10. Ultrafast X-Ray Probes of Dynamics in Solids

    Mariano Trigo, Mark P. M. Dean, David A. Reis

    Abstract

    Advances in our ability to understand and utilize the world around us have always relied on the development of advanced tools for probing and manipulating material properties.

12. Chapter 11. Ultrafast Transient Absorption Spectroscopy for Probing Primary Photochemical Reaction of Proteins

    Atsushi Yabushita

    Abstract

    Photochemical reactions of proteins are playing important roles for all life on earth; retinal proteins in retina work as light sensor to provide vision, phytochromes in plants regulate the germination of seeds, photoprotein in fireflies and jelly fishes generates bioluminescence, and chlorophyll triggers carbonic acid assimilation by photosynthesis reaction. Exploration of materials which have better efficiency for those photochemical reactions cannot be performed efficiently by haphazard approach. Elucidation of the primary reaction process is expected to provide key information for the development of future materials. The primary reaction could be studied in detail by performing ultrafast spectroscopy which visualizes spectral change during ultrafast transition between electronic states after photoexcitation. Using ultrashort laser pulse whose duration is shorter than the molecular vibration period, the observed transient absorption signal shows modulation reflecting the real-time motion of the molecular vibration in time domain. Time-gated Fourier analysis of the signal elucidates the time development of the molecular vibration frequency which elucidates molecular structure change during the photo-reaction. Ultrashort pulse lasers in visible and ultraviolet spectral region were developed to be applied for ultrafast spectroscopy of the protein samples to elucidate their primary reactions. For the study of molecular vibrational dynamics, signal fluctuation of the transient absorption should be suppressed to observe fine signal modulation caused by the molecular vibration. However, irradiation of the ultrashort laser pulse required for the ultrafast spectroscopy gives serious damage accumulation especially in the protein samples, which degrades signal quality of the transient absorption. Developing fastscan ultrafast spectroscopy system, we have succeeded to improve the signal-to-noise ratio of the transient absorption signal able to study molecular vibrational dynamics. The ultrashort laser pulse and fastscan ultrafast spectroscopy system to study the primary reaction dynamics of the protein samples. Here we describe some of those works for samples of a light-driven proton pump (bacteriorhodopsin) and a heme protein (nitric oxide synthase).

13. Chapter 12. Time-Resolved Raman Mapping of Energy Flow in Proteins

    Yasuhisa Mizutani, Satoshi Yamashita, Misao Mizuno

    Abstract

    We have summarized our work on time-resolved Raman mapping of protein energy flow. It is not yet clear how energy migrates through proteins. Anti-Stokes ultraviolet resonance Raman (UVRR) spectroscopy has been used to develop techniques to address the characteristics of energy flow. One of the key advantages of UVRR spectroscopy is its high sensitivity to aromatic side chains due to resonance Raman enhancement. This enhancement allows you to observe specific sites on large protein molecules at the level of a single amino acid residue. In addition, anti-Stokes intensity is a selective probe of vibrationally excited populations. These advantages make time-resolved anti-Stokes UVRR spectroscopy ideal for studying the vibrational energy flow of proteins. Our studies on heme proteins demonstrated that the major channel of the excess energy transfer is not through covalent bonds of the main chain but through van der Waals atomic contacts between heme and the probe residue. It was also shown that anti-Stokes spectra of tryptophan residues serve an excellent spectroscopic “thermometer” in terms of high sensitivity and straightforward interpretation.

14. Chapter 13. Ultrafast Two-Dimensional Spectroscopy of Photosynthetic Systems

    Donatas Zigmantas, Tomáš Mančal

    Abstract

    This chapter starts with a review of the theoretical foundation for understanding two-dimensional electronic spectroscopy (2DES) signals in molecular systems. We derive and motivate key properties of 2DES, demonstrating its ability to yield complex information about energy transfer processes and couplings within molecular assemblies, such as photosynthetic antennae. We continue with a discussion encompassing crucial aspects of experimental implementations of 2DES, with particular attention to polarization-controlled experiments. Through illustrative applications of 2DES in studies of light-harvesting functions in isolated complexes and an intact photosyntetic unit in green sulfur bacteria the chapter reveals the extensive insights into the photophysical functions of photosynthetic machinery that can be obtained. Emphasis is placed on identifying exciton coupling, delineating energy transfer pathways, and quantifying rates and efficiencies. The chapter concludes by anticipating future 2DES developments, e.g., the studies on intact photosynthetic units at physiological temperatures, that will contribute to a more holistic comprehension of primary photosynthetic functions, particularly in light harvesting and charge separation.

15. Chapter 14. Vibrational Coherence and Tunneling in Proteins

    Abdelkrim Benabbas, Paul M. Champion

    Abstract

    This chapter discusses the use of vibrational coherence and ultrafast wide-dynamic-range population kinetics to probe biological molecules. We show how impulsive stimulated Raman scattering can be used to develop the method of vibrational coherence spectroscopy, which reveals both the structural and functional aspects of the difficult to detect low-frequency modes (\(h\nu \lesssim {k}_{B}T\)) in proteins. Studies of electron tunneling in cytochrome c as well as the kinetics of the methionine-heme binding reaction are emphasized. Several ultrafast kinetic studies of heme proteins are used to infer the adiabaticity of ligand-heme binding reactions as well as the potential role of heavy atom tunneling (at temperatures below ~60 K). We also examine vibrational coherence and its potential participation in the excited state proton transfer of green fluorescent protein (GFP). We compare three independent observations of vibrational coherence in GFP and conclude that coherent motion does not affect the excited state proton transfer rate that occurs on the ps timescale. For the ground state proton back-transfer reaction, we find that (incoherent) vibrationally assisted proton tunneling is the dominant transport channel and that the tunneling rate is ~400 ps at room temperature. These studies suggest how serine and/or threonine residues may play an important role in controlling biological proton transport along water-based proton wires.

16. Chapter 15. Time-Resolved Studies of Protein Structural Dynamics

    Allen M. Orville, Eriko Nango, So Iwata, Sandra Mous, Joerg Standfuss, Przemyslaw Nogly, Michihiro Suga, Jian-Ren Shen, Minoru Kubo

    Abstract

    Proteins change their conformations in a sophisticated manner when they perform their functions. Time-resolved serial femtosecond crystallography is a potent tool for determining protein dynamic structures.

17. 16. Correction to: Attosecond Dynamics of Non-resonant Atomic Photoionization

    David Busto, Shiyang Zhong, Jan Marcus Dahlström, Anne L’Huillier, Mathieu Gisselbrecht