Download or read book From Few cycle Femtosecond Pulse to Single Attosecond Pulse controlling and Tracking Electron Dynamics with Attosecond Precision written by He Wang and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Proceedings of the 8th International Conference on Attosecond Science and Technology written by Argenti 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 open access volume brings together selected papers from the 8th International Conference on Attosecond Science and Technology. The contributions within represent the latest advances in attosecond science, covering recent progress in ultrafast electron dynamics in atoms, molecules, clusters, surfaces, solids, nanostructures and plasmas, as well as the generation of sub-femtosecond XUV and X-ray pulses, either through table-top laser setups or with X-ray free-electron lasers. In addition to highlighting key advances and outlining the state of the field, the conference and its proceedings serve to introduce junior researchers to the community, promote collaborations, and represent the global and topical diversity of the field.
Download or read book Improved Control of Single Cycle Pulse Generation by Molecular Modulation written by Andrea Mihaela Burzo and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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 (EIT like) 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).
Download or read book Study on Generation of Attosecond Pulse with Polarization Gating written by Shambhu Ghimire and published by . This book was released on 2007 with total page 135 pages. Available in PDF, EPUB and Kindle. Book excerpt: Finally, in order to temporarily characterize the attosecond pulses we designed and built an "Attosecond Streak Camera". Most of such cameras to date are limited to measuring a 1 dimensional energy spectrum and have only a few degrees of acceptance angle. Our camera is capable of measuring 2d momentum of the photoelectrons with large acceptance angle, for example ∼65° at the photoelectron of energy ∼15 eV. Recently, we observed the sidebands in addition to the main peaks in their laser assisted XUV photoelectron spectrum. The single attosecond pulses, after being characterized with this high speed camera, can be used to explore the dynamics of electrons at the attosecond scale.
Download or read book Isolated Attosecond Pulses Using a Detuned Second harmonic Field written by and published by . This book was released on 2007 with total page 3 pages. Available in PDF, EPUB and Kindle. Book excerpt: Calculations are presented for the generation of an isolated attosecond pulse in a multicycle two-color strong-field regime. We show that the recollision of the electron wave packet can be confined to half an optical cycle using pulses of up to 40 fs in duration. The scheme is proven to be efficient using two intense beams, one producing a strong field at [omega] and the other a strong field detuned from 2[omega]. The slight detuning [delta][omega] of the second harmonic is used to break the symmetry of the electric field over many optical cycles and provides a coherent control for the formation of an isolated attosecond pulse.
Download or read book Connecting Lab Based Attosecond Science with FEL Research written by and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In the last few years laboratory-scale femtosecond laser-based research using XUV light has developed dramatically following the successful development of attosecond laser pulses by means of high-harmonic generation. Using attosecond laser pulses, studies of electron dynamics on the natural timescale that electronic processes occur in atoms, molecules and solids can be contemplated, providing unprecedented insight into the fundamental role that electrons play in photo-induced processes. In my talk I will briefly review the present status of the attosecond science research field in terms of present and foreseen capabilities, and discuss a few recent applications, including a first example of the use of attosecond laser pulses in molecular science. In addition, I will discuss very recent results of experiments where photoionization of dynamically aligned molecules is investigated using a high-harmonics XUV source. Photoionization of aligned molecules becomes all the more interesting if the experiment is performed using x-ray photons. Following the absorption of x-rays, ejected photoelectrons can be used as a probe of the (time-evolving) molecular structure, making use of intra-molecular electron diffraction. This amounts, as some have stated, to "illuminating the molecule from within". I will present the present status of our experiments on this topic making use of the FLASH free electron laser in Hamburg. Future progress in this research field not only depends on the availability of better and more powerful light sources, but also requires sophisticated detector strategies. In my talk I will explain how we are trying to meet some of the experimental challenges by using the Medipix family of detectors, which we have already used for time- and space-resolved imaging of electrons and ions.
Download or read book Generation and Characterization of Sub 70 Isolated Attosecond Pulses written by Qi Zhang and published by . This book was released on 2014 with total page 115 pages. Available in PDF, EPUB and Kindle. Book excerpt: Dynamics occurring on microscopic scales, such as electronic motion inside atoms and molecules, are governed by quantum mechanics. However, the Schrödinger 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.
Download or read book Modeling Generation and Characterization of Attosecond Pulses written by Siddharth Bhardwaj and published by . This book was released on 2014 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Towards High flux Isolated Attosecond Pulses with a 200 TW CPA written by Eric Cunningham and published by . This book was released on 2015 with total page 194 pages. Available in PDF, EPUB and Kindle. Book excerpt: To obtain the microjoule-level attosecond pulse energy required for performing all-attosecond experiments, the attosecond flux generated by the IFAST 10 TW system was still deficient by an order of magnitude. To this end, the laser system was upgraded to provide joule-level output energies while maintaining pulse compression to 15 fs, with a targeted peak power of 200 TW. This was accomplished by adding an additional Ti:sapphire amplifier to the existing 10 TW system and implementing a new pulse compression system to accommodate the higher pulse energy. Because this system operated at a 10 Hz repetition rate, stabilization of the carrier-envelope phase (CEP)--important for controlling attosecond pulse production--could not be achieved using traditional methods. Therefore, a new scheme was developed, demonstrating the first-ever control of CEP in a chirped-pulse amplifier (CPA) at low repetition rates. Finally, a new variation of optical gating was proposed as a way to improve the efficiency of the attosecond pulse generation process. This method was also predicted to allow for the generation of isolated attosecond pulses with longer driving laser pulses, as well as the extension of the highenergy photon cut-off of the XUV continuum.
Download or read book Generation and Application of Attosecond Pulses written by Zsolt Diveki and published by . This book was released on 2011 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Generation of Few cycle and Attosecond Pulses and Their Use in Probing Ultrafast Dynamics in Gases and Surfaces written by Christopher Arrell and published by . This book was released on 2011 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book High energy Isolated Attosecond Pulses by Sub cycle Ionization Dynamics written by Federico Ferrari and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Attosecond Pulse Generation and Characterization written by Razvan Cristian Chirla and published by . This book was released on 2011 with total page 208 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: One of the research goals in the DiMauro group is the application of attosecond light pulses for understanding electronic processes and for molecular imaging. The objective of this dissertation work was the construction of an attosecond beamline at The Ohio State University, and the implementation of the so-called Rabbitt technique.
Download or read book Attosecond Strong Field Control written by Mirko Holler and published by Sudwestdeutscher Verlag Fur Hochschulschriften AG. This book was released on 2010 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt: High-order harmonics are a unique tool to investigate dynamics in atomic and molecular systems as they allow the generation of pulses with attosecond duration. In this thesis, high-order harmonics are investigated experimentally in temporal and spectral domain. In spectral domain, an interference structure between the two shortest electron quantum paths of the generation process is observed. These interferences are investigated with laser intensities below, around and above the intensity of barrier suppression. To enable attosecond time-resolved measurements, a versatile beamline is developed and implemented. Typical attosecond experiments rely on a cross-correlation measurement of the combined XUV / IR fields with attosecond resolution. Attosecond pulse trains (APT) are temporally characterized by means of a RABBITT (reconstruction of attosecond beating by interference of two photon transitions) measurement. These APTs are then used in an all-optical XUV/IR pump-probe measurement in a dense helium gas target. The absorption is influenced by a strong IR field. This experiment can be regarded as the first all-optical XUV/IR pump-probe measurement with attosecond resolution.
Download or read book Generation of Short and Intense Attosecond Pulses written by Sabih ud Din Khan and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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 [mu]J 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.
Download or read book Characterization and Application of Isolated Attosecond Pulses written by Michael Chini and published by . This book was released on 2012 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Few cycle Pulses Amplification for Attosecond Science Applications written by Michaël Hemmer and published by . This book was released on 2011 with total page 230 pages. Available in PDF, EPUB and Kindle. Book excerpt: The emergence of mode-locked oscillators providing pulses with durations as short as a few electric-field cycles in the near infra-red has paved the way toward electric-field sensitive physics experiments. In addition, the control of the relative phase between the carrier and the pulse envelope, developed in the early 2000's and rewarded by a Nobel price in 2005, now provides unprecedented control over the pulse behaviour. The amplification of such pulses to the millijoule level has been an on-going task in a few world-class laboratories and has triggered the dawn of attoscience, the science of events happening on an attosecond timescale. This work describes the theoretical aspects, modeling and experimental implementation of HERACLES, the Laser Plasma Laboratory optical parametric chirped pulse amplifier (OPCPA) designed to deliver amplified carrier-envelope phase stabilized 8-fs pulses with energy beyond 1 mJ at repetition rates up to 10 kHz at 800 nm central wavelength. The design of the hybrid fiber/solid-state amplifier line delivering 85-ps pulses with energy up to 10 mJ at repetition rates in the multi-kHz regime tailored for pumping the optical parametric amplifier stages is presented. The novel stretcher/compressor design of HERACLES, suitable for handling optical pulses with spectra exceeding 300 nm of bandwidth with unprecedented flexibility, is fully modeled and also presented in the frame of this thesis. Finally, a 3D model of the multi-stage non-collinear optical parametric amplifier is also reported. The current and foreseen overall performances of HERACLES are presented. This facility is designed to enable attosecond physics experiments, high-harmonic generation and physics of plasma studies.
