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Fragmentation Of Molecular Ions In Ultrafast Laser Pulses
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Book Synopsis Fragmentation of Molecular Ions in Ultrafast Laser Pulses by : Utuq Ablikim
Download or read book Fragmentation of Molecular Ions in Ultrafast Laser Pulses written by Utuq Ablikim and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Imaging the interaction of molecular ion beams with ultrafast intense laser fields is a very powerful method to understand the fragmentation dynamics of molecules. Femtosecond laser pulses with different wavelengths and intensities are applied to dissociate and ionize molecular ions, and each resulting fragmentation channel can be studied separately by implementing a coincidence three-dimensional (3D) momentum imaging method. The work presented in this master's report can be separated into two parts. First, the interaction between molecular ion beams and femtosecond laser pulses, in particular, the dissociation of CO into C+O, is studied. For that purpose, measurements are conducted at different laser intensities and wavelengths to investigate the possible pathways of dissociation into C+O. The study reveals that CO+ starts to dissociate from the quartet electronic state at low laser intensities. Higher laser intensity measurements, in which a larger number of photons can be absorbed by the molecule, show that the doublet electronic states with deeper potential wells, e.g. A2[pi], contribute to the dissociation of the molecule. In addition, the three-body fragmentation of CO2+ into C++O++O+ is studied, and two breakup scenarios are separated using the angle between the sum and difference of the momentum vectors of two O+ fragments. In the second part, improvements in experimental techniques are discussed. Development of a reflective telescope setup intended to increase the conversion efficiency of ultraviolet (UV) laser pulse generation is described, and the setup is used in the studies of CO+ dissociation described in this report. The other technical study presented here is the measurement of the position dependence of timing signals picked off of a microchannel plate (MCP) surface. The experimental method is presented and significant time spread over the surface of the MCP detector is reported [1].
Book Synopsis Dissociation Dynamics of Molecular Ions in Ultrafast, Intense Laser Fields by : Bethany Jochim
Download or read book Dissociation Dynamics of Molecular Ions in Ultrafast, Intense Laser Fields written by Bethany Jochim and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Out of the many tools for probing molecular dynamics, intense, ultrafast laser pulses are particularly well suited for this purpose. First, these pulses have temporal durations shorter than the typical rotational and vibrational periods of molecules and therefore allow the observation of molecular dynamics on their native timescales. Further, the broad bandwidth and high peak intensities of these laser pulses can result in the excitation of many transition pathways that may interfere and enable control of dynamics. The primary focus of this work is the ultrafast laser-induced dissociation of molecular ions. We generate these ions as "fast" beam targets and study their fragmentation using a coincidence three-dimensional (3D) momentum imaging technique, which allows the measurement of all nuclear fragments, including neutrals. This approach is employed to study laser-induced processes in a variety of molecules. The goal of these efforts is not to study specific molecules but rather to use them as testing grounds to deepen our knowledge of laser-induced molecular dynamics in general. For example, we find that permanent-dipole transitions, which are commonly overlooked in the interpretation of strong-field experiments, play a key role in laser-induced dissociation of metastable NO2+ ions. General consideration of these transitions in heteronuclear molecules is important in building our understanding towards more complex molecules. Speaking of more complex systems, we have also begun investigating the laser-induced dynamics of simple hydrocarbons. Our use of molecular ion beam targets gives us the unique ability to exercise control over the initial "configuration," i.e., geometry of these molecules. Utilizing C2H2^q ion beam targets (where q is the molecular ion charge state) prepared in various initial configurations, including acetylene (HCCH), vinylidene (H2CC), and cis/trans, we have determined that this property has an immense impact on the isomerization dynamics, a finding that we anticipate will lead to future work towards deeper understanding. More broadly, this approach of probing molecules in different initial configurations offers a unique perspective that could be complementary to mainstream methods-not just in the case of C2H2 but other chemical systems as well. We also describe some improvements to the 3D momentum imaging methods that facilitate the study of molecular dynamics. One of these developments is a method to distinguish and evaluate the momenta of neutral-neutral channels resulting from the fragmentation of negative ion beams. The second is a technique for imaging the breakup of long-lived metastable molecules decaying in flight to the detector and retrieving the lifetime(s) of the populated states. Our collaborative efforts in adaptive closed-loop control are also discussed. Here, an evolutionary learning algorithm supplied with experimental feedback obtains optimally-shaped ultrashort laser pulses for driving targeted molecular dynamics. While the complexity of the shaped pulses can make interpretation challenging, the combination of these efforts with basic experiments like those we perform using ion beams can help. In closing, the work presented in this thesis extends from diatomic to polyatomic molecules, following the natural progression of building from simpler to more complex systems. We believe that the results of these efforts aid in the advancement of understanding strong-field molecular dynamics and will stimulate future research endeavors along these directions.
Book Synopsis Imaging of Slow Dissociation of the Laser Induced Fragmentation of Molecular Ions by : Bishwanath Gaire
Download or read book Imaging of Slow Dissociation of the Laser Induced Fragmentation of Molecular Ions written by Bishwanath Gaire and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Lasers are being used widely for the study and manipulation of the dynamics of atomic and molecular targets, and advances in laser technology makes it possible to explore new areas of research -- for example attosecond physics. In order to probe the fragmentation dynamics of molecular ions, we have developed a coincidence three-dimensional momentum imaging method that allows the kinematically complete study of all fragments except electrons. Recent upgrades to this method allow the measurement of slow dissociation fragments, down to nearly zero velocity, in intense ultrafast laser fields. Evidences for the low energy breakup are presented using the benchmark molecules diatomic H[subscript]2[superscript]+ and polyatomic H[subscript]3[superscript]+ . The low energy fragments in H[subscript]2[superscript]+ dissociation are due to the intriguing zero-photon dissociation phenomenon. This first experimental evidence for the zero-photon dissociation is further supported by sophisticated theoretical treatment. We have explored the laser pulse length, intensity, wavelength, and chirp dependence of zero-photon dissociation of H[subscript]2[superscript]+, and the results are well described by a two-photon process based on stimulated Raman scattering. Similar studies of the slow dissociation of H[subscript]3[superscript]+ reveal that two-body dissociation is dominant over three-body dissociation. The most likely pathways leading to low-energy breakup into H[superscript]++H[subscript]2, in contradiction to the assessments of the channels in at least one previous study, are explored by varying the laser pulse duration and the wavelength. In addition, we have investigated the dissociation and single ionization of N[subscript]2[superscript]+, and an interesting high energy feature in addition to the low energy has been observed at higher intensities. Such high energy results from the breakup of molecules in excited states are accessible at higher intensities where their potential energy is changing rapidly with the internuclear distance. We have extended the intense field ionization studies to other molecular ions N[subscript]2[superscript]+, CO[superscript]+, NO[superscript]+, and O[subscript]2[superscript]+ . The dissociative ionization of these molecules follow a general mechanism, a stairstep ionization mechanism. Utilizing the capability of the upgraded experimental method we have measured the non-dissociative and dissociative ionization of CO[superscript]+ using different pulse lengths. The results suggest that dissociative ionization can be manipulated by suppressing some ionization paths.
Book Synopsis Measurements of Ultrashort Intense Laser-induced Fragmentation of Simple Molecular Ions by : A. Max Sayler
Download or read book Measurements of Ultrashort Intense Laser-induced Fragmentation of Simple Molecular Ions written by A. Max Sayler and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Present laser technology allows for the production of ultra short (& 7 fs) intense (.1016 W/cm2)pulses, which are comparable in duration and interaction strength to the vibrational period and the interaction that binds the electron in molecules, respectively. In this intense-field ultra short-pulse regime one can both measure and manipulate dynamics on the femtosecond timescale. To probe the dynamics of laser-matter interactions in this regime, we have chosen to start from the simplest possible molecule - H2, which can either dissociate into H + p or ionize into p + p + e. We have designed and employ a coincidence three-dimensional momentum imaging technique which allows us to measure ionization and dissociation of a molecular ion beam target simultaneously, while completely separating the two channels from each other. By varying the laser intensity and the pulse duration, we measure the intensity and pulse length dependent momentum distributions for laser induced fragmentation of H2 at 790 nm. These dissociation measurements are in agreement with the phenomena predicted using the adiabatic Floquet picture, e.g. bond softening, in addition to more sophisticated calculations done by solving the time-dependent Schrodinger equation in the Born-Oppenheimer representation. Furthermore, the structure seen in ionization in our measurements and soon after by others is explained via a unified diabatic Floquet picture, which includes both ionization and dissociation in a single intensity and wavelength dependent picture that includes nuclear motion. Additionally, we use the same experimental techniques and apparatus to probe the laser-induced dynamics of multi-electron diatomic molecules, e.g. O2+, N2+, and ND+. The most probable dissociation and ionization pathways producing the features seen in these measurements are discerned using the angular and kinetic-energy-release distributions in conjunction with the diabatic Floquet picture. Finally, we extend these experimental techniques and interpretive models to the simplest polyatomic molecule - H3+, whose fragmentation presents challenges both in our first-of-their-kind experiments and in physical interpretation.
Book Synopsis Progress in Ultrafast Intense Laser Science II by : See Leang Chin
Download or read book Progress in Ultrafast Intense Laser Science II written by See Leang Chin and published by Springer Science & Business Media. This book was released on 2007-06-10 with total page 378 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book series addresses a newly emerging interdisciplinary research field, Ultrafast Intense Laser Science, spanning atomic and molecular physics, molecular science, and optical science. Highlights of this second volume include Coulomb explosion and fragmentation of molecules, control of chemical dynamics, high-order harmonic generation, propagation and filamentation, and laser-plasma interaction. All chapters are authored by foremost experts in their fields.
Book Synopsis Quantum Control of Molecular Fragmentation in Strong Laser Field by : Mohammad Zohrabi
Download or read book Quantum Control of Molecular Fragmentation in Strong Laser Field written by Mohammad Zohrabi and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Present advances in laser technology allow the production of ultrashort ([similar to or less than]5 fs, approaching single cycle at 800 nm), intense tabletop laser pulses. At these high intensities laser-matter interactions cannot be described with perturbation theory since multiphoton processes are involved. This is in contrast to photodissociation by the absorption of a single photon, which is well described by perturbation theory. For example, at high intensities ([similar to or less than]5 X 10[superscript]13 W/cm[superscript]2) the fragmentation of molecular hydrogen ions has been observed via the absorption of three or more photons. In another example, an intriguing dissociation mechanism has been observed where molecular hydrogen ions seem to fragment by apparently absorbing no photons. This is actually a two photon process, photoabsorption followed by stimulated emission, resulting in low energy fragments. We are interested in exploring these kinds of multiphoton processes. Our research group has studied the dynamics and control of fragmentation induced by strong laser fields in a variety of molecular targets. The main goal is to provide a basic understanding of fragmentation mechanisms and possible control schemes of benchmark systems such as H[subscript]2[superscript]+. This knowledge is further extended to more complex systems like the benchmark H[subscript]3[superscript]+ polyatomic and other molecules. In this dissertation, we report research based on two types of experiments. In the first part, we describe laser-induced fragmentation of molecular ion-beam targets. In the latter part, we discuss the formation of highly-excited neutral fragments from hydrogen molecules using ultrashort laser pulses. In carrying out these experiments, we have also extended experimental techniques beyond their previous capabilities. We have performed a few experiments to advance our understanding of laser-induced fragmentation of molecular-ion beams. For instance, we explored vibrationally resolved spectra of O[subscript]2[superscript]+ dissociation using various wavelengths. We observed a vibrational suppression effect in the dissociation spectra due to the small magnitude of the dipole transition moment, which depends on the photon energy --- a phenomenon known as Cooper minima. By changing the laser wavelength, the Cooper minima shift, a fact that was used to identify the dissociation pathways. In another project, we studied the carrier-envelope phase (CEP) dependences of highly-excited fragments from hydrogen molecules. General CEP theory predicts a CEP dependence in the total dissociation yield due to the interference of dissociation pathways differing by an even net number of photons, and our measurements are consistent with this prediction. Moreover, we were able to extract the difference in the net number of photons involved in the interfering pathways by using a Fourier analysis. In terms of our experimental method, we have implemented a pump-probe style technique on a thin molecular ion-beam target and explored the feasibility of such experiments. The results presented in this work should lead to a better understanding of the dynamics and control in molecular fragmentation induced by intense laser fields.
Book Synopsis Progress in Ultrafast Intense Laser Science XVII by : Kaoru Yamanouchi
Download or read book Progress in Ultrafast Intense Laser Science XVII written by Kaoru Yamanouchi and published by Springer Nature. This book was released on 2024 with total page 227 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book covers a broad range of interdisciplinary topics, focusing on atoms and molecules in intense laser fields, excitation processes in intense laser fields, photonics and materials, high-order harmonics generation, XFEL, high-power lasers and their applications, and quantum computing. This seventeenth volume features contributions from world-renowned researchers on topics such as applications of attosecond and femtosecond laser pulses, coherence and dynamics in quantum systems, and applications of super-intense laser fields. The PUILS series delivers up-to-date reviews of progress in this 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 of their own subfields of ultrafast intense laser science. Every chapter opens with an overview of the topics to be discussed, so that researchers unfamiliar with the subfield, especially graduate students, can grasp the importance and attractions of the research topic at hand; these are followed by reports of cutting-edge discoveries.
Book Synopsis Progress in Ultrafast Intense Laser Science VII by : Kaoru Yamanouchi
Download or read book Progress in Ultrafast Intense Laser Science VII written by Kaoru Yamanouchi and published by Springer Science & Business Media. This book was released on 2011-05-07 with total page 257 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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 chapters authored by researchers at the forefront of each their own subfields of UILS. Every chapter begins 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 seventh volume covers a broad range of topics from this interdisciplinary research field, focusing on the ionization of atoms and molecules, ultrafast responses of protons and electrons within a molecule, molecular alignment, high-order harmonics and attosecond pulse generation, and acceleration of electrons and ions in laser plasmas.
Book Synopsis Quantum Control of Laser Induced Dynamics of Diatomic Molecular Ions Using Shaped Intense Ultrafast Laser Pulses by : Leigh Graham
Download or read book Quantum Control of Laser Induced Dynamics of Diatomic Molecular Ions Using Shaped Intense Ultrafast Laser Pulses written by Leigh Graham and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Ultrafast Phenomena in Molecular Sciences by : Rebeca de Nalda
Download or read book Ultrafast Phenomena in Molecular Sciences written by Rebeca de Nalda and published by Springer Science & Business Media. This book was released on 2013-10-22 with total page 298 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents the latest developments in Femtosecond Chemistry and Physics for the study of ultrafast photo-induced molecular processes. Molecular systems, from the simplest H2 molecule to polymers or biological macromolecules, constitute central objects of interest for Physics, Chemistry and Biology, and despite the broad range of phenomena that they exhibit, they share some common behaviors. One of the most significant of those is that many of the processes involving chemical transformation (nuclear reorganization, bond breaking, bond making) take place in an extraordinarily short time, in or around the femtosecond temporal scale (1 fs = 10-15 s). A number of experimental approaches - very particularly the developments in the generation and manipulation of ultrashort laser pulses - coupled with theoretical progress, provide the ultrafast scientist with powerful tools to understand matter and its interaction with light, at this spatial and temporal scale. This book is an attempt to reunite some of the state-of-the-art research that is being carried out in the field of ultrafast molecular science, from theoretical developments, through new phenomena induced by intense laser fields, to the latest techniques applied to the study of molecular dynamics.
Book Synopsis Imaging Laser-induced Fragmentation of Molecular Beams, from Positive to Negative Molecules by : Benjamin Berry
Download or read book Imaging Laser-induced Fragmentation of Molecular Beams, from Positive to Negative Molecules written by Benjamin Berry and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The use of ultrafast lasers allows one to study and even control quantum mechanical systems on their natural timescales. Our aim is to study the fragmentation of small molecules in strong laser fields as a means to gain understanding of molecular dynamics and light-matter interactions. Our research group has utilized fast, positively charged molecular ion beams as targets to study and control fragmentation by strong laser fields. This approach allows for detection of all molecular fragments including neutrals, and a coincidence three-dimensional momentum imaging technique is used to characterize the fragmentation. A natural extension of these types of studies is to expand the types of molecular systems that can be studied, from positively charged molecules to neutral and negatively charged molecules. To that end, the primary technical development of this dissertation involved the generation and use of fast, negatively charged molecular beams. Using fast molecular anion beams as targets allows for the study of fragmentation in which all fragments are neutral. As a demonstration, we employ this capability to study F2- dissociation and photodetachment. The dissociation pathways are identified and used to evaluate the initial vibrational population of the F2- beam. The role of dissociation in photodetachment is also explored, and we find that it competes with other dissociative (F+F) and non-dissociative (F2) photodetachment mechanisms. Also highlighted are studies of fragmentation of LiO-, in which the dissociation into Li+O- fragments provides information about the structure of Li O-, including the bond dissociation energy, which was found to be larger than values based on theory. Studies of the autodetachment lifetimes of Li O- were also performed using a pump-probe technique. Additional experimental advancements have made successful pump-probe studies of the ionization of HD+ and Ar2+ possible. Enhancement in the ionization of dissociating HD+ and Ar2+ was observed at surprisingly large internuclear separation where the fragments are expected to behave like separate atoms. The analysis methods used to quantify this enhancement are also described. Finally, the production of excited Rydberg D* fragments from D2 molecules was studied utilizing a state-selective detection method. The carrier-envelope phase dependence of D* formation was found to depend on the range of excited final states of the atomic fragments. We also measured the excited state population of the D* fragments. Together, the studies presented in this work provide new information about fragmentation of positive, negative, and neutral molecules in strong laser fields, and the experimental developments serve as building blocks for future studies that will lead to a better understanding of molecular dynamics.
Book Synopsis Molecular Dynamics in Diatomic Molecules with One- and Two-color Ultrafast Laser Pulses by : Vincent Tagliamonti
Download or read book Molecular Dynamics in Diatomic Molecules with One- and Two-color Ultrafast Laser Pulses written by Vincent Tagliamonti and published by . This book was released on 2014 with total page 182 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Ultrafast Phenomena XIV by : Takayoshi Kobayashi
Download or read book Ultrafast Phenomena XIV written by Takayoshi Kobayashi and published by Springer Science & Business Media. This book was released on 2005-12-28 with total page 914 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume is a collection of papers presented at the Fourteenth International Conference on Ultrafast Phenomena held in Niigata, Japan from July 25-30, 2004. The Ultrafast Phenomena Conferences are held every two years and provide a forum for discussion of the latest results in ultrafast optics and their applications in science and engineering. A total of more than 300 papers were presented, reporting the forefront of research in ultrashort pulse generation and characterization, including new techniques for shortening the duration of laser pulses, for stabilizing their absolute phase, and for improving tenability over broad wavelength ranges, output powers and peak intensities. Ultrafast spectroscopies, particularly time-resolved X-ray and electron diffraction and two-dimensional spectroscopy, continue to give new insights into fundamental processes in physics, chemistry and biology. Control and optimization of the outcome of ultrafast processes represent another important field of research. There are an increasing number of applications of ultrafast methodology in material diagnostics and processing, microscopy and medical imaging. The enthusiasm of the participants, the involvement of many students, the high quality of the papers in both oral and poster sessions made the conference very successful. Many people and organizations made invaluable contributions. The members of the international program committee reviewed the submissions and organized the program. The staff of the Optical Society of America deserves special thanks for making the meeting arrangements and running the meeting smoothly.
Book Synopsis Photoionization and Photo-Induced Processes in Mass Spectrometry by : Ralf Zimmermann
Download or read book Photoionization and Photo-Induced Processes in Mass Spectrometry written by Ralf Zimmermann and published by John Wiley & Sons. This book was released on 2021-07-06 with total page 448 pages. Available in PDF, EPUB and Kindle. Book excerpt: Provides comprehensive coverage of laser-induced ionization processes for mass spectrometry analysis Drawing on the expertise of the leading academic and industrial research groups involved in the development of photoionization methods for mass spectrometry, this reference for analytical scientists covers both the theory and current applications of photo-induced ionization processes. It places widely used techniques such as MALDI side by side with more specialist approaches such as REMPI and RIMS, and discusses leading edge developments in ultrashort laser pulse desorption, to give readers a complete picture of the state of the technology. Photoionization and Photo-Induced Processes in Mass Spectrometry: Fundamentals and Applications starts with a complete overview of the fundamentals of the technique, covering the basics of the gas phase ionization as well as those of laser desorption and ablation, pulse photoionization, and single particle ionization. Numerous application examples from different analytical fields are described that showcase the power and the wide scope of photo ionization in mass spectrometry. -The first general reference book on photoionization techniques for mass spectrometry -Examines technologies and applications of gas phase resonance-enhanced multiphoton ionization mass spectrometry (REMPI-MS) and gas phase resonance ionization mass spectrometry (RIMS) -Provides complete coverage of popular techniques like MALDI -Discusses the current and potential applications of each technology, focusing on process and environmental analysis Photoionization and Photo-Induced Processes in Mass Spectrometry: Fundamentals and Applications is an excellent book for spectroscopists, analytical chemists, photochemists, physical chemists, and laser specialists.
Book Synopsis Progress in Ultrafast Intense Laser Science by : Andreas Becker
Download or read book Progress in Ultrafast Intense Laser Science written by Andreas Becker and published by Springer Science & Business Media. This book was released on 2008-12-16 with total page 276 pages. Available in PDF, EPUB and Kindle. Book excerpt: It is a great pleasure that we are now publishing the fourth volume of the series on PUILS, through which we have been introducing the progress in ultrafast intense laser science, the frontiers of which are rapidly expanding, thanks to the progress in ultrashort and high-power laser technologies. The interdisciplinary nature of this research ?eld is attracting researchers with di?erent expertise and backgrounds. As in the previousvolumeson PUILS, each chapter in the presentvolume, which is in the range of 15–25 pages, begins with an introduction in which a clear and concise account of the signi?cance of the topic is given, followed by a description of the authors’ most recent research results. All the chapters are peer-reviewed. The articles of this fourth volume cover a diverse range of the interdisciplinary research ?eld, and the topics may be grouped into four categories: strong ?eld ionization of atoms (Chaps. 1–2), excitation, ioni- tion and fragmentation of molecules (Chaps. 3–5), nonlinear intense optical phenomena and attosecond pulses (Chaps. 6–8), and laser solid interactions and photoemissions (Chaps. 9–11).
Book Synopsis Imaging Light-induced Molecular Fragmentation Dynamics by : Travis Severt
Download or read book Imaging Light-induced Molecular Fragmentation Dynamics written by Travis Severt and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: When a molecule absorbs energy from its surrounding environment, the molecule's structure begins to evolve. Understanding this evolution at a fundamental level can help researchers, for example, steer chemical reactions to more favorable outcomes. The research reported in this thesis aims to further knowledge about molecular fragmentation dynamics using coincidence three-dimensional momentum imaging. To achieve this goal, we use a combination of ultrafast, intense laser pulses and vacuum-ultraviolet single-photon absorption to initiate and probe molecular dynamics. Specifically, ultrafast lasers allow researchers to follow and control molecular dynamics on their natural time scales. To complement such studies, we also use vacuum-ultraviolet single-photon absorption, in conjunction with the coincidence momentum imaging of all ejected fragments including electrons, to pinpoint state-selective dynamics occurring in various molecular targets. Throughout the thesis, we are interested in several different classes of molecular dynamics. First is the sequential fragmentation of molecules, where two or more bonds break in a step-wise manner. Specifically, we developed the native-frames analysis method, which is used to systematically reduce the dimensionality of multi-body fragmentation using the conjugate momenta of Jacobi coordinates. Applying this framework, we identify the signature of sequential fragmentation and separate its distribution from other competing processes. Moreover, we highlight the method's strengths by following fragmentation dynamics step-by-step and state-selectively using the single-photon double-ionization of D2O as an example. In addition, we explore how the signature of sequential fragmentation within the native-frames method may change under different initial conditions and demonstrate the first steps toward expanding the method to four-body breakup using formic acid as an example. In the future, we hope to identify exotic sequential fragmentation pathways where two or more metastable intermediates are formed together. We also explore molecular isomerization and roaming dynamics leading to bond rearrangement. Specifically, we demonstrate that bond-rearrangement branching ratios in several triatomic molecules are approximately the same order of magnitude. Furthermore, we highlight that the formation of H3 in various alcohol molecules can occur via roaming of H2 molecules. In addition, we study the coherent control of several molecular ions, demonstrating that the CS2+ molecule fragments via a pump-dump mechanism that occurs in a single laser pulse. We also explore the two-color control of D2+ dissociation. Specifically, we observe phase shifts between pathways originating from different initial vibrational levels corresponding to "time-delays" of 10's of attoseconds, showing that such time-scales are not just accessible via electron dynamics. Since single vacuum-ultraviolet photon absorption experiments have proven to be powerful in studying molecular fragmentation dynamics, we investigate the enhancement of lab-based high-order harmonic generation photon sources driven by two-color laser fields. Specifically, we show that two-color 800-400-nm and 800-266-nm driving fields outperform the single-color 800-nm driver by more than an order of magnitude for the plateau harmonics. Furthermore, we demonstrate that the 800-266-nm bichromatic field can control the excursion time of an electron's trajectory by as much as a factor of 2. This result is important for techniques that use the rescattering electron wavepacket as a probe for molecular dynamics, such as in laser-induced electron diffraction (LIED) and high-harmonic spectroscopy (HHS) techniques. Finally, we highlight an upgrade of our coincidence three-dimensional momentum imaging method to measure breakup channels of molecular ions where the fragments have large mass-to-charge ratio differences. Specifically, we detect the light ions, such as H+ and H2+, by adding a second movable offset detector closer to the interaction region. Meanwhile, the heavy ions and neutral fragments fly underneath the new detector and are measured using the original downstream detector, as demonstrated with preliminary CD2+ measurements. In closing, this thesis covers a variety of topics with the common theme of better understanding molecular fragmentation dynamics, ranging from multi-body fragmentation dynamics to isomerization, roaming, and coherent control. In addition, we discuss enhancing high-harmonic-generation-based photon sources to help assist in such studies in the future. Overall, we believe the results presented throughout this thesis contribute to the advancement of molecular dynamics research
Book Synopsis Molecular-frame Measurements of Light-induced Processes Using Rotational Coherences Driven by Ultrafast Laser Pulses by : Huynh Van Sa Lam
Download or read book Molecular-frame Measurements of Light-induced Processes Using Rotational Coherences Driven by Ultrafast Laser Pulses written by Huynh Van Sa Lam and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the main goals of ultrafast atomic, molecular, and optical physics is to monitor and control chemical reactions in real time. Ultrashort laser pulses (time scales in picoseconds or shorter) provide sufficiently high spatio-temporal resolution to study the reaction dynamics. Together with the development of shorter pulses, studies of these reactions in three-dimensional (3D) space are also crucial since the 3D structures determine the physical and chemical properties of molecules. For example, stereoisomers, such as chiral molecules, have the same molecular formula but can behave very differently in reactions with other stereoisomers or optical pulses because of the different orientations of their atoms in space. However, in a gas-phase experiment, the orientation-dependent information is usually lost after averaging over a randomly distributed molecular sample. Many different methods have been investigated to solve this important problem. In 2014, Makhija et al. demonstrated that the angle-dependent strong-field ionization of ethylene (C2H4), an asymmetric top molecule, can be retrieved from a time-resolved measurement of the yield of the cation. In this pump-probe experiment, the pump aligns and the probe ionizes the molecules, and the ion yield is measured as a function of pump-probe delay. The angle dependence is retrieved from fitting to this delay-dependent ion yield. This time-domain approach, called Orientation Resolution through Rotational Coherence Spectroscopy (ORRCS), has many advantages that can be exploited in other applications. The main theme of this work is the further development of ORRCS for extracting orientation-resolved information of different processes from rotational wave packet dynamics. The first goal of this dissertation is to systematically investigate and develop the ORRCS retrieval algorithm, since the retrieval of the angle dependence is sensitive to many parameters. We perform a series of experiments and statistical analyses to evaluate different types of errors, determine the appropriate size of the model, and check the consistency of the retrieval. Specifically, we look at the angle-dependent strong-field ionization of carbon dioxide (CO2, a linear molecule) and sulfur dioxide (SO2, an asymmetric top molecule). Strong-field ionization of CO2 has been discussed extensively in the literature because there were significant discrepancies between different experiments and theories, while SO2 has been used extensively in other experiments. The second goal of this dissertation is to expand the time-domain approach to momentum measurements. With this new development, we present two applications of ORRCS to the dissociation and photoionization of molecules. In the dissociation of molecules, the axial recoil approximation is often used without validation. We show that this approximation can be tested by measuring the momentum distributions of the fragment ions as a function of pump-probe delay. In particular, we examine the dissociation of CO2 and N2 with 800 nm and 262 nm laser pulses, respectively. In each case, we determine how the likelihood of dissociation depends on the initial orientation of the molecule and the effect of the laser field on the momentum distribution of the fragment ions. With a similar framework but different interpretation, we show that substantial information about molecular-frame photoelectron angular distributions can be obtained using rotational wave packets. We retrieve the alignment dependence of photoelectron angular distributions from N2, CO2, and C2H4 in the few-photon ionization regime. We also compare few-photon ionization with single-photon ionization and strong-field ionization to enrich our knowledge in this regime, which is not very well understood. We believe that the time-domain approach discussed in this work is useful in many areas of ultrafast physics and chemistry. With the rapid development of high-repetition-rate light sources in recent years, we expect that many measurements, including those using x-ray free-electron lasers and ultrafast electron beams, will have the ability to apply our method and gain valuable insights into molecular structures and dynamics in the near future.
