Atomic and Molecular Dynamics Probed by Intense Extreme Ultraviolet Attosecond Pulses
Atomic and Molecular Dynamics Probed by Intense Extreme Ultraviolet Attosecond Pulses

Author: Jasper Georg Christopher Peschel

Publisher:

Published: 2021

Total Pages:

ISBN-13: 9789180390156

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This thesis work was aimed to investigate dynamical processes in atoms and molecules on ultrafast time scales initiated by absorption of light in the extreme ultraviolet (XUV) regime. In particular, photoionization and photodissociation have been studied using pump-probe techniques involving ultrafast laser pulses. Such pulses are generated using either high-order harmonic generation (HHG) or free-electron lasers (FELs). The work of this thesis consists to a large extent in the development and application of a light source, enabling intense XUV attosecond pulses using HHG. In a long focusing geometry, a high-power infrared laser is frequency up-converted so as to generate a comb of high-order harmonics. An important aspect was the study of the spatial and temporal properties of the generated light pulses in order to gain control of their influence on the experiment. Combining theoretical and experimental results, the effect of the dipole phase on properties of high-order harmonics was explored, along with a metrological series of studies on the harmonic wavefront and the properties of the focusing optics used. Further, the HHG light source was employed to investigate photoionization. Individual angular momentum channels involved in the ionization were characterized using two-photon interferometry in combination with angle-resolved photoelectron detection. A method is applied allowing the full determination of channel-resolved amplitudes and phases of the matrix elements describing the single-photon ionization of neon. Finally, the process of photodissociation was investigated using light pulses generated via both HHG and FELs. The dissociation dynamics induced by multiple ionization of organic molecules were studied. Correlation techniques were used to unravel the underlying fragmentation dynamics, and additionally, pump-probe experiments provided insights into the time scales of the (pre-)dissociation dynamics.

Ultrafast Dynamics Driven by Intense Light Pulses
Ultrafast Dynamics Driven by Intense Light Pulses

Author: Markus Kitzler

Publisher: Springer

Published: 2015-07-24

Total Pages: 385

ISBN-13: 3319201735

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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.

Attosecond Spectroscopic Studies of Atomic and Molecular Dynamics
Attosecond Spectroscopic Studies of Atomic and Molecular Dynamics

Author: Annelise Beck

Publisher:

Published: 2014

Total Pages: 104

ISBN-13:

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Isolated attosecond pulses with photon energies in the extreme ultraviolet have provided a new capability to study few-femtosecond and sub-femtosecond dynamics in atomic and molecular systems. A novel regime of attosecond transient absorption measurements, in which the near-infrared pulse follows the attosecond pulse, is reviewed. The observed timescales of the decay of an absorption feature and oscillations due to quantum beating are derived and experimental considerations for these measurements are discussed. Attosecond transient absorption spectroscopy is then applied to observe quantum beating between the 2s22p5(2P3/2)3d and 2s22p5(2P1/2)3d electronically excited states of neon. The quantum beating is observed more prominently in one of the absorption features, and theoretical models of the effect of the near-infrared pulse are proposed to explain this asymmetry and characterize the observed beating. In the model that most closely agrees with the measurement, the beating is detected via Rabi cycling induced by the near-infrared pulse through an intermediate state (likely one of the 3p states), and this mechanism is shown to be strongly dependent on the spectrum of the near-infrared pulse. The isolated attosecond pulses used in these experiments are characterized using the photoelectron streaking method and the duration of these pulses is measured by iteratively reconstructing the streaking spectrograms. The effect on the streaking spectrogram of various pulse characteristics, such as duration, chirp, and the presence of satellite pulses, is described. Streaking spectrograms using low photon energy attosecond pulses are typically asymmetric. The reasons for this asymmetry are discussed and the challenges of reconstructing these low energy pulses are addressed. Finally, attosecond pulses are used to investigate superexcited states, or doubly excited states above the ionization potential, of the nitrogen molecule (N2). These states can decay via two competing channels, autoionization and predissociation. Time-of-flight mass spectrometry is applied to measure lifetimes of these states. Preliminary results are presented and improvements to the experimental design are proposed.

Femtosecond Molecular Dynamics Studied with Vacuum Ultraviolet Pulse Pairs
Femtosecond Molecular Dynamics Studied with Vacuum Ultraviolet Pulse Pairs

Author: Thomas K. Allison III

Publisher:

Published: 2010

Total Pages: 238

ISBN-13:

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Atoms and molecules have most of their oscillator strength in the vacuum ultraviolet (VUV) and extreme ultraviolet (XUV), between the wavelengths of 200 nm and 30 nm. However, most femtosecond spectroscopy has been restricted to the visible and infrared due to a lack of sufficiently intense VUV and XUV femtosecond light sources. This thesis discusses extensions of pump/probe spectroscopy to the VUV and XUV, and its application to the dynamics of ethylene and oxygen molecules excited at 161 nm. I begin with a detailed discussion of the short wavelength light source used in this work. The source is based on the high order harmonics of a near infrared laser and can deliver> 1010 photons per shot in femtosecond pulses, corresponding to nearly 10 MW peak power in the XUV. Measurements of the harmonic yields as a function of the generation conditions reveal the roles of phase matching and ionization gating in the high order harmonic generation process. Pump/probe measurements are conducted using a unique VUV interferometer, capable of combining two different harmonics at a focus with variable delay. Measurements of VUV multiphoton ionization allows for characterization of the source and the interferometer. In molecules, time resolved measurements of fragment ion yields reveal the femtosecond dynamics of the system. The range of wavelengths available for pump and probe allows the dynamics to be followed from photo-excitation all the way to dissociation without detection window effects. The dynamics in ethylene upon [pi] 2![pi]* excitation are protypical of larger molecules and have thus served as an important test case for advanced ab initio molecular dynamics theories. Femtosecond measurements to date, however, have been extremely lacking. In the present work, through a series of pump probe experiments using VUV and XUV pulses, time scales for the non-adiabatic relaxation of the electronic excitation, hydrogen migration across the double bond, and H2 molecule elimination are measured and compared to theory. In the simpler oxygen molecule, excitation in the Schuman-Runge continuum leads to direct dissociation along the B 3[Sigma]u- potential energy curve. The time resolved photoion spectra show that the total photoionization cross section of the molecule resembles two oxygen atoms within 50 fs after excitation.

Progress in Ultrafast Intense Laser Science
Progress in Ultrafast Intense Laser Science

Author: Kaoru Yamanouchi

Publisher: Springer Science & Business Media

Published: 2013-09-16

Total Pages: 163

ISBN-13: 3319005219

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The PUILS series delivers up-to-date reviews of progress in Ultrafast Intense Laser Science, a newly emerging interdisciplinary research field spanning atomic and molecular physics, molecular science, and optical science, which has been stimulated by the recent developments in ultrafast laser technologies. Each volume compiles peer-reviewed articles authored by researchers at the forefront of each their own subfields of UILS. Every chapter opens with an overview of the topics to be discussed, so that researchers unfamiliar to the subfield, as well as graduate students, can grasp the importance and attractions of the research topic at hand; these are followed by reports of cutting-edge discoveries. This tenth volume covers a broad range of topics from this interdisciplinary research field, focusing on electron scattering by atoms in intense laser fields, atoms and molecules in ultrashort pulsed EUV and X-ray light fields, filamentation induced by intense laser fields, and physics in super-intense laser fields.

XUV Pump-Probe Experiments on Diatomic Molecules
XUV Pump-Probe Experiments on Diatomic Molecules

Author: Kirsten Schnorr

Publisher: Springer

Published: 2014-12-29

Total Pages: 198

ISBN-13: 3319121391

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This book explores the relaxation dynamics of inner-valence-ionized diatomic molecules on the basis of extreme-ultraviolet pump-probe experiments performed at the free-electron laser (FEL) in Hamburg. Firstly, the electron rearrangement dynamics in dissociating multiply charged iodine molecules is studied in an experiment that made it possible to access charge transfer in a thus far unexplored quasimolecular regime relevant for plasma and chemistry applications of the FEL. Secondly the lifetime of an efficient non-radiative relaxation process that occurs in weakly bound systems is measured directly for the first time in a neon dimer (Ne2). Interatomic Coulombic decay (ICD) has been identified as the dominant decay mechanism in inner-valence-ionized or excited van-der-Waals and hydrogen bonded systems, the latter being ubiquitous in all biomolecules. The role of ICD in DNA damage thus demands further investigation, e.g. with regard to applications like radiation therapy.

Ultrafast Chemical Dynamics of Atoms and Molecules Studied by Femtosecond Time-resolved Extreme Ultraviolet Transient Absorption Spectroscopy
Ultrafast Chemical Dynamics of Atoms and Molecules Studied by Femtosecond Time-resolved Extreme Ultraviolet Transient Absorption Spectroscopy

Author: Ming-Fu Lin

Publisher:

Published: 2013

Total Pages: 104

ISBN-13:

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Ultrafast femtosecond (10−15 s) dynamics of atomic xenon, vinyl bromide and carbon disulfide molecules are studied using a newly developed method of extreme ultraviolet (XUV) transient absorption spectroscopy. This research work is devoted to a deeper understanding of the fundamental electronic and nuclear dynamics using XUV light pulses from a high-order harmonic generation source. The produced XUV light pulses are utilized to selectively probe the chemical reaction coordinate with femtosecond temporal resolution. The experimental apparatus for transient absorption pump-probe spectroscopy is described in detail. The research described in this thesis contains four different gaseous atomic and molecular systems. The first system in the study is motivated by a goal to gain a better understanding of the core-excited state couplings of atomic xenon near zero delay between an intense NIR pump pulse (780 nm) and an XUV probe pulse. Secondly, the ionization and dissociation dynamics of molecular vinyl bromide (C2H3Br) under the influence of strong-field ionization are investigated. Finally, an ongoing research project of CS2 and thiophene molecules is presented for future studies of spin-orbit wavepacket and ring-opening dynamics, respectively. The NIR induced core-excited state coupling of atomic xenon is studied using femtosecond XUV transient absorption spectroscopy with photon energies between 50 eV to 70 eV. Coupling of the core-excited states 4d−1(2D5/2)6p(2P3/2) (65.1 eV) and 4d−1(2D3/2)6p(2P1/2) (67.0 eV) to neighboring states by the NIR field results in a threefold enhancement of XUV transmission. The induced transmission at 65.1 eV (67.0 eV) changes from 3.2 ± 0.4% (5.9 ± 0.5%) without the coupling laser to 9 ± 2% (22 ± 5%) at the maximum of the NIR field. A NIR field induced broad XUV absorption feature ranging from 60 eV to 65 eV is explained by the splitting of the field free absorption lines into multiplets when the Rabi frequencies of the coupling transitions higher than the NIR frequency. This assignment is supported by a numerical integration of the von Neumann equation for a few level quantum system. The dissociative ionization dynamics of vinyl bromide, C2H3Br, initiated by a strong laser field ionization are investigated. XUV light pulses with photon energy between 50 eV and 72 eV are utilized to detect the subsequent dynamics. Several dynamic features are observed including the neutral C2H3Br depletion, the formation of C2H3Br ions (X and A states), the production of C2H3Br dications, and the emergence of neutral Br (2P3/2) atoms from dissociative ionization. Free Br (2P3/2) atoms appear on a timescale of 330±150 fs. The singly charged ionic A state displays a time-dependent XUV absorption energy shift of ~0.4 eV during the first 300 fs after strong-filed ionization. The signal intensity from Br atoms correlates with the signal intensity from singly charged parent ions in the A state as a function of NIR laser peak intensity. The experimental observations suggest that vibrationally excited C2H3Br+ (A) ions possibly undergo ultrafast intramolecular vibrational energy redistribution concurrent with the C-Br bond dissociation within a time scale of 330±150 fs. The C2H3Br+ (X) and C2H3Br++ ions are relatively stable as a consequence of deeper potential wells and a high dissociation barrier, respectively. Two ongoing experiments of sulfur-containing molecules are presented that are aimed at future studies of a molecular spin-orbit wavepacket in CS2+ ions and ultrafast ring-opening dynamics of thiophene. Strong-field ionization can coherently populate two spin-orbit states in CS2+ ions. The spin-orbit splitting originates from the atomic sulfur (~60 meV). The small splitting offers the possibility to probe a coherent beating on a time scale of 69 fs, well beyond our temporal resolution of 25 fs. For thiophene, an ultrafast ring-opening process initiated by one-photon excitation at 193 nm is studied through multiphoton ionization at 780 nm. The parent ion population exhibits a fast decay on a time scale of 200±30 fs. This offers a reference for the future XUV transient absorption experiments using one-photon excitation at 193 nm and sulfur (2p) L-edge detection at 165 eV.

Attosecond Molecular Dynamics
Attosecond Molecular Dynamics

Author: Marc J J Vrakking

Publisher: Royal Society of Chemistry

Published: 2018-08-31

Total Pages: 512

ISBN-13: 1782629955

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Attosecond science is a new and rapidly developing research area in which molecular dynamics are studied at the timescale of a few attoseconds. Within the past decade, attosecond pump-probe spectroscopy has emerged as a powerful experimental technique that permits electron dynamics to be followed on their natural timescales. With the development of this technology, physical chemists have been able to observe and control molecular dynamics on attosecond timescales. From these observations it has been suggested that attosecond to few-femtosecond timescale charge migration may induce what has been called "post-Born-Oppenheimer dynamics", where the nuclei respond to rapidly time-dependent force fields resulting from transient localization of the electrons. These real-time observations have spurred exciting new advances in the theoretical work to both explain and predict these novel dynamics. This book presents an overview of current theoretical work relevant to attosecond science written by theoreticians who are presently at the forefront of its development. It is a valuable reference work for anyone working in the field of attosecond science as well as those studying the subject.