Dissertations / Theses on the topic 'Attosecond'
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1
Fieß, Markus. "Advancing attosecond metrology." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-119134.
2
Gagnon, Justin. "Attosecond Electron Spectroscopy." Diss., lmu, 2011. http://nbn-resolving.de/urn:nbn:de:bvb:19-125375.
3
Eckle, Petrissa Roberta. "Attosecond angular streaking /." Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=18118.
4
Lupetti, Mattia. "Plasmonic generation of attosecond pulses and attosecond imaging of surface plasmons." Diss., Ludwig-Maximilians-Universität München, 2015. http://nbn-resolving.de/urn:nbn:de:bvb:19-183678.
Abstract:
Attosecond pulses are ultrashort radiation bursts produced via high
harmonic generation (HHG) during a highly nonlinear excitation process
driven by a near infrared (NIR) laser
pulse. Attosecond pulses can be used
to probe the electron dynamics in ultrafast processes via the attosecond
streaking technique, with a resolution on the
attosecond time scale.
In this thesis it is shown that both the generation of attosecond (AS) pulses
and the probing of ultrafast processes by means of AS pulses, can
be extended to cases in which the respective driving and streaking fields are produced by
surface plasmons excited on nanostructures at NIR wavelengths.
Surface plasmons are optical modes generated by collective oscillations of the surface
electrons in resonance with an external source.
In the first part of this thesis, the idea of high harmonic generation (HHG)
in the enhanced field of a surface plasmon is analyzed in detail by means of numerical simulations.
A NIR pulse is coupled
into a surface plasmon propagating in a hollow core tapered
waveguide filled with noble gas. The plasmon field intensity
increases for decreasing waveguide radius, such that at the apex
the field enhancement is sufficient for producing high harmonic radiation.
It is shown that with this setup it is possible to generate isolated AS pulses
with outstanding spatial and temporal structure, but with an intensity of orders of magnitude smaller than in standard gas harmonic
arrangements.
In the second part, an experimental technique for the imaging
of surface plasmonic excitations on nanostructured surfaces is proposed,
where AS pulses are used to probe the surface field by means of
photoionization. The concept constitutes an
extension of the attosecond streak camera
to ``Attosecond Photoscopy'', which allows
space- and time-resolved imaging of the plasmon dynamics during
the excitation process. It is numerically demonstrated that the relevant parameters of the
plasmonic resonance buildup phase can be determined with subfemtosecond precision.
Finally, the method used for the numerical solution of
the Maxwell's equations is discussed, with
particular attention to the problem of absorbing boundary conditions.
New insights into the mathematical formulation of the absorbing
boundary conditions for Maxwell's equations are provided.Attosekundenpulse sind ultrakurze extrem-ultraviolette (XUV) Pulse, die durch einen nicht-linearen, von einer nah-infraroten (NIR) Laserquelle stimulierten Anregungsprozess erzeugt werden. Attosekundenpulse können verwendet werden, um die Elektronendynamik eines ultraschnellen Prozesses durch die ``Attosecond Streaking'' Technik zu messen, mit einer Auflösung auf der Attosekundenskala. In dieser Dissertation wird gezeigt, dass sowohl die Erzeugung von Attosekundenpulsen als auch die Messung ultraschneller Prozesse mittels Attosekundenpulse auf Fälle erweitert werden können, bei denen die Anregungs- und Streakingsfelder von Oberflächenplasmonen generiert werden, welche bei nahinfraroten Wellenlängen auf Nanostrukturen angeregt werden. Oberflächenplasmonen sind optische Moden, die aus einer kollektiven Schwingung der Elektronen an der Oberfläche in Resonanz mit einer externen Quelle entstehen. Im ersten Abschnitt dieser Dissertation wird das Konzept der High Harmonic Generation (HHG) in plasmonisch erhöhten Feldern durch numerische Simulationen analysiert. Ein NIR Puls wird mit einem Oberflächenplasmon, das sich in einem konischen, mit Edelgas gefüllten, Hohlleiter ausbreitet, gekoppelt. Die Intensität des plasmonischen Feldes steigt mit der Verringerung des Durchmessers des Hohlleiters, sodass die Felderhöhung an seiner Spitze groß genug wird, um hohe harmonische Strahlung zu generieren. Es wird nachgewiesen, dass die Herstellung von isolierten Attosekundenpulsen mit außergewöhnlichen Zeit- und Raumstrukturen möglich ist. Trotzdem ist deren Intensität um mehrere Größenordnungen niedriger als die, die in Experimenten mit fokussierten Laserpulsen erreicht werden kann. Im zweiten Abschnitt wird eine experimentelle Technik für die Abbildung plasmonischer Oberflächenanregungen vorgeschlagen, wobei Attosekundenpulse verwendet werden, um das Feld an der Oberfläche mittels ``Momentum Streaking'' der photoionisierten Elektronen zu messen. Dieses Konzept ist eine Erweiterung der ``Attosecond Streak Camera'', welches ich ``Attosecond Photoscopy'' nenne. Es ermöglicht die Abbildung eines Plasmons in Zeit und Raum während des Anregungsprozesses. Anhand von numerischen Simulationen wird es gezeigt, dass die wesentlichen Parameter des plasmonischen Resonanzaufbaus mit subfemtosekunden-Präzision bestimmt werden können. Zuletzt wird die Methode für die numerische Lösung der Maxwell-Gleichungen diskutiert, mit Fokus auf das Problem der absorbierenden Randbedingungen. Neue Einsichten in die mathematische Formulierung der Randbedingungen der Maxwell-Gleichungen werden vorgestellt.
5
Flögel, Martin [Verfasser]. "Raising the XUV Intensity towards Attosecond-Attosecond Pump-Probe Experiments / Martin Flögel." Berlin : Freie Universität Berlin, 2017. http://d-nb.info/1133492347/34.
6
Wirth, Adrian. "Attosecond transient absorption spectroscopy." Diss., lmu, 2011. http://nbn-resolving.de/urn:nbn:de:bvb:19-140120.
7
Chirla, Razvan Cristian. "Attosecond Pulse Generation and Characterization." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1313429461.
8
Hageman, Stephen James. "Complex Attosecond Transient-absorption Spectroscopy." The Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1608050018545904.
9
Schapper, Florian. "Attosecond structure of high-order harmonics." Konstanz Hartung-Gorre, 2010. http://d-nb.info/1000540448/04.
10
Wu, Yi. "High flux isolated attosecond pulse generation." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6038.
Abstract:
This thesis outlines the high intensity tabletop attosecond extreme ultraviolet laser source at the Institute for the Frontier of Attosecond Science and Technology Laboratory.
First, a unique Ti:Sapphire chirped pulse amplifier laser system that delivers 14 fs pulses with 300 mJ energy at a 10 Hz repetition rate was designed and built. The broadband spectrum extending from 700 nm to 900 nm was obtained by seeding a two stage Ti:Sapphire chirped pulse power amplifier with mJ-level white light pulses from a gas filled hollow core fiber. It is the highest energy level ever achieved by a broadband pulse in a chirped pulse amplifier up to the current date.
Second, using this laser as a driving laser source, the generalized double optical gating method is employed to generate isolated attosecond pulses. Detailed gate width analysis of the ellipticity dependent pulse were performed. Calculation of electron light interaction dynamics on the atomic level was carried out to demonstrate the mechanism of isolated pulse generation.
Third, a complete diagnostic apparatus was built to extract and analyze the generated attosecond pulse in spectral domain. The result confirms that an extreme ultraviolet super continuum supporting 230 as isolated attosecond pulses at 35 eV was generated using the generalized double optical gating technique. The extreme ultraviolet pulse energy was ~100 nJ at the exit of the argon gas target.Ph.D.
Doctorate
Optics and Photonics
Optics and Photonics
Optics
11
Diveki, Zsolt. "Generation and Application of Attosecond Pulses." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00722473.
Abstract:
To capture electronic rearrangements inside a molecule or during chemical reactions, attosecond (as, 1 as =10−18 s) time resolution is needed. To create a light pulse with this duration, the central frequency has to be in the XUV range and cover several tens of eVs. Moreover, the frequency components have to be synchronized. The so called High Harmonic Generation (HHG) in gases well suits this task. During this process a high intensity laser pulse is focused in a gas jet, where its electric field bends the potential barrier of an atom allowing an electron wave packet (EWP) to tunnel ionize. Following the electric field of the laser the EWP gets accelerated, gaining a large kinetic energy that may be released as a high energy (XUV) photon in the event of a re-collision with the ionic core. These recolliding EWP probe the structure and dynamics of the core in a self-probing scheme: the EWP, that is emitted by the molecule at a certain time, probes itself later. More precisely, this "self-probing" scheme gives access to the complex valued recombination dipole moment (RDM) of the molecule which is determined by both the nuclear and electronic structure. The recombination encodes these characteristics into the spectral amplitude, phase and polarization state of the harmonic radiation emitted by the dipole. Due to the coherent nature of HHG it is possible to measure all these three parameters. Moreover, it is in principle possible through a tomographic procedure to reconstruct the radiating orbital.The objective of my thesis was two-fold. By implementing advanced characterization techniques of the harmonic amplitude, phase and polarization we studied i) the electronic structure of N2 and laser induced multi-channel tunnel ionization. We presented the reconstruction of molecular orbitals and revealed the ionization channel dependent ultrafast nuclear vibration. We also studied ii) the reflectivity and dispersion of recently designed chirped XUV mirrors that can shape the temporal profile of attosecond pulses. With these mirrors we could control the spectral phase over 20 eV and compensate the GDD of the harmonics or introduce a TOD. We also proposed a novel attosecond pulse shaper.
12
Wu, Xiuyu. "Optimization of Intense Attosecond XUV Pulses." Thesis, Umeå universitet, Institutionen för fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-165569.
Abstract:
To observe electron dynamics in molecules and atoms which takes place on the attosecond timescale, single isolated attosecond pulses are required utilized in performing pump–probe experiments. The Light Wave Synthesizer 20 generates intense sub-5 fs pulses with a peak power of 16 TW and a broad spectrum. This offers a chance of generating isolated attosecond pulses via high harmonic generation (HHG) in gas medium. In this project, the variation of cutoff energy of HHG with different intensities of the driving laser was investigated. In addition, an isolated attosecond pulse with an Fourier-limited pulse duration of 188 as is produced with a selection of 15 eV around the cutoff region. Moreover, one optimization method refer to GDD scan was illustrated to optimize the HHG cutoff and continuum.
13
Wang, He. "From few-cycle femtosecond pulse to single attosecond pulse-controlling and tracking electron dynamics with attosecond precision." Diss., Kansas State University, 2010. http://hdl.handle.net/2097/4393.
Abstract:
Doctor of PhilosophyDepartment of Physics
Zenghu Chang
The few-cycle femtosecond laser pulse has proved itself to be a powerful tool for controlling the electron dynamics inside atoms and molecules. By applying such few-cycle pulses as a driving field, single isolated attosecond pulses can be produced through the high-order harmonic generation process, which provide a novel tool for capturing the real time electron motion. The first part of the thesis is devoted to the state of the art few-cycle near infrared (NIR) laser pulse development, which includes absolute phase control (carrier-envelope phase stabilization), amplitude control (power stabilization), and relative phase control (pulse compression and shaping). Then the double optical gating (DOG) method for generating single attosecond pulses and the attosecond streaking experiment for characterizing such pulses are presented. Various experimental limitations in the attosecond streaking measurement are illustrated through simulation. Finally by using the single attosecond pulses generated by DOG, an attosecond transient absorption experiment is performed to study the autoionization process of argon. When the delay between a few-cycle NIR pulse and a single attosecond XUV pulse is scanned, the Fano resonance shapes of the argon autoionizing states are modified by the NIR pulse, which shows the direct observation and control of electron-electron correlation in the temporal domain.
14
Kiesewetter, Dietrich. "Dynamics of Near-Threshold, Attosecond Electron Wavepackets in Strong Laser Fields." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1544447128975478.
15
Hassan, Mohammed. "Synthesis and control of attosecond light transients." Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-161230.
16
Chini, Michael. "Characterization and Application of Isolated Attosecond Pulses." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5163.
Abstract:
Tracking and controlling the dynamic evolution of matter under the influence of external fields is among the most fundamental goals of physics. In the microcosm, the motion of electrons follows the laws of quantum mechanics and evolves on the timescale set by the atomic unit of time, 24 attoseconds. While only a few time-dependent quantum mechanical systems can be solved theoretically, recent advances in the generation, characterization, and application of isolated attosecond pulses and few-cycle femtosecond lasers have given experimentalists the necessary tools for dynamic measurements on these systems. However, pioneering studies in attosecond science have so far been limited to the measurement of free electron dynamics, which can in most cases be described approximately using classical mechanics. Novel tools and techniques for studying bound states of matter are therefore desired to test the available theoretical models and to enrich our understanding of the quantum world on as-yet unprecedented timescales. In this work, attosecond transient absorption spectroscopy with ultrabroadband attosecond pulses is presented as a technique for direct measurement of electron dynamics in quantum systems, demonstrating for the first time that the attosecond transient absorption technique allows for state-resolved and simultaneous measurement of bound and continuum state dynamics. The helium atom is the primary target of the presented studies, owing to its accessibility to theoretical modeling with both ab initio simulations and to model systems with reduced dimensionality. In these studies, ultrafast dynamics - on timescales shorter than the laser cycle - are observed in prototypical quantum mechanical processes such as the AC Stark and ponderomotive energy level shifts, Rabi oscillations and electromagnetically-induced absorption and transparency, and two-color multi-photon absorption to "dark" states of the atom. These features are observed in both bound states and quasi-bound autoionizing states of the atom. Furthermore, dynamic interference oscillations, corresponding to quantum path interferences involving bound and free electronic states of the atom, are observed for the first time in an optical measurement. These first experiments demonstrate the applicability of attosecond transient absorption spectroscopy with ultrabroadband attosecond pulses to the study and control of electron dynamics in quantum mechanical systems with high fidelity and state selectivity. The technique is therefore ideally suited for the study of charge transfer and collective electron motion in more complex systems. The transient absorption studies on atomic bound states require ultrabroadband attosecond pulses ? attosecond pulses with large spectral bandwidth compared to their central frequency. This is due to the fact that the bound states in which we are interested lie only 15-25 eV above the ground state, so the central frequency of the pulse should lie in this range. On the other hand, the bandwidth needed to generate an isolated 100 as pulse exceeds 18 eV - comparable to or even larger than the central frequency. However, current methods for characterizing attosecond pulses require that the attosecond pulse spectrum bandwidth is small compared to its central frequency, known as the central momentum approximation. We therefore explore the limits of attosecond pulse characterization using the current technology and propose a novel method for characterizing ultrabroadband attosecond pules, which we term PROOF (phase retrieval by omega oscillation filtering). We demonstrate the PROOF technique with both simulated and experimental data, culminating in the characterization of a world-record-breaking 67 as pulse.Ph.D.
Doctorate
Physics
Sciences
Physics
17
Bhardwaj, Siddharth. "Modeling generation and characterization of attosecond pulses." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91127.
Abstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2014.93
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 135-142).
Generation of high-order harmonics has emerged as a powerful technique for the generation of broadband coherent radiation in the EUV regime. This has lead to the development of table-top EUV sources that can produce attosecond pulses. These pulses can serve as a probe to resolve atomic attosecond dynamics and image atomic orbitals and molecular motion. Due to high spatial and temporal coherence, high-order harmonic radiation can also be used to seed free electron lasers, which allow the generation of high-intensity X-ray radiation that can be used for imaging biomolecules. Since the first observation of high-order harmonics, effort has been made to accurately model both the generation and the characterization of attosecond pulses. Work on the modeling of high harmonic generation can be divided into two parts: (a) description of the interaction between the JR pulse and atoms that leads to emission of attosecond pulses (the single atom response) and (b) modeling of the propagation of attosecond pulses by accounting for macroscopic phase matching effects. In this work, we will focus on the single atom response which can be calculated either by numerically solving the time dependent Schrodinger equation (TDSE) or through the semi-classical three step model (TSM). In Chapter 2, the theory of light-atom interaction will be reviewed with the focus on the calculation of the dipole trasition matrix element (DTME) in the strong field formalism. It will be shown that the choice of the basis states - Volkov states and Coulomb Volkov states - to describe electrons in the continuum is crucial to the accuracy of DTME calculation. In Chapter 3, the TSM will be derived from the Schrodinger equation by using the saddle point approximation. Through this derivation, the quantum mechanical laser-atom interaction is reduced to a semi-classical model comprising of ionization, propagation and recombination . The numerical scheme for solving the TDSE will be discussed. It will then be used to demonstrate the generation of isolated attosecond pulses from non-sinusoidal sub-cycle pulses. The results of ADK and non-adiabatic ionization models will be compared with that from numerical TDSE, and then used to calculate the harmonic spectra in the tunneling and multi-photon ionization regimes. The recombination step of the TSM, which plays a crucial role in determining the qualitative shape of the high-order harmonic spectrum, will be investigated in Chapter 4. A commonly observed feature of Argon's high-order harmonic spectrum is the presence of a minimum at around 50 eV called the Cooper minimum. The minimum in the high-order harmonic spectrum has been attributed to the minimum in the recombination amplitude. The recombination amplitude will be calculated - in the strong field formalism - using length and acceleration form for two choices of continuum electron wavefunction description (Volkov and Coulomb-Volkov). Attosecond pulse characterization techniques, which are an extension of the subpicosecond pulse characterization technique like FROG and SPIDER, rely on the photoionization process to transfer the amplitude and phase information of the attosecond pulse to the photoelectron spectrum. For accurate pulse characterization, it is crucial to model the photoionization process accurately. Since photoionization and recombination are reverse processes, the improvements in the calculation of the recombination amplitude in Chapter 4, can be used to improve the model function of the pulse retrieval algorithm. It will be shown that the proposed improvements are crucial for accurate characterization of low energy EUV pulses.
by Siddharth Bhardwaj.
Ph. D.
18
Simpson, Emma. "Attosecond transient absorption spectroscopy in atomic species." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/44970.
Abstract:
When high intensity laser light is focused into a gaseous target, high energy photons can be produced through the strongly nonlinear effect of high order harmonic generation. For a 30 fs, 800 nm or 1400 nm wavelength laser pulse, the result is a train of attosecond pulses produced at odd harmonic frequencies of the driving laser field, spanning energy ranges into the 100s eV. These attosecond pulses can access timescales characteristic to the movement of electrons in atoms, and by exploiting their properties as an ultrafast probe, electron dynamics in evolving atomic systems can be observed. This thesis presents the development of a pump-probe beamline capable of performing transient absorption spectroscopy experiments with resolution better than 150 as. Accompanying a full description of the experimental setup and methods, investigations are made into the attosecond transient absorption from strong field dressed helium and krypton atoms around their first ionisation edge, and 3d ionisation edge respectively. The result of the delay dependent transient absorption measurement is modulations to the recorded absorption amplitude for the harmonic orders around the respective ionisation thresholds. We investigated intensity regimes with an 800 nm laser field approaching the strong field ionisation threshold in helium. Experimental results are presented considering first the response of strong field dressed helium using an 800 nm laser field, and second the response of strong field dressed helium and krypton using a 1400 nm laser field. The use of the longer 1400 nm wavelength allows access to higher energy probe harmonics, enabling laser dressed krypton core to continuum, and core to Rydberg state transitions to be studied. By comparing the effect to the delay dependent absorption modulation as additional parameters are varied, information can be gained about the behaviour of the electrons. The parameters studied as a function of delay include: the dressing field intensity, target backing pressure and dressing field relative linear polarisation, aligned both parallel and perpendicular with respect to the probing harmonic pulse train. Key results include a strong suppression of the modulation amplitude for the above ionisation threshold harmonic orders when the dressing field linear polarisation is changed from parallel to perpendicular in the helium target. This is reproduced at both 800 nm and 1400 nm driving wavelengths.
19
Khan, Sabih ud Din. "Generation of short and intense attosecond pulses." Diss., Kansas State University, 2012. http://hdl.handle.net/2097/13521.
Abstract:
Doctor of PhilosophyDepartment of Physics
Brett DePaola
Zenghu Chang
Extremely broad bandwidth attosecond pulses (which can support 16as pulses) have been demonstrated in our lab based on spectral measurements, however, compensation of intrinsic chirp and their characterization has been a major bottleneck. In this work, we developed an attosecond streak camera using a multi-layer Mo/Si mirror (bandwidth can support ~100as pulses) and position sensitive time-of-flight detector, and the shortest measured pulse was 107.5as using DOG, which is close to the mirror bandwidth. We also developed a PCGPA based FROG-CRAB algorithm to characterize such short pulses, however, it uses the central momentum approximation and cannot be used for ultra-broad bandwidth pulses. To facilitate the characterization of such pulses, we developed PROOF using Fourier filtering and an evolutionary algorithm. We have demonstrated the characterization of pulses with a bandwidth corresponding to ~20as using synthetic data. We also for the first time demonstrated single attosecond pulses (SAP) generated using GDOG with a narrow gate width from a multi-cycle driving laser without CE-phase lock, which opens the possibility of scaling attosecond photon flux by extending the technique to peta-watt class lasers. Further, we generated intense attosecond pulse trains (APT) from laser ablated carbon plasmas and demonstrated ~9.5 times more intense pulses as compared to those from argon gas and for the first time demonstrated a broad continuum from a carbon plasma using DOG. Additionally, we demonstrated ~100 times enhancement in APT from gases by switching to 400 nm (blue) driving pulses instead of 800 nm (red) pulses. We measured the ellipticity dependence of high harmonics from blue pulses in argon, neon and helium, and developed a simple theoretical model to numerically calculate the ellipticity dependence with good agreement with experiments. Based on the ellipticity dependence, we proposed a new scheme of blue GDOG which we predict can be employed to extract intense SAP from an APT driven by blue laser pulses. We also demonstrated compression of long blue pulses into >240 µJ broad-bandwidth pulses using neon filled hollow core fiber, which is the highest reported pulse energy of short blue pulses. However, compression of phase using chirp mirrors is still a technical challenge.
20
Wei, Hui. "Characterization and application of isolated attosecond pulses." Diss., Kansas State University, 2017. http://hdl.handle.net/2097/35373.
Abstract:
Doctor of PhilosophyDepartment of Physics
Chii-Dong Lin
Isolated attosecond pulse (IAP) is a tool of probing electronic dynamics occurring in atoms, molecules, clusters and solids, since the time scale of electronic motion is on the order of attoseconds. The generation, characterization and applications of IAPs has become one of the fast frontiers of laser experiments. This dissertation focuses on several aspects of attosecond physics. First, we study the driving wavelength scaling of the yield of high-order harmonic generation (HHG) by applying the quantum orbit theory. The unfavorable scaling law especially for the short quantum orbit is of great importance to attoseond pulse generation toward hundreds of eVs or keV photon energy region by mid-infrared (mid-IR) lasers. Second, we investigate the accuracy of the current frequency-resolved optical gating for complete reconstruction of attosecond bursts (FROG-CRAB) and phase retrieval by omega oscillation filtering (PROOF) methods for IAP characterization by simulating the experimental data by theoretical calculation. This calibration is critical but has not been carefully carried out before. We also present an improved method, namely the swPROOF which is more universal and robust than the original PROOF method. Third, we investigate the controversial topic of photoionization time delay. We find the limitation of the FROG-CRAB method which has been used to extract the photoionization time delay between the 2s and 2p channels in neon. The time delay retrieval is sensitive to the attochirp of the XUV pulse, which may lead to discrepancies between experiment and theory. A new fitting method is proposed in order to overcome the limitations of FROG-CRAB. Finally, IAPs are used to probe the dynamic of electron correlation in helium atom by means of attosecond transient absorption spectroscopy. The agreement between the measurement and our analytical model verifies the observation of time-dependent build up of the 2s2p Fano resonance.
21
Maroju, Praveen Kumar [Verfasser], and Giuseppe [Akademischer Betreuer] Sansone. "Attosecond pulse shaping at a seeded free-electron laser : : towards attosecond time-resolved experiments at the free-electron lasers." Freiburg : Universität, 2021. http://d-nb.info/1239556527/34.
22
Goulielmakis, Eleftherios. "Complete Characterization of Light Waves using Attosecond Pulses." Diss., lmu, 2005. http://nbn-resolving.de/urn:nbn:de:bvb:19-41112.
23
Magerl, Elisabeth. "Attosecond photoelectron spectroscopy of electron transport in solids." Diss., lmu, 2011. http://nbn-resolving.de/urn:nbn:de:bvb:19-130576.
24
Hirisave, Shivaram Niranjan. "Attosecond Resolved Electron Wave Packet Dynamics in Helium." Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/293618.
Abstract:
Electron dynamics in atoms and molecules occurs on a time-scale of attoseconds (10⁻¹⁸s). With the availability of strong field (∼ 10¹²- 10¹³ W cm⁻²) femtosecond (10⁻¹⁵s) laser pulses with electric fields that can reach and exceed the Coulomb field strength experienced by an electron in the ground state of an atom, it is now possible to generate even shorter pulses with durations on the order of attoseconds by the process of high-harmonic generation (HHG). In this dissertation, experiments to study electron dynamics on attosecond time-scales in a helium atom using attosecond pulses generated by HHG will be described. We use extreme-ultraviolet (XUV) attosecond pulse trains and strong femtosecond near-infrared (IR) laser pulses to excite and ionize helium atoms. We first discuss an experimental technique that allows us to quantify and reduce the detrimental effects of Gouy phase slip on attosecond XUV-IR experiments. We then discuss our experiments to study the dynamic behavior of electronic states in a strong field modified helium atom where we use attosecond pulses to explore the strong-field modified atomic landscape. Using the Floquet theory to interpret our experimental observations we measure the variation in quantum phase of interferences between different fourier components of Floquet states as the IR intensity is varied and as different ionization channels dominate, in real-time. Next, we briefly discuss quantum interferences between photo-electrons ionized from XUV excited states in helium using an IR field which is polarized orthogonal to the XUV polarization. We observe variation in angular distribution of photo-electrons as a function of XUV-IR time-delay. We then discuss a new technique to measure the time-of-birth of attosecond pulses using XUV+IR photo-ionization in helium as a measurement probe. Finally, experiments to study the evolution of XUV excited wave-packets in helium on a time-scale of 100's of femtoseconds with attosecond resolution will be described.
25
Rybka, Tobias [Verfasser]. "Attosecond Electron Transport in Plasmonic Nanostructures / Tobias Rybka." Konstanz : Bibliothek der Universität Konstanz, 2019. http://d-nb.info/117697193X/34.
26
Neidel, Christian [Verfasser]. "Attosecond time-resolved experiments - towards biomolecules / Christian Neidel." Berlin : Freie Universität Berlin, 2017. http://d-nb.info/1177374161/34.
27
Haessler, Stefan. "Generation of attosecond pulses in atoms and molecules." Paris 11, 2009. http://www.theses.fr/2009PA112224.
Abstract:
Dans plusieurs expériences, nous démontrons le potentiel du processus de génération d’harmoniques d’ordre élevé pour observer des dynamiques électroniques et nucléaires intra-moléculaires ultrarapides. La plus grande partie de cette thèse traite d'expériences où les molécules constituent le milieu de génération et le paquet d'ondes électronique recollisionnant joue le rôle d'une `auto-sonde'. Les mesures de phase et amplitude de l’émission harmonique des molécules de CO2 et N2 alignées dans le référentiel du laboratoire nous permettent d’extraire l’élément de matrice du dipole de recombinaison. Ce dernier contient la signature d’une interférence quantique entre les parties libre et liée de la fonction d’onde électronique totale. L’utilisation de cette interférence quantique pour la mise-en-forme de l’émission XUV attoseconde (1as=10−18s) sera démontrée. De plus, nous étudions théoriquement la tomographie d’orbitales moléculaires à partir des éléments de matrice du dipole de recombinaison et nous démontrons sa faisabilité expérimentale. Ceci ouvre la perspective d’imager les distorsions ultra-rapides d’une orbitale frontière lors d’une réaction chimique. Dans une deuxième partie de cette thèse, nous utilisons la lumière XUV cohérente émise par des atomes d’argon pour photoioniser des molécules de N2 et mesurons comment une résonance auto-ionisante modifie la phase spectrale du paquet d’ondes de photoélectrons émis. Le dernier chapitre de ce manuscrit décrit des études de génération d’impulsions XUV attosecondes dans un milieu différent: des plasmas d’ablation. La première caractérisation temporelle d’une telle source démontre sa structure femtoseconde et attosecondeIn several experiments, we demonstrate the potential of the process of high-order harmonic generation for observing ultrafast intra-molecular electron and nuclear dynamics. The largest part of this thesis treats experiments where molecules constitute the generating medium and the recolliding electron wavepacket takes the role of a ‘self-probe’. Measurements of phase and amplitude of the harmonic emission from CO2 and N2 molecules aligned in the laboratory frame allow us to extract the recombination dipole matrix element. The latter contains the signature of quantum interference between the free and bound parts of the total electronic wavefunction. The utilization of this interference for the shaping of the attosecond (1as=10−18s) XUV emission is demonstrated. Furthermore, we study theoretically molecular orbital tomography from the recombination dipole matrix elements and demonstrate its experimental feasibility. This opens the perspective of imaging ultrafast distortions of a frontier orbital during a chemical reaction. In a second part of this thesis, we use the coherent XUV light emitted by argon atoms to photoionize N2 molecules and measure how an auto-ionizing resonance modifies the spectral phase of the ejected photoelectron wavepacket. The last chapter of this thesis describes studies of the generation of XUV attosecond pulses in a different medium: ablation plasmas. The first temporal characterization of such a source demonstrates its femtosecond and attosecond structure
28
Wu, Xiuyu. "Generation and characterization of intense attosecond XUV pulses." Thesis, Umeå universitet, Institutionen för fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-165564.
Abstract:
Electronic dynamics in molecules and atoms takes place on the attosecond timescale. For the observation of such processes, measurement techniques with attosecond resolution are needed. High-harmonic generation (HHG) in gas medium provides an ultrashort light source on the attosecond timescale for observing, understanding and controlling light-induced process on this scale with the necessary time resolution. To be able to use these attosecond pulses to measure electron dynamics, they have to be characterized. For this characterization, the XUV spectrum is extremely important. The XUV spectrum not only contains the information about the photon energies of the pulses, but also temporal information such as the difference between a single isolated attosecond pulse or an attosecond pulse train. The Light Wave Synthesizer 20 generates intense femtosecond pulses with a peak power of 16 TW and a spectrum spanning over the region from 580 to 1000 nm. This allow one to generate attosecond pulses based on HHG in gas medium with 100 eV photon energy and up to 20 nJ pulse energy. The generated attosecond pulses can be observed with a photodiode to measure the energy, an XUV CCD used as a profiler and an XUV flat-field spectrometer. The detector of the flat-field spectrometer is an XUV CCD which records the diffracted beam from a grating. Hence, a certain pixel of the camera shows the intensity for a certain range of photon energies. However, the calibration from pixel to energy is not always fixed due to e.g. the alignment of the spectrometer. This pixel to photon energy calibration can be done either by using the harmonic peaks in the XUV spectra or theoretical analyses of the spectrometer structure. In this thesis, both methods are investigated and the results are in good agreement. Due to the analytical calibration has a lower error and faster to do, future measurements can be evaluated with the analytical method.
29
Smith, Gregory J. "Application of Attosecond Techniques to Condensed Matter Systems." The Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1608496995249541.
30
Alexandridi, Christina-Anastasia. "Attosecond spectroscopy : study of the photoionization dynamics of atomic gases close to resonances." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS571/document.
Abstract:
L'interaction des puissantes impulsions laser avec les gaz atomiques et moléculaires entraîne l’émission de flashs exceptionnellement brefs de lumière XUV grâce au processus de génération harmonique d'ordre élevé (GHOE) de la fréquence laser fondamentale. Ce rayonnement ultra-bref, dans la gamme attoseconde (10⁻¹⁸ s), permet des investigations détaillées de la dynamique électronique ultra-rapide dans la matière. Le travail de cette thèse consiste à étudier les délais de photoionisation au voisinage de différents types de résonances, en utilisant la technique Rainbow RABBIT. Il s'agit d'une technique interférométrique à deux couleurs (XUV + IR) qui permet d'accéder au temps nécessaire à l'électron pour s'échapper du potentiel atomique avec une haute résolution. Nous nous intéressons particulièrement à deux cas: i) les résonances auto-ionisantes spectralement étroites (dizaines de meV) et ii) les minima de type Cooper ayant une largeur spectrale de quelques eV. L'effet de ces structures de continuum sur la dynamique d'ionisation correspondante est étudiéThe interaction of intense laser pulses with atomic and molecular gases results in exceptionally short bursts of XUV light, through the process of high-order harmonic generation of the fundamental laser frequency. This ultrashort radiation, in the attosecond (10⁻¹⁸ s) range, allows detailed investigations of ultrafast electron dynamics in matter. The work of this thesis consists in studying the photoionization delays close to different types of resonances, using the Rainbow RABBIT technique. This is a two-color interferometric technique (XUV + IR) that allows access to the time required for the electron to escape the atomic potential with high resolution. We are particularly interested in two cases: i) autoionizing resonances which are spectrally narrow (tens of meV) and ii) Cooper-type minima which have a spectral width of some eV. The effect of these continuum structures on the corresponding ionization dynamics is studied
31
Bocoum, Maïmouna. "Harmonic and electron generation from laser-driven plasma mirrors." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX023/document.
Abstract:
Dans cette thèse expérimentale, nous nous intéressons à la réponse non-linéaire d’un miroir plasma sous l’influence d’un laser d’intensité sous-relativiste (~10^18 W/cm^2), et de très courte durée (~30fs). Nous avons en particulier étudié la génération d’impulsions attosecondes (1as=10^(-18) s) et de faisceaux d’électrons en effectuant des expériences dites de « pompe-sonde » contrôlées. Un premier résultat important est l’observation d’une anti-corrélation entre l’émission X-UV attoseconde et l’accélération d’électron lorsque l’on change la longueur caractéristique du plasma, résultats confirmés par des simulations numériques. Un second résultat important concerne le diagnostique de l’expansion du plasma sous vide par « interférométrie en domaine spatial » (SDI), technique élaborée dans le cadre de cette thèse. Enfin nous discutons à deux reprises l’utilisation d’algorithmes de reconstruction de phase dans le domaine spatiale ou temporel.De manière plus générale, nous avons cherché à replacer ce travail de thèse dans un contexte scientifique plus général. En particulier, nous tentons de convaincre le lecteur qu’à travers l’intéraction laser-miroir plasma, il devient concevable de fournir un jour aux utilisateurs des sources peu onéreuses d’impulsions X-UV et de faisceaux d’électrons de résolutions temporelles inégaléesThe experimental work presented in this manuscript focuses on the non-linear response of plasma mirrors when driven by a sub-relativistic (~10^18 W/cm^2) ultra-short (~30fs) laser pulse. In particular, we studied the generation of attosecond pulses (1as=10^(-18) s) and electron beams from plasma mirror generated in controlled pump-probe experiment. One first important result exposed in this manuscript is the experimental observation of the anticorrelated emission behavior between high-order harmonics and electron beams with respect to plasma scale length. The second important result is the presentation of the « spatial domain interferometry » (SDI) diagnostic, developed during this PhD to measure the plasma expansion in vacuum. Finally, we will discuss the implementation of phase retrieval algorithms for both spatial and temporal phase reconstructions.From a more general point of view, we replace this PhD in its historical context. We hope to convince the reader that through laser-plasma mirror interaction schemes, we could tomorrow conceive cost-efficient X-UV and energetic electron sources with unprecedented temporal resolutions
32
Lupetti, Mattia [Verfasser], and Armin [Akademischer Betreuer] Scrinzi. "Plasmonic generation of attosecond pulses and attosecond imaging of surface plasmons : modeling and simulation of experimental proposals / Mattia Lupetti. Betreuer: Armin Scrinzi." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2015. http://d-nb.info/1073826090/34.
33
Burzo, Andrea Mihaela. "Improved control of single cycle pulse generation by molecular modulation." Texas A&M University, 2005. http://hdl.handle.net/1969.1/5010.
Abstract:
Generation of reproducible attosecond (10-18s) pulses is an exciting goal: in the
same way as femtosecond pulses were used to make "movies" of the atomic motion
in molecules, attosecond pulses could "uncover" the motion of electrons around nuclei.
In this dissertation, we have suggested new ideas that will allow improving one
scheme for obtaining such ultra-short pulses: the molecular modulation technique. In
a theoretical proposal called Raman Additive technique, we have suggested a method
that will allow (with a proper phase stabilization of generated sidebands) to obtain
reproducible waveforms of arbitrary shape. An exciting range of possibilities could
open up - not only for absolute phase control or sub-cycle shape control, but also for
investigation of multiphoton ionization rates as a function of the sub-cycle shape. We
have elaborated on the latter subject in another theoretical project, where we have
exploited the unique feature of such ultrashort laser pulses, which is synchronization
with molecular motion (rotational or vibrational), in order to investigate photoionization
of molecules. From experimental point of view, a different construction of driving
lasers than previously employed led to establishment of larger molecular coherences
at higher operating pressure than in previous experiments. This resulted in simultaneous
generation of rotational and vibrational sidebands with only two fields applied.
In another experimental proposal using rotational transition in deuterium we have shown that employing a hollow waveguide instead of normal Raman cell improves
the efficiency of the generation process. By optimizing gas pressure and waveguide
geometry to compensate the dispersion, the method can be extended to efficiently
generate Raman sidebands at a much lower energy of driving fields than previously
employed. At the end, a very exciting possibility for controlling the molecular motion
in a Raman driven system will be shown. Based on the interference effects (EITlike)
that take place inside of a molecule, selectivity of different degrees of freedom
can be achieved (for example switching from rotational-vibrational motion to pure
rotational).
34
Wirth, Adrian [Verfasser], and Ferenc [Akademischer Betreuer] Krausz. "Attosecond transient absorption spectroscopy / Adrian Wirth. Betreuer: Ferenc Krausz." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2011. http://d-nb.info/1019930233/34.
35
Krüger, Michael. "Attosecond physics in strong-field photoemission from metal nanotips." Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-162459.
36
Ghimire, Shambhu. "Study on generation of attosecond pulse with polarization gating." Diss., Manhattan, Kan. : Kansas State University, 2007. http://hdl.handle.net/2097/283.
37
Zhang, Qi. "Generation and characterization of sub-70 isolated attosecond pulses." Doctoral diss., University of Central Florida, 2014. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6391.
Abstract:
Dynamics occurring on microscopic scales, such as electronic motion inside atoms and molecules, are governed by quantum mechanics. However, the Schroedinger equation is usually too complicated to solve analytically for systems other than the hydrogen atom. Even for some simple atoms such as helium, it still takes months to do a full numerical analysis. Therefore, practical problems are often solved only after simplification. The results are then compared with the experimental outcome in both the spectral and temporal domain. For accurate experimental comparison, temporal resolution on the attosecond scale is required. This had not been achieved until the first demonstration of the single attosecond pulse in 2001. After this breakthrough, "attophysics" immediately became a hot field in the physics and optics community.
While the attosecond pulse has served as an irreplaceable tool in many fundamental research studies of ultrafast dynamics, the pulse generation process itself is an interesting topic in the ultrafast field. When an intense femtosecond laser is tightly focused on a gaseous target, electrons inside the neutral atoms are ripped away through tunneling ionization. Under certain circumstances, the electrons are able to reunite with the parent ions and release photon bursts lasting only tens to hundreds of attoseconds. This process repeats itself every half cycle of the driving pulse, generating a train of single attosecond pulses which lasts longer than one femtosecond. To achieve true temporal resolution on the attosecond time scale, single isolated attosecond pulses are required, meaning only one attosecond pulse can be produced per driving pulse.
Up to now, there are only a few methods which have been demonstrated experimentally to generate isolated attosecond pulses. Pioneering work generated single attosecond pulse using a carrier-envelope phase-stabilized 3.3 fs laser pulse, which is out of reach for most research groups. An alternative method termed as polarization gating generated single attosecond pulses with 5 fs driving pulses, which is still difficult to achieve experimentally. Most recently, a new technique termed as Double Optical Gating (DOG) was developed in our group to allow the generation of single attosecond pulse with longer driving pulse durations. For example, isolated 150 as pulses were demonstrated with a 25 fs driving laser directly from a commercially-available Ti:Sapphire amplifier. Isolated attosecond pulses as short as 107 as have been demonstrated with the DOG scheme before this work. Here, we employ this method to shorten the pulse duration even further, demonstrating world-record isolated 67 as pulses.
Optical pulses with attosecond duration are the shortest controllable process up to now and are much faster than the electron response times in any electronic devices. In consequence, it is also a challenge to characterize attosecond pulses experimentally, especially when they feature a broadband spectrum. Similar challenges have previously been met in characterizing femtosecond laser pulses, with many schemes already proposed and well-demonstrated experimentally. Similar schemes can be applied in characterizing attosecond pulses with narrow bandwidth. The limitation of these techniques is presented here, and a method recently developed to overcome those limitations is discussed.
At last, several experimental advances toward the characterization of the isolated 25 as pulses, which is one atomic unit time, are discussed briefly.Ph.D.
Doctorate
Optics and Photonics
Optics and Photonics
Optics and Photonics
38
Miseikis, Lukas. "Attosecond transient absorption experiments in poly(3-hexylthiophene) targets." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/60582.
Abstract:
In this thesis I present the development of a new type of experiment that extends the avenues of common time resolved measurements in the attosecond science field. The work presented here brings the tools of attosecond science to study electron dynamics in the systems that are the central topic in plastic electronics. A new experimental scheme is designed to study exciton formation and evolution in organic semiconductor Poly(3-HexylThiophene) (P3HT) that is used in organic solar cells. A variation of attosecond transient absorption spectroscopy was proposed to study the dynamics. The challenges of this experimental arrangement were to prepare the correct laser targets and both pump and probe pulses. Here I present the development of solid state polymer targets that were used for the transient absorption experiments. These targets have been succesfully prepared as free standing films in the range of 50 nm - 200 nm thickness and their X-ray absorption spectra were measured. Carrier envelope phase stable laser pulses centered at 1750 nm were achieved in a few optical cycle regime via Hollow Core Fiber (HCF) compression scheme developed in house. These pulses were used to drive High Harmonic Generation (HHG) beyond the 160 eV energy range in a differentially pumped Ne gas target. Strong CEP dependent half cycle cutoofs were observed in the HHG spectra confirming isolated attosecond pulses. X-ray absorption spectrum in P3HT targets was measured using this new source. Two routes for the optical pump generation have been explored. 17 fs, 2 mJ pulse was obtained from the 1750 nm driver via the cascaded third harmonic generation process in a non linear crystal and characterised using the SHG-FROG technique. This pulse was implemented as an optical pump in the transient absorption experiment. An interferometric optical setup was constructed that combines both the pump and the probe generation and the delay control between them. The setup was used to obtain the initial transient absorption experiment data.
39
Johnson, Allan Stewart. "Long and short wavelength optical sources for attosecond science." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/61581.
Abstract:
In this thesis I describe work extending attosecond science into new regimes through the development of novel light sources. Thus far attosecond science has been driven primarily through two technologies: titanium-doped sapphire lasers capable of generating few-cycle femtosecond laser pulses in the near infrared (800 nm) wavelength range, and high harmonic generation driven by these pulses, which creates attosecond pulses in the extreme ultraviolet frequency range (10-150 eV). We attempt to move into new regimes for attosecond science through the development of light sources at new wavelengths. Through the use of an optical parametric amplifier and hollow-core fibre pulse compression, we have generated 1.3-cycle pulses at a central wavelength of 1750 nm (7.1 fs duration) with excellent spatio-temporal quality and high energies of 750 uJ per pulse at a repetition rate of 1 kHz. Three novel diagnostics were developed in order to characterize the temporal properties of these pulses: a SEA-F-SPIDER, a third harmonic single-shot FROG, and a third harmonic D-scan. Our short-wavelength infrared laser source has been applied to high harmonic spectroscopy of substituted benzenes. By careful control of macroscopic conditions, we obtain harmonic spectra comparable to theoretical calculations. We find a minimal effect of deuteration upon the few-femtosecond dynamics of benzene. Using the few-cycle 1750 nm pulses, high harmonic generation has been extended to the soft X-ray regime, and we have generated attosecond pulses at all photon energies across the water window (284-540 eV). Energies of tens of picojoules are generated, with estimated pulse durations of several hundred attoseconds. The spatial properties of the harmonic radiation were also examined, and found to be well described by Gaussian optics. Finally, the soft X-ray harmonic radiation was used to obtain X-ray absorption spectra from a variety of samples to demonstrate the utility of our source.
40
Hung, Tsen-Yu. "Towards attosecond measurement of dynamics in multi-electron systems." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/25522.
Abstract:
Recent developments in laser science have made it possible to experimentally study ultrafast electron dynamics in atoms and molecules directly by using ultrashort pulses on the order of tens of attoseconds. It is paramount, both for current understanding and planning of future experiments and applications, that we decipher how short pulses interact with the medium. We model attosecond dynamics of multi-electron systems following three themes: (1) propagation and distortion of pulses in absorbing noble gases, (2) simulation of atoms and molecules under the effects of pump and probe pulses, (3) coherence and polarization effects on transient absorption. First, using the Kramers-Kronig relations and a fast and stable numerical algorithm based on Mobius transformations, we model the distortion of XUV pulses propagating in noble gases. Our simulations show rich features including pulse stretching, partial narrowing, partial apparent super-luminality, and tail development. Second, we deploy the density matrix formalism using Lindblad terms and the three Hilbert spaces method, incorporating multi-channel and Auger ionization compactly and consistently, to model coherence observed in pump-probe attosecond transient absorption studies of Kr II. We explain how coherent noble cation states are produced. Density matrix elements for the excited Kr II 3d_3/2 and 3d_5/2 levels caused by a resonant z-polarized 80 eV 150 as probe pulse are simulated and the resulting population densities and induced dipole moments are analyzed, including nonlinear contributions. In order to model pulse propagation, we develop absorption theory for arbitrary polarization angle and point out how coherence effects distort the Beer-Lambert law and discuss experimental implications. Third, we investigate non-adiabatic effects in attosecond dynamics in molecules driven by a laser field. We use the Algebraic Diagrammatic Construction method and Arnoldi-Lanczos TDSE programs to simulate N2 and oligocenes for 400 nm, 800 nm and 1.6 micron wavelengths with various laser intensities and polarizations. We determine the onset of non-adiabaticity in N2, benzene and naphthalene. Last, but not least, I describe my experimental contribution to the new Imperial College beamline.
41
Lin, Nan. "Application of attosecond pulses to high harmonic spectroscopy of molecules." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-01064138.
Abstract:
High-order Harmonic Generation (HHG) is an extreme nonlinear process that can be intuitively understood as the sequence of 3 steps: i) tunnel ionization of the target atom/molecule, creating an electronic wave packet (EWP) in the continuum, ii) acceleration of the EWP by the strong laser field and iii) recombination to the core with emission of an attosecond burst of XUV coherent light. HHG thus provides a tunable ultrashort tabletop source of XUV/Soft X-ray radiation on attosecond time scale for applications ('direct' scheme). At the same time, it encodes coherently in the XUV radiation the structure and dynamical charge rearrangement of the radiating atoms/molecules ('self-probing' scheme or High Harmonic Spectroscopy). This thesis is dedicated to both application schemes in attophysics based on advanced characterization and control of the attosecond emission. In the so-called 'self-probing' scheme, the last step of HHG, the electron-ion re-collision can be considered as a probe process and the emission may encode fruitful information on the recombining system, including molecular structure and dynamics. In the first part, we performed high harmonic spectroscopy of N₂O and CO₂ molecules that are (laser-)aligned with respect to the polarization of the driving laser. We implemented two methods based on optical and quantum interferometry respectively in order to characterize the amplitude and phase of the attosecond emission as a function of both photon energy and alignment angle. We discovered new effects in the high harmonic generation, which could not be explained by the structure of the highest occupied molecular orbital (HOMO). Instead, we found that during the interaction with the laser field, two electronic states are coherently excited in the molecular ion and form a hole wave packet moving on an attosecond timescale in the molecule after tunnel ionization. We focused on exploring this coherent electronic motion inside the molecule, and compared the measurements in N₂O and CO₂. The striking difference in the harmonic phase behavior led us to the development of a multi-channel model allowing the extraction of the relative weight and phase of the two channels involved in the emission. An unexpected pi/4 phase shift between the two channels is obtained. Moreover, we studied the attosecond profile of the pulses emitted by these two molecules, and we proposed a simple but flexible way for performing attosecond pulse shaping. In the second part, high harmonic spectroscopy was extended to other molecular systems, including some relatively complex molecules, e.g., SF₆ and small hydrocarbons (methane, ethane, ethylene, acetylene). It revealed many interesting results such as phase distortions not previously reported. For the 'direct' scheme, we photoionized rare gas atoms using well characterized attosecond pulses of XUV coherent radiation combined with an infrared (IR) laser "dressing" field with controlled time delay, stabilized down to about ± 60 as. We evidenced marked differences in the measured angular distributions of the photoelectrons, depending on the number of IR photons exchanged. Joined to a theoretical interpretation, these observations bring new insights into the dynamics of this class of multi-color photoionization processes that are a key step towards studying photoionization in the time domain, with attosecond time resolution.
42
Barreau, Lou. "Étude de dynamiques de photoionisation résonante à l'aide d'impulsions attosecondes." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS511/document.
Abstract:
Cette thèse s’intéresse à la photo-ionisation de systèmes atomiques et moléculaires en phase gazeuse à l’aide d’harmoniques d’ordre élevé, un rayonnement cohérent dans le domaine de l’extrême ultraviolet (10-100 eV) sous la forme de trains d’impulsions attosecondes (1 as = 10-18 s). Dans un premier temps, les dynamiques électroniques au cours de l’auto-ionisation de gaz rares sont étudiées par interférométrie électronique. L’auto-ionisation résulte de l’interférence entre un chemin d’ionisation direct et un chemin résonant pour lequel l’atome reste transitoirement piégé dans un état excité.L’amplitude de la transition associée à ces processus est accessible via des expériences de photo-ionisation dans le domaine spectral (sur synchrotron par exemple), mais ce n’est pas le cas de la phase qui est pourtant essentielle à la compréhension de la dynamique électronique.Nous avons développé plusieurs méthodes interférométriques afin de mesurer la phase spectrale associée aux transitions électroniques vers des résonances de Fano dans les gaz rares.A partir des informations dans le domaine spectral, nous avons reconstruit pour la première fois la dynamique d'auto-ionisation ultra-rapide dans le domaine temporel et observé les interférences électroniques donnant lieu au profil de raie asymétrique. Dans un second temps, la photo-ionisation de molécules de NO est étudiée dans le référentiel moléculaire et utilisée comme un polarimètre afin de caractériser complètement l’état de polarisation du rayonnement harmonique, et en particulier de distinguer la partie du rayonnement polarisée circulairement d’une éventuelle partie dépolarisée. Nous présentons les résultats des mesures de polarimétrie moléculaire dans le cas de la génération d’harmoniques par un champ à deux couleurs polarisées circulairement en sens opposé. Ces études, complétées par des simulations numériques, permettent de proposer des conditions optimales de génération de rayonnement harmonique polarisé circulairement et contribuent à ouvrir la voie vers des études de dichroïsme circulaire ultrarapide dans la matièreIn this work, photoionzation of atomic and molecular species in the gas phase is investigated with high-harmonic radiation. In a first part, electronic dynamics in the autoionization process of rare gases in studied with electron interferometry. This method gives access to the spectral phase of the transition to the autoionizing state, and allows there construction of the entire autoionization dynamics. The ultrafast electronic dynamics, as well as the build-up of the celebrated asymmetric Fano profile, are observed experimentally for the first time. In a second part, photoionization of NO molecules in the molecular frame is used as a polarimeter to completeley characterize the polarization state of high-harmonics. In particular, this method can address the challenging disentanglement of the circular and unpolarized components of the light. The experimental results, completed by numerical simulations, allow defining optimal generation conditions of fully circularly-polarized harmonics for advanced studies of ultrafast dichroisms in matte
43
Holzberger, Simon Verfasser], and Ferenc [Akademischer Betreuer] [Krausz. "Enhancement cavities for attosecond physics / Simon Holzberger. Betreuer: Ferenc Krausz." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2015. http://d-nb.info/1081628812/34.
44
Süßmann, Frederik. "Attosecond dynamics of nano-localized fields probed by photoelectron spectroscopy." Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-161443.
Abstract:
This work focuses on the interaction of few-cycle laser pulses with nanosystems. Special emphasis is placed on the spatio-temporal evolution of the induced near-fields. Measurements on carrier-envelope-phase (CEP) controlled photoemission from isolated SiO2 nanospheres are taken by single-shot velocity map imaging (VMI) combined with CEP tagging. The obtained photoelectron spectra show a pronounced dependence on the CEP and extend to unexpectedly high energies. Comparison with numerical simulations identify the additional Coulomb forces of the liberated electron cloud as an effective additional acceleration mechanism for distinct trajectories. For larger spheres, an asymmetry in the field distribution is classically predicted. This asymmetry is also observed in the photoelectron momentum distributions. The mapping between position and momentum space in the VMI approach are investigated by analyzing the correlation of the photoelectron's birth and detection position.
In a second set of experiments, photoemission at intensities exceeding 10^14 W/cm^2 from isolated nanospheres of different composition (SiO2, ZrO2, TiO2, Si, Au) is examined by stereo time-of-flight spectroscopy. It is found that the measured cutoff energies scale non-linearly with laser intensity depending on the material properties of the nanosystem. A trend towards a unified behavior for high intensities is observed indicating a drastic change in optical properties within the duration of the few-cycle laser pulse. The charge carrier generation mechanisms that could lead to such a transient effect are discussed.
For a better understanding of the interaction of few-cycle fields with nanosystems, a direct access to the temporal evolution of (plasmonic) near-fields is highly desirable. The efforts on the realization of nanoplasmonic attosecond streaking spectroscopy are presented. Numerical simulations are used to identify the influence of the inhomogeneous near-field distributions on the streaking process. First experimental results obtained from Au nanotips show clear streaking features of sub-micron localized near-fields. The near-field oscillations are found to be phase offset as compared to reference measurements. The exact origin of the streaking features of the Au tip and possible improvements of the experimental approach are discussed.Im Mittelpunkt dieser Arbeit steht die Wechselwirkung von ultrakurzen Laserpulsen mit Nanosystemen wobei besonderes Augenmerk auf die örtlichen und zeitlichen Eigenschaften der erzeugten Nahfelder gelegt wird. Zur direkten und indirekten Bestimmung der Nahfeldentwicklung und -verteilung wird auf verschiedene Formen der Elektronenspektroskopie zurückgegriffen. Zum einen wird die Photoemission von isolierten SiO2 Nanokugeln mit Hilfe der Velocity-Map-Imaging-Methode bei gleichzeitiger Bestimmung der Träger-Einhüllenden-Phase der ultrakurzen Laserpulse gemessen. Die Impulsspektren zeigen eine starke Abhängigkeit von der Feldentwicklung des Laserfeldes und erstrecken sich zu unerwartet hohen Energien. Mit Hilfe numerischer Simulationen kann gezeigt werden, dass photoionisierte Elektronen eine hochdynamische Ladungsverteilung an der Oberfläche erzeugen, welche für eine zusätzliche Beschleunigung für ausgewählte Elektronentrajektorien verantwortlich ist. Messungen an Nanokugeln mit verschiedener Größe zeigen, dass die durch Propagationseffekte erzeugte asymmetrische Feldverteilung direkt auf die Impulsprojektionen übertragen wird. Die Korrelation zwischen Orts- und Impulsraum der Photoelektronen und eine mögliche Rekonstruktion der Feldverteilung an der Oberfläche werden diskutiert. Mit weiteren Experimenten an einem Stereo-Flugzeitspektrometer wird die Photoemission von Nanoteilchen unterschiedlicher Zusammensetzung (SiO2, ZrO2, TiO2, Si, Au) bei hohen Intensitäten oberhalb von 10^14W/cm^2 untersucht. Diese zeigen eine nichtlineare Abhängigkeit der höchsten Elektronenenergien von der Intensität. Die Gesetzmäßigkeit aller Materialien konvergiert, was ein starkes Indiz für eine drastische Änderung der optischen Eigenschaften noch während des Laserpulses ist. Die verfügbaren theoretischen Modelle zur Erzeugung freier Ladungsträger, die zu einem solchen transienten Effekt führen können, werden diskutiert. Zeitaufgelöste Messungen der Nahfeldoszillationen an Nanoteilchen würden ein tiefgreifenderes Verständnis und Charakterisierung der kollektiven Elektronendynamik ermöglichen. Die Anwendung von Attosekundenpulsen zu diesem Zweck wird diskutiert wobei besonderes Augenmerk auf die inhomogene örtliche Verteilung der Felder an Nanostrukturen gelegt wird. Erste experimentelle Resultate zur Messung der Nahfeldoszillationen an Gold-Nanospitzen werden präsentiert. Die Ergebnisse zeigen einen deutlichen Phasenversatz zu Referenzmessungen. Die örtliche Herkunft des Signals und mögliche Verbesserungen des Experiments werden aufgezeigt.
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Wätzel, Jonas [Verfasser]. "Ultrafast dynamics driven by attosecond and structured photons / Jonas Wätzel." Halle, 2016. http://d-nb.info/1136608591/34.
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Buades, Bárbara. "Attosecond X-ray absorption fine-structure spectroscopy in condensed matter." Doctoral thesis, Universitat Politècnica de Catalunya, 2018. http://hdl.handle.net/10803/663092.
Abstract:
Attoscience aims to study electron dynamics in matter with unprecedented temporal resolution by using the shortest pulses generated on Earth. Currently, such resolution is only provided by sources that deliver attosecond pulses based on the high-harmonic generation (HHG) process. In this thesis we make use of the demonstration of the generation of isolated attosecond pulses in the soft X-ray (SXR) regime covering the entire water window (284 eV to 543 eV) with pulse durations shorter than 300 as. Such a source is used to explore its own development, the spectroscopic capabilities of the pulses as well as the spectroscopic differences from existing X-ray sources, and finally to exploit the potential of the provided extraordinary temporal resolution.
We report on the ability to spectrally tune our source 150 eV across the water window by controlling the pressure during the HHG process and the HHG target position with respect to the focal plane of the driving laser pulse. We associate the changes in pressure and target position to a phase matching change between the driving laser pulse of the HHG process and the generated SXR radiation that is mainly caused by a change in the ionisation fraction. These phase matching changes are also compared to a carrier-to-envelope phase changes of the driving laser field.
The attosecond SXR source is used for X-ray absorption fine structure (XAFS) spectroscopy. Our XAFS studies enable the simultaneous probing of extended XAFS (EXFAS) and near edge XAFS (NEXAFS) in graphite, providing element specificity and orbital sensitivity with identification of the sigma* and pi* orbitals in synchronicity with the material’s four characteristic bonding distances. This illustrates the potential capability of correlating electron dynamics with structural dynamics with attosecond resolution being able to resolve charge migration, electron-phonon coupling and structural transitions. Our XAFS investigations also reveal spectral changes in graphite and TiS2 as a consequence of the shorter attosecond pulse compared to the longer picosecond pulse that are typically used in synchrotron facilities. An extended theory is still required to link Auger electron spectroscopy, total electron yield and XAFS using synchrotron radiation with attoXAFS to decouple the different electron dynamics involved on each of the measurements.
Finally, the attosecond pulses are employed to interrogate charge dynamics with unprecedented temporal resolution inside a compound quasi-2D material, TiS2. By synchronising a 1.85 µm pump pulse with the probing attosecond SXR pulse, we observe that the shape of the X-ray absorption line changes from a Lorentzian distribution to a Fano-type distribution oscillating with twice the pump electric field frequency. The absorption changes appear due to an acquired dipole phase response of the photo-excited core-level electron induced by the consecutive arrival of the infrared pump pulse. This demonstrates that field-driven intra-band dynamics dominate over inter-band dynamics. SXR radiation also provides element specificity of attoXAFS which permits, in combination with theory, the visualisation of the flow of charge amongst the atoms inside the unit cell in real time. The combined spatio-temporal capabilities of attosecond transient XAFS may prove decisive to investigate the correlated motion of carriers in quantum materials such as phase-transitions and superconductors.La Attociencia tiene como objetivo estudiar la dinámica de electrones en la materia con una resolución temporal sin precedentes mediante el uso de los pulsos más cortos generados en la Tierra. Actualmente, dicha resolución solo se puede lograr con fuentes de pulsos de attosegundos basados ¿¿en el proceso de generación de armónicos altos (HHG). En esta tesis hacemos uso de la demostración de la generación de pulsos aislados de attosegundos en el régimen de rayos X blandos (SXR) que cubre toda la ventana de agua (284 eV a 543 eV) con duraciones de pulso más cortos que 300 as. Dicha fuente se utiliza para explorar su propio desarrollo, las capacidades espectroscópicas de los pulsos, así como las diferencias espectroscópicas con las fuentes de rayos X existentes, y finalmente explotar el potencial de la resolución temporal extraordinaria proporcionada. Presentamos primero la capacidad de ajustar espectralmente nuestra fuente 150 eV a lo largo de la ventana de agua mediante el control de la presión del gas atómico involucrado en el proceso de HHG y de la posición del proceso de HHG con respecto al plano focal del láser impulsor de activación del proceso. Asociamos los cambios en la presión y en la posición a un cambio de coincidencia de fase entre el láser impulsor y la radiación SXR generada que es causada principalmente por un cambio en la fracción de ionización. Estos cambios de fase también se comparan con los cambios de fase entre la envolvente del campo y el campo (CEP). La fuente de SXR de attosegundo se utiliza para la espectroscopía de estructura fina de absorción de rayos X (XAFS). Nuestros estudios XAFS permiten el sondeo simultáneo de XAFS extendido (EXFAS) y XAFS cercano al borde (NEXAFS) en grafito, proporcionando especificidad de elemento y sensibilidad orbital con identificación de los orbitales sigma* y pi* en sincronicidad con las cuatro distancias de enlace características del material. Esto ilustra la capacidad potencial de correlacionar la dinámica de electrones con la dinámica estructural con resolución de attosegundos, pudiendo resolver la migración de carga, el acoplamiento electrón-fonón y las transiciones estructurales. Nuestras investigaciones XAFS también revelan cambios espectrales en grafito y TiS2 como consecuencia del pulso de atosegundo más corto en comparación con el pulso de picosegundo más largo que se utilizan normalmente en las instalaciones de sincrotrón. Todavía se requiere una teoría extendida para vincular la espectroscopia electrónica de Auger, el campo total de electrones (TEY) y XAFS utilizando radiación sincrotrón con attoXAFS para desacoplar las diferentes dinámicas electrónicas involucradas en cada una de las mediciones. Finalmente, los pulsos de attosegundo se emplean para analizar la dinámica de carga con una resolución temporal sin precedentes dentro de un material compuesto de cuasi-2D, TiS2. Al sincronizar un pulso de luz de bombeo de 1.85 µm con el pulso SXR de attosegundo, observamos que la línea de absorción de rayos X cambia de una distribución de Lorentzian a una distribución de tipo Fano que oscila con el doble de la frecuencia del campo eléctrico de bombeo. Los cambios de absorción aparecen debido a una respuesta de fase dipolar adquirida del electrón excitado por fotoionicaición por la llegada consecutiva del pulso de bombeo infrarrojo. Con esto se demuestra que las dinámicas dentro de la banda impulsadas por el campo dominan sobre la dinámica entre bandas. La radiación SXR también proporciona especificidad de elemento de attoXAFS que permite, en combinación con la teoría, la visualización del flujo de carga entre los átomos dentro de la celda unitaria en tiempo real. Las capacidades espaciotemporales combinadas del XAFS transitorio de attosegundo pueden ser decisivas para investigar el movimiento correlacionado de portadores en materiales cuánticos, como transiciones de fase y superconductores.
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Schultze, Martin. "Attosecond real time observation of ionization and electron-electron interactions." Diss., kostenfrei, 2008. http://edoc.ub.uni-muenchen.de/9509/.
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Matía, Hernando Paloma. "Attosecond pump-probe methods for measurement of molecular hole dynamics." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/50155.
Abstract:
The generation of few-cycle pulses at near-infrared wavelengths is now a robust technology, as is their application to the efficient production of high-order harmonics in the extreme ultraviolet region with temporal confinement to hundreds of attoseconds. Recent years have seen considerable efforts directed to the study of electron dynamics in complex molecules in real time, with relevance to processes such as photosynthesis and radiation damage of proteins and DNA. This work describes the development of new and unique sources suited for the study of such dynamics, together with novel instrumentation and experimental methodology. This includes a pair of synchronised attosecond pulses at different photon energies in the VUV and XUV regions, which we have generated via high harmonic generation from a few-cycle NIR source and characterised with attosecond streaking. We have also explored the possibilities of sub-cycle control of these attosecond pulses by adding a second harmonic field to the high- harmonic generation process, and simultaneously characterised this second harmonic field with a novel characterisation technique known as ARIES, capable of waveform sampling at arbitrary optical wavelengths. In parallel, we have developed a few-cycle short-wavelength IR source for a UK user facility, to take advantage of the favourable wavelength scaling of the maximum photon energy achievable via high-harmonic generation. Using a commercial optical parametric amplifier and a hollow-core fibre compression system, we have generated sub-2-cycle pulses at 1750 nm, characterised via third-harmonic autocorrelation and a novel implementation of the dispersion scan technique. We have commissioned a beamline for attosecond pump-probe studies in the gas phase, including a purpose-built dual spectrometer with capabilities for simultaneous measurement of mass spectra of ions and velocity-map imaging of electrons. We have performed initial VUV-NIR pump-probe experiments on a small organic molecule, namely isopropanol, and identified a time- dependent signature as an IR-induced coupling. Finally, we have considered perspectives for future studies in attosecond pump-probe experiments with the demonstration of a two-VUV-photon process in helium performed with a moderate energy, high repetition rate attosecond source.
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Fabris, Davide. "Ultrafast light sources and methods for attosecond pump-probe experiments." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/25283.
Abstract:
In this thesis I describe the development of novel light sources to be applied in attosecond pump-probe experiments, together with new methods dedicated to their characterisation and optimisation. Femtosecond pulses are a necessary tool to enter the attosecond domain. For this reason their development is a key element to unlock more capabilities in pump-probe attosecond experiments. The dynamics of generation and compression of few-cycle femtosecond pulses has been studied in a hollow core fibre system. The carrier envelope phase stability performance under increasing input power to the fibre system has been examined systematically, showing the effects of ionisation on the carrier envelope phase stability. Two characterisation techniques have been developed to measure ultrafast femtosecond pulses. A version of the d-scan technique has been demonstrated in the single shot regime for the first time, extending the utility of this diagnostic. An all optical technique (ARIES) for the characterisation of the full waveform of a femtosecond pulse has been developed, exploiting the high harmonics generation process and the sensitivity of the cut-off emission to the instantaneous amplitude of the generating electric field. The main results of the thesis are concerned with the generation of isolated attosecond pulses in new spectral regions. Vacuum ultraviolet few-femtosecond and attosecond pulses have been generated by filtering with metallic foils the high harmonics emission driven by sub-4 fs pulses, and were characterised with the attosecond streaking technique. When using indium as spectral filter a pulse duration of 1.7±0.1 fs was measured at a photon energy of 15 eV. When using tin as spectral filter a pulse duration of 585±31 as was measured at a photon energy of 20 eV. The experimental techniques developed in this thesis allow these pulses to be generated simultaneously with a XUV pulse with a measured duration of 270±25 as. This work will open new opportunities for pump-probe experiments, for example studies of ultrafast charge migration in large molecules.
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Liao, Chen-Ting, and Chen-Ting Liao. "Exploring Ultrafast Quantum Dynamics of Electrons by Attosecond Transient Absorption." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/624293.
Abstract:
Quantum mechanical motion of electrons in atoms and molecules is at the heart of many photophysical and photochemical processes. As the natural timescale of electron dynamics is in the range of femtoseconds or shorter, ultrashort pulses are required to study such phenomena. The ultrashort pulse light-matter interaction at high intensity regime can however dramatically alter the atomic and molecular structures. Our current understanding of such transient electronic modification is far from complete, especially when complicated light-induced couplings are involved. In this dissertation, we investigated how a femtosecond strong-field pulse can control or modify the evolution of atomic or molecular polarization, representing electric dipole excitation in various systems. Extreme ultraviolet (XUV) attosecond pulse trains are used to coherently prepare superposition of excited states in various atomic and molecular systems. A subsequent phase-locked infrared (IR) femtosecond pulse is applied to perturb the dipoles, and transient changes in the transmitted XUV spectra are measured. This scheme is termed as XUV attosecond transient absorption spectroscopy. In the first study, we applied this technique to study the modification of Rydberg states in dilute helium gas. We observed several transient changes to the atomic structure, including the ac Stark shift, laser-induced quantum phase, laser-induced continuum structure, and quantum path interference. When the experiments were extended to the study of a dense helium gas sample, new spectral features in the absorption spectra emerged which cannot be explained by linear optical response models. We found that these absorption features arise from the interplay between the XUV resonant pulse propagation and the IR-imposed phase shift. A unified physical model was also developed to account for various scenarios. Extending our work to argon atoms, we studied how an external infrared field can be used to impulsively control different photo-excitation pathways and the transient absorption lineshape of an otherwise isolated autoionizing state. It is found that by controlling the field polarization of the IR pulse, we can modify the transient absorption line shape from Fano-like to Lorentzian-like profiles. Unlike atoms, in our study of autoionizing states of the oxygen molecule, we observed both positive and negative optical density changes for states with different electronic symmetries. The predictions of two distinct and simplified dipole perturbation models were compared against both the experimental results and a full theoretical calculation in order to understand the origin of the sign of absorption change. We relate this symmetry-dependent sign change to the Fano parameters of static photoabsorption. The same approach was applied to study molecular nitrogen, in which we observed the decay dynamics of IR perturbed doubly-excited Rydberg states with many vibrational progressions. In addition, we also conducted experiments to investigate Rydberg state dynamics of other molecular systems such as carbon dioxide. In summary, we experimentally explored the ephemeral light-induced phenomena associated with excited states of atoms and molecules. These studies provide real-time information on ultrafast electronic processes and provide strategies for direct time-domain control of the light-matter interaction.