Dissertations / Theses on the topic 'Higher order harmonics'
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Chowdhury, Rehana Momtaz Engineering & Information Technology Australian Defence Force Academy UNSW. "Use of Higher Order Harmonics from a Limiter to Improve the Single-Tone Detection Performance of an Envelope Detector." Awarded by:University of New South Wales - Australian Defence Force Academy. Engineering & Information Technology, 2009. http://handle.unsw.edu.au/1959.4/43512.
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The limiter is a commonly used device in communication receiving systems to remove the amplitude variations of the received signal, but it is usually observed that limiter degrades the envelope detection performance of a single tone. In this thesis, it is demonstrated that the limiter-generated third harmonic can be used to improve the envelope detection performance of a single tone over that of the linearly processed fundamental. Differences in the probability distributions of the limiter-generated harmonics cause differences in their detection probabilities, which lead to differences in the performance of subsequent envelope detection. Comparison of the envelope detection performance of the limiter-generated third harmonic and the input to the limiter shows a maximum detection probability gain of 1.12 and also error probability gain of 2.4 in linear scale, whereas the fundamental harmonic does not show any practically significant gain. The envelope detection performance of the vector sum of the limiter-generated fundamental and third harmonics is also evaluated. This combination provides better performance than do the individual harmonics, especially for a large clipping parameter of the limiter. The combined harmonics shows a maximum detetction probability gain of 1.15 and error probability gain of 14, over that of the envelope detection performance of a tone without limiter. It is also observed that the envelope detection performance of a tone with limiter-generated higher harmonics shows non-monotonic behaviour as functions of either noise or the limiter-clipping parameter, which is a signature of stochastic resonance. The theoretical results from earlier research on the envelope detection of a single tone embedded in additive white Gaussian noise, both with and without a limiter, are presented and shown to match our simulation results. In previous work when a limiter was used in the envelope detection of a single tone, only the envelope of the fundamental harmonic was considered under very specific conditions. By contrast we also take notice of the limiter-generated higher harmonics and obtain improved envelope detection performance in the detection of a single tone.
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Schapper, Florian. "Attosecond structure of high-order harmonics." Konstanz Hartung-Gorre, 2010. http://d-nb.info/1000540448/04.
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Hammond, Thomas John. "Intracavity generation of high order harmonics." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/39747.
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The goal of this work is the generation of extreme ultraviolet (EUV) radiation from a laser based source. To this end, we use high harmonic generation (HHG) to convert the near infrared output of a mode-locked Ti:Sapphire laser oscillator to the EUV. The requirement for HHG is a high peak intensity (>10¹³ W/cm²), which can be met by external amplification of the laser output. The method of amplification chosen for this work is a femtosecond enhancement cavity (fsEC), which stores and amplifies the output of a femtosecond mode-locked Ti:Sapphire laser by greater than a factor of 900 while maintaining the original repetition rate of 66 MHz. The design, benefits, and limitations of using a fsEC are discussed. The EUV light is created by the interaction of the amplified light with xenon gas delivered to the fsEC focus. The strong intracavity field leads to xenon plasma generation with detrimental effects on the HHG process, where it is shown that HHG is sensitive to the xenon gas and plasma dynamics. Methods of minimizing the plasma density and maximizing the EUV amplitude are discussed. The EUV is coupled out of the cavity, and up to the thirteenth harmonic (61 nm) of the laser is observed. The relative amplitudes of the different quantum trajectories generating the harmonics are calculated theoretically, and compared to experiment. The generated power of the eleventh harmonic (72 nm) is estimated to be 30μW, with a measured outcoupled power of 1.1μW. The relative intensity noise is also measured, with a cumulative root-mean-square (RMS) noise of <1.2% over 100 Hz - 100 kHz bandwidth. In comparison to other laser based HHG systems, while the EUV flux is similar, the cumulative RMS noise is an order of magnitude lower.
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Wagner, Nicholas L. "High-order harmonic generation from molecules." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3303823.
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Zhu, Xuemei. "A higher-order panel method for third-harmonic diffraction problems." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/43339.
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Kaassamani, Shatha. "Polarization Spectroscopy of High Order Harmonic Generation in Semiconductors Orbital angular momentum from semiconductor high-order harmonics All semiconductor enhanced highharmonic generation from a single nanostructured cone." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP091.
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Depuis sa première observation, la génération d'harmonique d'ordre élevé (HHG) dans les cristaux s'est avérée d'être une source efficace, contrôlable et compacte de rayonnement XUV cohérent. Dans cette thèse, nous étudions la génération d'harmonique d'ordre élevé (HHG) dans le graphène, et dans différents semi-conducteurs principalement oxyde de zinc, silicium, arséniure de gallium et oxyde de magnésium. Nous observons que les propriétés du laser, notamment l'intensité, polarisation et ellipticité ainsi que les propriétés du cristal impactent de manière corrélée au processus de génération d'harmonique. De plus, nous surlignons le rôle important des effets de propagation linéaire et non linéaire, surtout l'effet Kerr, qui peut modifier l'efficacité de génération d'harmonique. Bien que ceux-ci induisent des limitations, dans certaines conditions ils présentent un avantage. Finalement, nous démontrons la possibilité d'augmenter localement l'intensité du laser par confinement dans un cône nanostructuré et ainsi d’accroître le flux harmonique généré. Enfin, nous démontrons une application en imagerie par diffraction cohérente de la source harmonique nanostructuréeSince its first observation, a decade ago, high harmonic generation (HHG) in crystals has proved to be an efficient, controllable and compact source of coherent XUV radiation. In this thesis, we investigate HHG in 2D materials, particularly graphene, and in different semiconductor crystals mainly zinc oxide, silicon, gallium arsenide and magnesium oxide. We find that the laser properties, such as its intensity, polarization and ellipticity, and the crystal properties are interrelated. Moreover, we shed the light on the role of the linear and nonlinear propagation effects mainly the Kerr effect, upon laser interaction with the crystal, which can significantly influence the high harmonic generation efficiency. Although this presents major limitations, we show that in some cases it turns out to be an advantage. Finally, we demonstrate the manipulation of the harmonic radiation at the source of the emission by patterning nanostructures to confine and enhance nanojoule laser pulses, and generate harmonic beams carrying orbital angular momentum. Lastly, we successfully image a micrometer-sized sample by the coherent diffractive imaging (CDI) technique based on solid-state harmonics
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Kong, Fanqi. "High-Order Harmonic Generation with Structured Beams." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39609.
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The generation of high-order harmonics opened an era of attosecond science wherein coherent light bursts are used to probe dynamic processes in matter with a time resolution short enough to resolve the motions of electrons. It enabled the development of extreme ultraviolet (XUV) and X-ray table-top sources with both temporal and spatial coherence, which provides the ability to shape the temporal and spatial structure of the XUV pulses.
Scientists developed techniques to control and measure the temporal structure high harmonic emissions. These techniques exploited control of the driving laser pulse in the time domain and facilitated development of more advanced high-harmonic based XUV sources that have greatly impacted ultrafast measurements.
In this thesis, I apply techniques to control and measure the spatial structure of high harmonic emissions, and discuss the underlying physics and potential applications of the interaction between spatially structured laser beams and materials. This study exploits the spatial degree of freedom in strong field interaction, which has not been given as much attention as the temporal degree of freedom.
I use liquid crystal devices to shape the wave front of a fundamental laser beam to a vortex structure, then imprint this structured wave front onto XUV beams through high harmonic generation. This method provides an alternative to special XUV optics, which can manipulate the wave front of XUV radiation by all optical means. This result also reveals the conservation of orbital angular momentum in this extreme nonlinear wave mixing process. In addition to shaping the wave front, shaping the polarization of the driving beam also allows generation of circularly polarized the XUV radiation using a high harmonic source.
This thesis also highlights the interplay between shaping the wave front and polarization in the high harmonic generation process. The topology of the structured beam can be maintained through this extreme nonlinear interaction due to the spin selection rules and spin-orbit conservation.
Moreover, this thesis demonstrates an approach to integrate a vector beam into a broadband ultrafast light source and overcome the bandwidth limitation of mode converters. We use this approach to generate a few-cycle structured beam. In the future, this beam will be used to generate a strong ultrafast magnetic impulse in gas and solid targets by driving currents in a loop, which is a valuable tool for the future of magnetic metrology.
The novel properties of structured laser beams discussed in this thesis expanded the capabilities of high harmonic based XUV sources and have opened a new field to explore this additional degree of freedom in strong field interactions.
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Yijian, Meng. "Extreme Ultraviolet Hyperspectral Coherent Diffractive Imaging." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/31928.
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We demonstrate hyperspectral imaging using two time-delayed, coherent extreme ultraviolet (XUV) sources. The approach combines broadband XUV high-harmonic generation, holographic imaging, and Fourier transform spectroscopy. The two harmonics sources are spatially separated at generation,and overlap in the far field resulting in a double slit diffraction pattern. We record the two-dimensional intensity modulation as a function of relative time delay; the Fourier transform determines the spatially dependent spectrum. To reduce the delay jitter and improve the spectral resolution, we demonstrate a novel experimental setup that records the relative delay of the two pulses through optical interference. Moreover, we have demonstrated that this broadband approach can be extended to Fourier transform holographic imaging, which avoids extensive phase retrieval computations. Applications include imaging of biological materials near the carbon K-edge.
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Brimhall, Nicole. "Extreme Ultraviolet Polarimetry with Laser-Generated High-Order Harmonics." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd1926.pdf.
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Goodell, Brian Carpenter, and Brian Carpenter Goodell. "Probing Intracavity Plasma Dynamics with Higher-Order Transverse Modes." Thesis, The University of Arizona, 2017. http://hdl.handle.net/10150/625686.
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Extreme ultraviolet (XUV) frequency combs exhibit promise for enabling high-precision spectroscopic measurements of myriad chemical species for the first time. Coherent XUV radiation can be generated through high harmonic generation (HHG) in femtosecond enhancement cavities. HHG efficiency is limited by nonlinear phase shifts induced by residual intracavity plasma. The goal of this work is to gain insight regarding plasma dynamics in order to allay the detrimental effects of plasma interactions. Our approach is to conduct simulations of cavity pump-probe experiments by probing with higher-order transverse modes. We propose methods for estimating spatial plasma profiles, gas jet velocities, and the plasma recombination coefficient based on measurements of plasma-induced phase shifts. Beam distortion due to plasma interaction is analyzed and used as another reference for plasma dynamics.
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Tisch, John William George. "Studies of high harmonic generation using high power lasers." Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309530.
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Alharbi, Abdullah F. "High-order Harmonic Spectroscopy of Cyclic Organic Molecules." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35179.
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Understanding the electronic structure and dynamics of cyclic organic molecules is becoming increasingly the subject of investigations from different perspectives due to their unique chemical and physical properties. Since they are largely involved in the biochemistry of living organisms, studies on this class of compounds are also valuable to understand biologically relevant complex systems. Compared to other techniques, high-order harmonic generation (HHG) has been increasingly considered as a powerful spectroscopic tool with Angstrom spatial and attosecond temporal resolutions. This thesis demonstrates that high-order harmonic spectroscopy is capable of providing structural and dynamical information on the electronic systems of representative cyclic organic molecules comprising randomly oriented five-membered or six-membered rings.
The first part of this thesis shows that the HHG from these molecules is sensitive to their aromatic character, which results from the de-localized pi electrons, and can potentially be a useful qualitative measure of aromaticity. We show that the advantage of utilizing HHG in this direction stems from the result that only pi molecular orbitals, associated with aromatcity, are responsible for the HHG emission in aromatic systems.
The capability of HHG to distinguish cyclic isomers is demonstrated in the case of xylene molecules. Supported by numerical calculations, differences in the isomers are attributed to both tunnel ionization and photorecombination, the first and last steps of HHG. These results enable further HHG-based time-resolved studies of the dynamics associated with isomeric effects that these molecules exhibit.
The present work also challenges the well-established prediction that strong field ionization from a molecular orbital is suppressed along nodal planes, where the electron density is zero. In fact, our study shows that considerable tunnel ionization in some cyclic molecules can occur near or along nodal planes. This unusual ionization is reported to have its signature on the quantitative and qualitative dependence of harmonic yield on laser ellipticity.
The high symmetry displayed by the cyclic molecule, 1,4 cyclohexadiene, is shown to leave its imprints on the HHG in the form of structural interferences even if the target is randomly oriented. Two-color HHG from this molecule also indicates that hole dynamics could be involved in the generation process.
A general study on high harmonic spectroscopy of the Cooper minimum in molecules is also reported. The presence of this minimum could affect the interpretation of harmonics spectra in any molecule containing S or Cl atoms. The molecular environment is shown to influence the position of this spectral modulation.
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Hutchison, Christopher. "High-order harmonic generation in laser ablation plumes." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/40289.
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High harmonic generation (HHG) is a powerful and well established technique to study ultra fast processes in atoms and molecules. Originally HHG was restricted to the study of atomic or small molecular gases. In the last few years the use of laser ablation to create plumes that are suitable media for HHG has gained interest due to is ability to allow almost any solid material to be potentially studied using HHG. Most of this thesis focuses on our advancements in this eld of ablation plume HHG spectroscopy with a small section devoted to our continuation of work focused on controlling electron trajectories in HHG through the use of an orthogonally polarised second harmonic eld. We show how through the use of a rotating target system we have been able to stabilise the ablation process to work at 1 kHz repetition rate. The ablation plumes of some transition metals have previously be shown to exhibit enhancement of particular harmonic orders linked to resonances in the parent ion. We performed investigations into tin and manganese plumes and were able to nd good agreement between the experimental data and a theoretical model. This showed that autoionising states in the ions of these materials were the most likely source of the enhancements. We present our attempts to extend the ablation plume HHG technique to work with soft materials. It was found that graphite plumes were able to produce a very strong harmonic response that is comparable with generation from an argon gas jet. It was discovered that nano particles were present in the plumes and these were mostly likely to cause of the stronger e ciency. Finally we present the rst use of laser ablation plume HHG to study molecules of biological interest. We performed HHG studies on uracil and thymine, a signal was obtained from former but not the latter. Were able to determine that during ablation there was a higher degree of molecular fragmentation from thymine molecules compared to uracil.
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Sutherland, Julia Robin Miller. "Phase-Matching Optimization of Laser High-Order Harmonics Generated in a Gas Cell." Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd880.pdf.
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Pfullmann, Nils [Verfasser]. "Nano-antenna-assisted high-order harmonic generation / Nils Pfullmann." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2012. http://d-nb.info/1031117709/34.
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Anderson, Patrick. "High-order harmonic generation with self-compressed femtosecond pulses." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/375102/.
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Here, a state-of-the-art model is developed that can predict both the evolution of an intense laser pulse propagating through a gas-filled fibre, and the extreme ultraviolet field that it generates. This model is first used to discover a new mechanism for compressing energetic laser pulses to few cycle durations within short gas-filled fibres at pressures where high-order harmonic generation is routinely performed. Next, the fibre design is optimised for enhanced phase-matching using the model. Once fabricated and integrated into the source characterisation apparatus, the conversion efficiency at 30-40 nm is found to be almost an order of magnitude higher than comparable sources. Preliminary simulations also predict that isolated attosecond pulses may emerge from the fibre if parameters are carefully tuned. Additionally, a 13.5 nm source is developed in an extended gas cell geometry. Filters suitable for this wavelength are tested and a single harmonic is then selected and brought to a focus. This apparatus is now being used by the wider scientific community to image test objects and biological samples.
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Zhang, Pei. "Beam position diagnostics with higher order modes in third harmonic superconducting accelerating cavities." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/beam-position-diagnostics-with-higher-order-modes-in-third-harmonic-superconducting-accelerating-cavities(587aa24b-8adc-4bc6-8f5c-475aa0028d06).html.
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Higher order modes (HOM) are electromagnetic resonant fields. They can be excited by an electron beam entering an accelerating cavity, and constitute a component of the wakefield. This wakefield has the potential to dilute the beam quality and, in the worst case, result in a beam-break-up instability. It is therefore important to ensure that these fields are well suppressed by extracting energy through special couplers. In addition, the effect of the transverse wakefield can be reduced by aligning the beam on the cavity axis. This is due to their strength depending on the transverse offset of the excitation beam. For suitably small offsets the dominant components of the transverse wakefield are dipole modes, with a linear dependence on the transverse offset of the excitation bunch. This fact enables the transverse beam position inside the cavity to be determined by measuring the dipole modes extracted from the couplers, similar to a cavity beam position monitor (BPM), but requires no additional vacuum instrumentation.At the FLASH facility in DESY, 1.3 GHz (known as TESLA) and 3.9 GHz (third harmonic) cavities are installed. Wakefields in 3.9 GHz cavities are significantly larger than in the 1.3 GHz cavities. It is therefore important to mitigate the adverse effects of HOMs to the beam by aligning the beam on the electric axis of the cavities. This alignment requires an accurate beam position diagnostics inside the 3.9 GHz cavities. It is this aspect that is focused on in this thesis. Although the principle of beam diagnostics with HOM has been demonstrated on 1.3 GHz cavities, the realization in 3.9 GHz cavities is considerably more challenging. This is due to the dense HOM spectrum and the relatively strong coupling of most HOMs amongst the four cavities in the third harmonic cryo-module. A comprehensive series of simulations and HOM spectra measurements have been performed in order to study the modal band structure of the 3.9 GHz cavities. The dependencies of various dipole modes on the offset of the excitation beam were subsequently studied using a spectrum analyzer. Various data analysis methods were used: modal identification, direct linear regression, singular value decomposition and k-means clustering. These studies lead to three modal options promising for beam position diagnostics, upon which a set of test electronics has been built. The experiments with these electronics suggest a resolution of 50 micron accuracy in predicting local beam position in the cavity and a global resolution of 20 micron over the complete module. This constitutes the first demonstration of HOM-based beam diagnostics in a third harmonic 3.9 GHz superconducting cavity module. These studies have finalized the design of the online HOM-BPM for 3.9 GHz cavities at FLASH.
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Lohbreier, Jan. "Characterization and Optimization of High-order Harmonics after Adaptive Pulse Shaping." kostenfrei, 2008. http://www.opus-bayern.de/uni-wuerzburg/volltexte/2009/3047/.
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Spagnol, Marco. "Maintenance of electrical machines: Instantaneous Angular Speed analysis." Doctoral thesis, Università degli studi di Trieste, 2015. http://hdl.handle.net/10077/11102.
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2013/2014This research is focused on the condition monitoring of electrical machines and its long term purpose is to monitor electrical and mechanical faults at the same time, in non-stationary conditions (variable load and speed), with a single piece of hardware. The Instantaneous Angular Speed (IAS) measurement of an electrical machine is proposed and analysed in order to detect the fault development inside it. Chapter 1 introduces some basic principles about the maintenance of an electrical machine. Machine unscheduled downtimes are frequently caused by bearing faults, and rotor/stator faults. Monitoring systems are needed when the machine is very important for the plant (cost, safety). In this chapter, the electrical machine’s behaviour is also examined. Induction electrical machines have been chosen for this research. A review of the excitation frequencies is reported in the chapter. In the last section, characteristic fault frequencies (from mechanical and electrical sources) are collected. Chapter 2 presents the IAS measurement and its signal processing. The IAS is the measurement of the shaft rotating speed in order to visualize what’s happening during a single or in multiple turns. There are many measurement methods which are based either analogical to digital conversion or which use counters. Analogical to digital methods use a standard data acquisition board. Counter methods have to use specific hardware that is more expensive, but with less data to store. In this research, the counter method is used, combined with the Elapsed Time (ET) counting technique. Chapter 3 describes the encoder system. Its output signal is acquired with an oscilloscope and with the counter board. The signal’s differences are highlighted. In this chapter, the measurement’s source of errors are listed: the encoder’s geometrical error, the counter’s quantization error, the clock stability and the general electrical noise. Chapter 4 collects all the experimental tests done during the PhD research. Three experimental test rigs are shown and two measurements at Nidec ASI S.p.A. are reported. Note that the experimental test rigs were designed and built at the Università degli Studi di Trieste during the three years of the PhD. Experimental Test Rig 1 (ETR1) is used to understand the electrical motor’s behaviour with varying speed, the difference between the IAS and the speed acquired with the Torsional Laser Vibrometer, the difference between the IAS and the acceleration signal measured with an accelerometer located on the motor’s stator, the effect of the unbalance in the IAS measurement. Experimental Test Rig 2 (ETR2) allows to examine the load effect on the IAS measurement, the magneto-motive force harmonics, the slip and the rotor effects. Experimental Test Rig 3 (ETR3) is designed in order to detect the Inner Race Bearing Fault (Ball Pass Frequency Inner - BPFI) with varying load. The acceleration, the voltage and the current are compared with the Instantaneous Angular Speed. The motor is also tested with an unbalanced power supply. The two measurements at Nidec ASI S.p.A show how the IAS measurement could be implemented in an industrial machine larger than the one tested in the laboratory. This research presents the pros and cons of the IAS measurement, highlighting the capability of detecting BPFI bearing fault, feeling the load variations owing to the brake system (a synchronous generator), measuring the Fundamental Train Frequency of an healthy bearing, detecting unbalance in the rotor and other special features. The author would like to thank the Fondo Sociale Europeo, the Regione Friuli Venezia Giulia and Nidec ASI S.p.A (an electrical motor company) for the sponsorship and the collaboration during the three PhD years covered by the SHARM project ”Manutenzione Preventiva Integrata”.
Questo studio è focalizzato al monitoraggio dello stato di salute delle macchine elettriche con l'obbiettivo finale di monitorare danni meccanici ed elettrici, in condizioni non stazionarie (carico e velocità variabili), con un singolo sistema hardware. Viene quindi proposta ed analizzata la misura della Velocità Angolare Istantanea (Instantaneous Angular Speed - IAS) di una macchina elettrica allo scopo di prevedere l'insorgere di guasti al suo interno. Il Capitolo 1 introduce i principi base relativi alla manutenzione di macchine elettriche. Di frequente, le fermate non programmate sono conseguenti a danni su cuscinetti e su rotore/statore. I sistemi di monitoraggio sono indispensabili quando la macchina è molto importante nel contesto dell'impianto, considerazione esaminata sia dal punto di vista del costo che della sicurezza. In questo capitolo, viene analizzato anche il funzionamento della macchina elettrica. Dopo un'attenta valutazione, per lo sviluppo di questa ricerca sono state selezionate le macchine ad induzione asincrone. Nel capitolo è riportata anche un'analisi bibliografica sulle frequenze caratteristiche delle forzanti elettromagnetiche presenti. Nell'ultima sezione vengono elencate le frequenze tipiche dei danni rilevabili in misure di tipo vibrazionale ed elettrico. Il Capitolo 2 presenta la misura IAS. Questa rappresenta la misurazione della velocità di rotazione dell'albero e viene analizzata con accuratezza, individuando la relazione tra velocità di rotazione e le caratteristiche dell'encoder; inoltre vengono descritti i vari processamenti del segnale. Tale sistema permette di visualizzare ciò che sta accadendo alla macchina durante il suo funzionamento, in una o più rotazioni. Esistono metodi di misura basati o sulla conversione analogico-digitale o che prevedono l’impiego di contatori. I primi si servono di una scheda di acquisizione dati standard, mentre i secondi richiedono l'utilizzo di un hardware specifico, che alle volte può risultare più costoso, ma permette di acquisire i dati occupando una quantità inferiore di memoria. In questa tesi si è scelto di utilizzare un contatore per eseguire la misura IAS, sfruttando il conteggio Elapsed Time (ET). Il Capitolo 3 descrive l'encoder. Il segnale in uscita dal dispositivo viene acquisito con una scheda contatore e con un oscilloscopio in modo da confrontare ed analizzare le differenze presenti. In questo capitolo vengono elencate le tipologie di errore presenti nel sistema encoder: l'errore geometrico, l'errore di quantizzazione, l'errore dovuto alla stabilità del clock interno e l'errore dovuto a fonti esterni di rumore elettrico. Il Capitolo 4 raccoglie tutti i test sperimentali condotti durante il dottorato. Sono stati progettati e costruiti tre setup allo scopo di evidenziare particolari aspetti e problematiche; sono riportate anche due misure eseguite presso la sala prove dell'azienda Nidec ASI S.p.A. Il setup Experimental Test Rig 1 (ETR1) è stato utilizzato per conseguire le seguenti finalità: capire il funzionamento del motore elettrico con velocità variabile, analizzare la differenza della velocità acquisita con un torsiometro laser ed una scheda contatore, confrontare una misura vibrazionale (accelerometro posizionato sullo statore del motore) e la misura IAS, analizzare l'effetto dello sbilanciamento sulla misura IAS. Il setup Experimental Test Rig 2 (ETR2) permette di esaminare l'effetto del carico sulla misura IAS, le armoniche della forza elettromotrice, l'effetto dello slip e del rotore. Il setup Experimental Test Rig 3 (ETR3) è progettato in modo da evidenziare un difetto sulla guida interna di un cuscinetto, considerando anche un carico variabile. L'accelerazione, il voltaggio e la corrente sono confrontate con la Velocità Angolare Istantanea. Il motore viene testato anche applicando una tensione di alimentazione sbilanciata. Le due misure rilevate in Nidec ASI S.p.A dimostrano che la misura IAS può essere implementata in macchine industriali di grandi dimensioni e non solo nei setup di laboratorio. Questa ricerca espone gli aspetti positivi e negativi della misura IAS, evidenziando le capacità di individuare un danno sulla guida interna di un cuscinetto, captare le variazioni di carico prodotte dal freno (un generatore sincrono), misurare la Fundamental Train Frequency di un cuscinetto in buona salute, individuare uno sbilanciamento ed altre funzionalità. L'autore vuole ringraziare il Fondo Sociale Europeo, la Regione Friuli Venezia Giulia e l'azienda Nidec ASI S.p.A (produttore di macchine elettriche di medio-grandi dimensioni) per la sponsorizzazione e la collaborazione durante i tre anni di dottorato previsti dal progetto SHARM ”Manutenzione Preventiva Integrata”.
XXVII Ciclo
1983
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Painter, John. "Direct observation of laser filamentation in high-order harmonic generation /." Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1316.pdf.
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Kurz, Heiko Gustav [Verfasser]. "High-order harmonic spectroscopy with water droplets / Heiko Gustav Kurz." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2014. http://d-nb.info/105103776X/34.
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Knapke, Robert. "High-Order Unsteady Heat Transfer with the Harmonic Balance Method." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1427962937.
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Painter, John Charles. "Direct Observation of Laser Filamentation in High-Order Harmonic Generation." BYU ScholarsArchive, 2006. https://scholarsarchive.byu.edu/etd/433.
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We investigate the spatial evolution of an intense laser pulse as it generates high-order harmonics in a long gas cell, filled with 80 torr of helium. A thin foil separates the gas-filled region of the cell from a subsequent evacuated region. The exit plane of the gas cell can be scanned along the laser axis so that the evolution of the laser throughout the focus can be observed (full scanning range of 9 cm). We constructed an apparatus that images the laser radial energy profile as it exits the cell. The high harmonics, odd orders ranging from 45 to 91, are observed at the same time that the laser spot is characterized. Re-absorption of the harmonics within the gas cell restricts the region of harmonic emission to the final centimeter (or less) of the cell. We present the first direct evidence (to our knowledge) of laser filamentation under conditions ideal for high-order harmonic generation. The 30 fs, 4 mJ, laser pulses were observed to undergo double focusing within the gas cell, with about 4 cm separating the two foci. The region with best harmonic emission occurs midway between the two foci. The radial profile of the laser focus, 150-200 microns in diameter, evolves from a Gaussian-like profile to a more square-top profile as it propagates over several centimeters. The filamentation phenomenon as well as the brightness of the harmonics improves when an aperture is partially closed on the laser beam before reaching the focusing mirror. A spectral sampling of the imaged laser focus revealed a 4 nm blue-shift associated with the generation of plasma in the gas cell. The blue-shifting occurs primarily in the center of the laser beam and less at the wider radii. The initial laser pulse had a spectrum centered at 800 nm with a 35 nm bandwidth. The energy associated with each of the observed 26 harmonic beams was found to be approximately 1 nJ, yielding a conversion efficiency of approximately 2e−7.
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Cheng, Rendy P. "A high-order, linear time-invariant model for application to higher harmonic control and flight control system interaction." College Park, Md. : University of Maryland, 2003. http://hdl.handle.net/1903/46.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2003.Thesis research directed by: Aerospace Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Brimhall, Nicole. "Extreme Ultraviolet Polarimetry with Laser-Generated High-Order Harmonics: Characterization of Uranium." BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/1824.
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We developed an extreme ultraviolet (EUV) polarimeter, which employs laser-generated high-order harmonics as the light source. This relatively high-flux, directional EUV source has available wavelengths between 10 nm and 47 nm with easily rotatable linear polarization. The polarimeter has allowed us to characterize the optical constants of materials that may be useful for EUV optics. The instrument has a versatile positioning system and a spectral resolution of about 180, and we have demonstrated that reflectance as low as 0.1% can be measured repeatably at EUV wavelengths. We investigate the high harmonic source used for polarimetry measurements by documenting the spatial evolution of the generating laser in a semi-infinite helium-filled gas cell under conditions suitable for harmonic generation. The laser is observed to focus, diverge, and refocus, accompanied by a flattop beam profile and extended harmonic phase matching. We numerically simulate the propagation to investigate these experimental results. We find that harmonic energy comes from the forward portion of the laser pulse, whereas the latter portion gives rise to the incidental double laser focusing. Good phase matching for the harmonics arises in large measure from a balance between the linear phase delay of the neutral atoms and the Gouy shift, which is elongated and nearly linearized when an aperture is partially closed on the beam. We compare reflectance data taken with the polarimeter instrument with expected results from well-characterized samples and find that they agree. To improve repeatability and reduce the effects of systematic measurement errors we have measured the ratio of p- to s-polarized reflectance and shown that optical constants can be extracted from this data as efficiently as from absolute reflectance measurements. These ratio measurements allow more accurate recovery of optical constants than our absolute reflectance measurements for our well-characterized samples. We use the polarimeter instrument and the ratio reflectance technique to determine the optical constants of copper, uranium, and their natural oxides from 10-47 nm. For copper, this measurement resolves previously conflicting data sets, where disagreement on optical-constant values arises from failure to keep samples from oxidizing before measurement. Uranium has been proposed as a high-reflectance material in the EUV for several years, however difficulties with oxidation have prevented its careful characterization previous to this work. We find that measured optical constants for uranium do not agree well with previously accepted theoretical calculations.
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Voronov, Sergei Leonidovich. "Controlling laser high-order harmonic generation using weak counter-propagating light /." Diss., CLICK HERE for online access, 2003. http://contentdm.lib.byu.edu/ETD/image/etd146.pdf.
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Voronov, Sergei Leonidovich. "Controlling Laser High-Order Harmonic Generation Using Weak Counter-Propagating Light." BYU ScholarsArchive, 2002. https://scholarsarchive.byu.edu/etd/49.
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Laser high-order harmonic generation in the presence of relatively weak interfering light is investigated. The interfering pulses intersect the primary harmonic-generating laser pulse at the laser focus. The interfering light creates a standing intensity and phase modulation on the field, which disrupts microscopic phase matching and shuts down local high harmonic production. Suppression of the 23rd harmonic (by two orders of magnitude) is observed when a counter-propagating interfering pulse of light is introduced. A sequence of counter-propagating pulses can be used to shut down harmonic production in out-of-phase zones of the generating volume to achieve quasi phase matching. Harmonic emission is enhanced in this case. A new high-power laser system with higher pulse energy has been constructed to further investigate quasi phase matching of high-order harmonics generated in difficult-to-ionize atomic gases (e.g., neon as opposed to argon). The new system can also be used to study harmonic generation in ions. A new counter-propagating beam produces a train of 5 pulses with regulated timing. In preliminary tests, the new system has produced high harmonics up to the 65th order in neon. This should increase with additional adjustments to the laser system. The high-order harmonics have also demonstrated to be useful for polarized reflectometry measurements of optical surfaces in the extreme ultraviolet (EUV) wavelength range.
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Lytle, Amy Louise. "Phase matching and coherence of high-order harmonic generation in hollow waveguides." Connect to online resource, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3315842.
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Cao, Wei. "Pump-probe study of atoms and small molecules with laser driven high order harmonics." Diss., Kansas State University, 2014. http://hdl.handle.net/2097/18161.
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Doctor of PhilosophyDepartment of Physics
Itzhak Ben-Itzhak and Charles Lewis Cocke
A commercially available modern laser can emit over 10^15 photons within a time window of a few tens of femtoseconds (10^-15 second), which can be focused into a spot size of about 10 um, resulting in a peak intensity above 10^14 W/cm^2. This paves the way for table-top strong field physics studies such as above threshold ionization (ATI), non-sequential double ionization (NSDI), high order harmonic generation (HHG), etc.. Among these strong laser-matter interactions, high order harmonic generation, which combines many photons of the fundamental laser field into a single photon, offers a unique way to generate light sources in the vacuum ultraviolet (VUV) or extreme ultraviolet (EUV) region. High order harmonic photons are emitted within a short time window from a few tens of femtoseconds down to a few hundreds of attoseconds (10^-18 second). This highly coherent nature of HHG allows it to be synchronized with an infrared (IR) laser pulse, and the pump-probe technique can be adopted to study ultrafast dynamic processes in a quantum system. The major work of this thesis is to develop a table-top VUV(EUV) light source based on HHG, and use it to study dynamic processes in atoms and small molecules with the VUV(EUV)-pump IR-probe method. A Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) apparatus is used for momentum imaging of the interaction products. Two types of high harmonic pump pulses are generated and applied for pump-probe studies. The first one consists of several harmonics forming a short attosecond pulse train (APT) in the EUV regime (around 40 eV). We demonstrate that, (1) the auto-ionization process triggered by the EUV in cation carbon-monoxide and oxygen molecules can be modified by scanning the EUV-IR delay, (2) the phase information of quantum trajectories in bifurcated high harmonics can be extracted by performing an EUV-IR cross-correlation experiment, thus disclosing the macroscopic quantum control in HHG. The second type of high harmonic source implemented in this work is a single harmonic in the VUV regime (around 15 eV) filtered out from a monochromator. Experiments on D_2 molecules have been conducted using the 9th or the 11th harmonic as the pump pulse. Novel dissociative ionization pathways via highly excited states of D_2 have been revealed, thus suggesting potential applications for time-resolved studies and control of photochemistry processes.
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Alves, Carla. "Studying ultrafast magnetization dynamics through Faraday effect and using linearly polarized high order harmonics." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS328.
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Dans cette thèse, nous démontrons qu’un rayonnement harmonique XUV polarisé linéairement peut être utilisé en spectroscopie d’absorption pour accéder à l’état de magnétisation de tout type d’échantillon, contrairement à toutes les techniques développées jusque-là. En effet, pour la première fois, des expériences résolues en temps ont été réalisées par l'effet Faraday magnéto-optique, que nous exploitons autour du seuil d'absorption magnétiquement dichroïque M2,3 du Cobalt à 60 eV. La technique pompe-sonde a été utilisée pour obtenir la réponse dynamique des échantillons magnétiques lors de l'excitation laser. Les changements dans l’aimantation de l'échantillon sont associés aux changements dans la polarisation du faisceau harmonique de sonde, i.e. à la fois à la rotation de l’axe de polarisation et à la variation de l'ellipticité. Les principaux résultats de cette thèse démontrent que la mesure de l’effet Faraday offre un moyen ultrasensible de caractériser l’aimantation de films très minces (seulement quelques nm de matériaux magnétique). De plus, l’effet Faraday ayant lieu sur une large plage spectrale il est possible de suivre la dynamique simultanée de différents matériaux et donc d’étudier des matériaux très complexesIn this thesis, we demonstrate that a linearly polarized XUV harmonic radiation can be employed in absorption spectroscopy to access the magnetization state of any type of sample, unlike all the techniques developed so far. Indeed, for the first time, time-resolved experiments were realized through the magneto-optical Faraday effect, which we exploit around the magnetically dichroic Co M2,3 absorption edge at 60 eV. The pump-probe technique was used to obtain the dynamic response of the magnetic samples upon laser excitation. The changes in the magnetization of the sample are associated to the changes in the polarization of the probe harmonic beam, i.e. the rotation of the polarization axis and the variation of the ellipticity. The main results of this thesis demonstrate that the measurement of the Faraday effect offers an ultra-sensitive way to characterize the magnetization of very thin films (only a few nm of magnetic materials). Moreover, since the Faraday effect takes place over a wide spectral range, it is possible to follow the simultaneous dynamics of different materials and thus to study very complex materials
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Gaudiosi, David M. "High power ultrafast laser design and high-order harmonic generation in capillary discharge plasmas." Diss., Connect to online resource, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3239457.
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Yoshii, Kazumichi. "High-Order Harmonic Generation from Coherently Rotating Molecules with High-Intensity Ultrashort Laser Pulses." Kyoto University, 2010. http://hdl.handle.net/2433/120416.
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Schoun, Stephen Bradley. "Attosecond High-Harmonic Spectroscopy of Atoms and Molecules Using Mid-Infrared Sources." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1436853089.
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Aghabarati, Ali. "Multilevel and algebraic multigrid methods for the higher order finite element analysis of time harmonic Maxwell's equations." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=121485.
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The Finite Element Method (FEM) applied to wave scattering and quasi-static vector field problems in the frequency domain leads to sparse, complex-symmetric, linear systems of equations. For large problems with complicated geometries, most of the computer time and memory used by FEM goes to solving the matrix equation. Krylov subspace methods are widely used iterative methods for solving large sparse systems. They depend heavily on preconditioning to accelerate convergence. However, application of conventional preconditioners to the "curl-curl" operator which arises in vector electromagnetics does not result in a satisfactory performance and specialized preconditioning techniques are required. This thesis presents effective Multilevel and Algebraic Multigrid (AMG) preconditioning techniques for p-adaptive FEM analysis. In p-adaption, finite elements of different polynomial orders are present in the mesh and the system matrix can be structured into blocks corresponding to the orders of the basis functions. The new preconditioners are based on a p-type multilevel Schwarz (pMUS) approximate inversion of the block structured system. A V-cycle multilevel correction starts by applying Gauss-Seidel to the highest block level, then the next level down, and so on. On the other side of the V, Gauss-Seidel iterations are applied in the reverse order. At the bottom of the cycle is the lowest order system, which is usually solved exactly with a direct solver. The proposed alternative is to use Auxiliary Space Preconditioning (ASP) at the lowest level and continue the V-cycle downwards, first into a set of auxiliary, node-based spaces, then through a series of progressively smaller matrices generated by an Algebraic Multigrid (AMG). The algebraic coarsening approach is especially useful for problems with fine geometric details, requiring a very large mesh in which the bulk of the elements remain at low order. In addition, for wave problems, a "shifted Laplace" technique is applied, in which part of the ASP/AMG algorithm uses a perturbed, complex frequency. A significant convergence acceleration is achieved. The performance of Krylov algorithms is further enhanced during p-adaption by incorporation of a deflation technique. This projects out from the preconditioned system the eigenvectors corresponding to the smallest eigenvalues. The construction of the deflation subspace is based on efficient estimation of the eigenvectors from information obtained when solving the first problem in a p-adaptive sequence. Extensive numerical experiments have been performed and results are presented for both wave and quasi-static problems. The test cases considered are complicated to solve and the numerical results show the robustness and efficiency of the new preconditioners. Deflated Krylov methods preconditioned with the current Multilevel/ASP/AMG approach are always considerably faster than the reference methods and speedups of up to 10 are achieved for some test problems.La méthode des éléments finis (FEM) appliquée à la dispersion des ondes et aux problèmes de champ de vecteurs quasi-statique dans le domaine fréquentiel mène à des systèmes d'équations linéaires rares, symétriques-complexes. Pour de grands problèmes ayant des géométries complexes, la plupart du temps et de la mémoire d'ordinateur utilisé par FEM va à la résolution de l'équation de la matrice. Les méthodes itératives de Krylov sont celles largement utilisées dans la résolution de grands systèmes creux. Elles dépendent fortement des préconditionnement qui accélèrent la convergence. Toutefois, l'application de préconditionnements conventionnels à l'opérateur "rot-rot" qui surgit en électromagnétisme vectoriel n'aboutit pas à des résultats satisfaisants et des techniques de préconditionnement spécialisés sont exigées.Cette thèse présente des techniques de préconditionnement efficaces multiniveau et multigrilles algébrique (AMG) pour l'analyse p-adaptative FEM. Dans la p-adaptation, des éléments finis de différents ordres polynomiaux sont présents dans le maillage et la matrice du système peut être structurée en blocs correspondant aux ordres des fonctions de base. Les nouveaux préconditionneurs sont basés sur un type d'inversion approximative à multiniveau p Schwarz (pMUS) du système structuré de bloc. Une correction à niveaux multiples en cycle V débute par l'application de Gauss-Seidel au niveau du bloc le plus élevé, suivi par le niveau inférieur, et ainsi de suite. De l'autre côté du V, des itérations de Gauss-Seidel sont appliquées en ordre inverse. Au bas du cycle se trouve le système d'ordre le plus bas, qui est habituellement résolu exactement avec un solveur direct. L'alternative proposée est d'utiliser l'espace auxiliaire de préconditionnement (ASP) au niveau le plus bas et de poursuivre le cycle en V vers le bas, d'abord en un ensemble d'auxiliaires, basé sur les espacements de nœuds, à travers une série de plus en plus petites de matrices générées par un multigrille algébrique (AMG). L'approche de grossissement algébrique est particulièrement utile aux problèmes ayant de fins détails géométriques, nécessitant une très grande maille dans laquelle la majeure partie des éléments restent à un niveau plus bas.En outre, pour des problèmes d'onde, la technique "décalé Laplace" est appliquée, dans laquelle une partie de l'algorithme ASP/AMG utilise une fréquence complexe perturbée. Une accélération de la convergence significative est atteinte. La performance des algorithmes de Krylov est davantage renforcée au cours du p-adaptation par l'incorporation d'une technique de déflation. Cette saillie fait dépasser hors du système préconditionné, les vecteurs propres correspondants aux plus petites valeurs propres. La construction du sous-espace de déflation est basée sur une estimation efficace des vecteurs propres à partir d'informations obtenues lors de la résolution du premier problème dans une séquence p-adaptatif. Des expériences numériques approfondies ont été effectuées et les résultats sont présentés à la fois aux problèmes d'onde et quasi-statiques. Les cas de test sont considérés comme compliqués à résoudre et les résultats numériques montrent la robustesse et l'efficacité des nouveaux préconditionnements. Les méthodes de Krylov de déflation préconditionnés par l'approche multiniveaux/ASP/AMG actuelle sont toujours considérablement plus rapides que les méthodes de référence et des accélérations allant jusqu'à 10 sont atteintes pour certains problèmes de test.
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Steingrube, Daniel Sebastian [Verfasser]. "High-order harmonic generation with ultra-short pulses from filamentation / Daniel Sebastian Steingrube." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2011. http://d-nb.info/1014322367/34.
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Ghimire, Shambhu. "Study on generation of attosecond pulse with polarization gating." Diss., Manhattan, Kan. : Kansas State University, 2007. http://hdl.handle.net/2097/283.
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Jin, Cheng. "Theory of nonlinear propagation of high harmonics generated in a gaseous medium." Diss., Kansas State University, 2012. http://hdl.handle.net/2097/13690.
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Doctor of PhilosophyDepartment of Physics
Chii-Dong Lin
In this thesis, we establish the theoretical tools to investigate high-order harmonic generation (HHG) by intense infrared lasers in a gaseous medium. The macroscopic propagation of both the fundamental and the harmonic fields is taken into account by solving Maxwell’s wave equations, while the single-atom (or single-molecule) response is obtained by quantitative rescattering theory. The initial spatial mode of the fundamental laser is assumed either a Gaussian or a truncated Bessel beam. On the examples of Ar, N[subscript]2 and CO[subscript]2, we demonstrate that the available experimental HHG spectra with isotropic and aligned target media can be accurately reproduced theoretically even though the HHG spectra are sensitive to the experimental conditions. We show that the macroscopic HHG can be expressed as a product of a macroscopic wave packet and a photorecombination cross section, where the former depends on laser and experimental conditions while the latter is the property of the target only. The factorization makes it possible to retrieve the single-atom or single-molecule structure information from experimental HHG spectra. As for the multiple molecular orbital contribution in HHG, it causes the disappearance of the minimum in the HHG spectrum of aligned N[subscript]2 with the increase of laser intensity, and the position of minimum in HHG spectrum of aligned CO[subscript]2 depending on many factors is also attributed to it, which could explain why the minima observed in different laboratories may differ. For an important application of HHG as ultrashort light source, we show that measured continuous harmonic spectrum of Xe due to the reshaping of the fundamental laser field can be used to produce an isolated attosecond pulse by spectral and spatial filtering in the far field. For on-going application of using HHG to ionize aligned molecules, we present the photoelectron angular distribution from aligned N[subscript]2 and CO[subscript]2 in the laboratory frame, which can be compared directly with future experiments.
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Augstein, B. B. "Orbit based treatments of quantum interference in atomic and molecular high-order harmonic generation." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1349184/.
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Orbit-based theoretical approaches to modelling strong eld phenomena allow physical intuition to be extracted from complex multi-dimensional quantum processes. Highorder harmonic generation (HHG) has been interpreted relatively successfully for almost two decades as a three step process in which an ionized electron is accelerated by the eld and recombines with its parent ion, resulting in high-order multiples of the laser frequency. This process is often modelled within the strong-eld approximation (SFA), where the eect of the Coulomb potential on the electron is neglected while the electron is accelerated by the eld, and the single-active electron (SAE) approximation. The SFA provides an appealing interpretation of HHG in terms of interfering electron trajectories. Although successful in reproducing experimental observables in atomic systems, in recent years the importance of multi-electron eects, molecular orbital symmetry and the Coulomb potential in atoms and diatomic molecules have been seen experimentally and theoretically. These eects, neglected by the original SFA formulation, mean that either modications to the original SFA, or new trajectory based theories, are essential for a more complete physical understanding of the HHG phenomenon. This thesis investigates these eects in HHG from homonuclear and heteronuclear diatomic molecules in strong elds. We model and assess the importance of multiple molecular orbital contributions, molecular orbital geometry and two-centre interference on the HHG spectrum. These problems are approached within a semi-analytical, SFA, framework and with a static core. It is found that these eects can be seen in the HHG spectrum. By predicting novel features in the spectrum arising from such eects we obtain not only a better understanding and interpretation of current experimental results, but also new insight and applicability to molecular imaging. In addition to these modications, a new theoretical approach, the coupled coherent state (CCS) method is used to model Hydrogen in an intense eld, although it can be extended to multi-electron systems and diatomic molecules. In the CCS method, the Coulomb potential is fully included at all stages in the HHG process, and most notably, during the electron propagation, where it is neglected by the SFA. The CCS method has favourable scaling with dimensionality, compared to other numerical approaches, as well as being fully quantum. It is trajectory based, facilitating comparison with the three step model and the strong eld approximation. Therefore we benet from the physical intuition of semi-classical approaches but within a fully quantum framework and without the approximations of semi-analytical methods.
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Tortora, Alessandra. "Study and applications of the coherence properties of supercontinuum and high-order harmonic sources." Paris 6, 2006. http://www.theses.fr/2006PA066587.
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Paul, Ariel J. "Coherent EUV light from high-order harmonic generation: Enhancement and applications to lensless diffractive imaging." Connect to online resource, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3273819.
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Viotti, Anne-Lise. "Efficient generation and characterization of soft x-ray by laser-driven high-order harmonic generation." Thesis, KTH, Tillämpad fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-185796.
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Rawat, Vineet. "Finite Element Domain Decomposition with Second Order Transmission Conditions for Time-Harmonic Electromagnetic Problems." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243360543.
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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.
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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.
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Chambers, Michael. "Investigations of the brightness of high order harmonics generated by intense laser interactions with solid and gaseous targets." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298394.
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Staedter, David. "Femtosecond time-resolved spectroscopy in polyatomic systems investigated by velocity-map imaging and high-order harmonic generation." Toulouse 3, 2013. http://thesesups.ups-tlse.fr/2116/.
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Dans cette thèse, la dynamique de photodissociation de l'azoture de chlore (ClN3) est étudiée dans le domaine temporel par imagerie de vecteur vitesse des photofragments, spécialement du chlore et de N3. Cette imagerie résolue à l'échelle femtoseconde permet d'extraire les temps de dissociation, l'établissement temporel de la balance d'énergie de la réaction ainsi que la conservation des moments. Cette étude a permis de différencier deux domaines d'énergie: l'un menant à la formation d'un fragment N3 linéaire (étude autour de 4. 5 eV d'excitation électronique) et le plus intéressant aboutissant à la formation d'un fragment N3 cyclique (autour de 6 eV). Dans une seconde étude, la dynamique de relaxation électronique du tétrathiafulvalène (C6H4S4-TTF) est étudiée autour de 4 eV par spectroscopie de masse résolue en temps ainsi que par spectroscopie de photoélectron. Les seuils d'ionisation dissociative sont extraits d'une détection en coïncidence entre les photoélectrons de seuil et les fragments ionisés réalisée sur rayonnement synchrotron. Les deux dernières expériences sont basées sur la génération d'harmoniques d'ordre élevé dans l'XUV d'une impulsion femtoseconde à 800 nm ou à 400 nm. Dans la première expérience, les harmoniques sont couplées à un imageur de vecteur vitesse en tant que rayonnement secondaire VUV. Par imagerie de photoélectron résolue en temps, nous avons révélé ainsi les dynamiques de relaxation des états de Rydberg initiée par une impulsion femtoseconde XUV à 15. 5 eV dans l'argon et à 9. 3 eV dans l'acétylène. Dans la seconde expérience, couramment nommée spectroscopie attoseconde, les harmoniques constituent le signal pompe sonde. Deux types de spectroscopie attoseconde ont été réalisés pour étudier la dynamique vibrationnelle de SF6: une expérience en réseau transitoire créé par deux impulsions pompe Raman avec une impulsion sonde intense générant les harmoniques à partir du réseau d'excitation et une expérience d'interférence de deux rayonnement XUV en champ lointain créés par deux impulsions sonde intensesRevealing the underlying ultrafast dynamics in molecular reaction spectroscopy demands state-of-the-art imaging techniques to follow a molecular process step by step. Femtosecond time-resolved velocity-map imaging is used to study the photodissociation dynamics of chlorine azide (ClN3). Here especially the co-fragments chlorine and N3 are studied on the femtosecond timescale in two excitation energy regions around 4. 67 eV and 6. 12 eV, leading to the formation of a linear N3 fragment and a cyclic N3 fragment, respectively. This work is the first femtosecond spectroscopy study revealing the formation of cyclic N3. Tetrathiafulvalene (TTF, C6H4S4) electronic relaxation is studied, while scanning the electronic excitation around 4 eV, by time resolved mass and photoelectron spectroscopy. As only few is known about the ion continuum about TTF the imaging photoelectron photoion coincidence (iPEPICO) technique is used in order to disentangle the complex ionic dissociation. The second part of the thesis is based on the generation and application of XUV light pulses by high-order harmonic generation with an intense femtosecond laser pulse in a molecular target. Two types of phase sensitive attosecond spectroscopy experiments were conducted to study the vibrational dynamics of SF6: one using strong field transient grating spectroscopy, where high-order harmonic generation takes place in a grating of excitation, and the second experiment using high-order harmonic interferometry using two intense XUV probe pulses. The temporal dependencies in phase and amplitude reveal the vibrational dynamics in SF6 and demonstrate that high-order harmonic generation is sensitive to the internal excitations. Last but not least, the use of high-order harmonics as a XUV photon source for the velocity-map imaging spectrometer is investigated. Using time-resolved photoelectron imaging, the relaxation dynamics initiated with 15. 5 eV in argon and 9. 3 eV in acetylene are revealed
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Lévêque, Camille. "Pump-probe spectroscopy of vibronic dynamics using high-order harmonic generation : general theory and applications to SO2." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066513/document.
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La molécule SO2 est connue depuis longtemps dans la pour son spectre d'absorption compliqué résultant de forts couplages entre les états électroniques impliqués. Cette longue histoire a récemment été complétée par de nouvelles études spectroscopiques résolues en temps; la spectroscopie de photoémission (TRPES) et la génération d'harmoniques d'ordre élevé. De nouvelles questions ont ainsi émergées, concernant le rôle des différents états électroniques excités, les différents couplages et leur temps caractéristiques. Pour répondre à ces questions, nous avons considéré, dans un premier temps, l'état électronique fondamental et les deux premiers états singulets excités. Ceux-ci interagissent par l'intermédiaire de couplage non-adiabatic, conduisant à la complexité du spectre d'absorption. Nos résultats se sont avérés particulièrement précis, en particulier pour la description des bandes de Cléments, donnant lieu à leur première description et interprétation théorique. Le couplage spin-orbite et les états triplets ont été introduits dans la description du système et l'analyse de la dynamique a permis de comprendre les différents mécanismes de conversion intersystème. Trois résultats majeurs sont obtenus, (i) le rôle prédominant d'un état 3B2, (ii) la présence d'interférences quantiques lors du processus et (iii) une nouvelle interprétation de la bande dite " interdite ", émanant des état triplets. Les spectroscopies TRPES et HHG ont été utilisées pour sonder la dynamique moléculaire dans ces états. Grâce à des simulations ab-initio nous montrons que la méthode TRPES permet l'étude la dynamique pour tous les états alors que la HHG n'est sensible qu'à la conversion intersystèmeThe SO2 molecule is long known in the literature for its complex UV absorption spectrum, which is caused by a variety of strong couplings between the electronic states involved. This long and rich history was augmented recently by new time-dependent spectroscopic methods, namely, Time-Resolved Photoelectron Spectroscopy (TRPES) and High-order Harmonic Generation (HHG). Additional open questions emerged immediately, e.g., what was the role of the different known electronic states, which were the relevant couplings and also the timescales of the different relevant processes.To resolve these issues theoretically, we start by considering the electronic ground state and the two lowest singlet excited states. The latter interact through non-adiabatic couplings leading to a complex photoabsorption spectrum. Our results were accurate, especially concerning the Clements bands, and provide a comprehensive description of the photoabsorption spectrum. When including the spin-orbit coupling, relevant for the weak long-wavelength absorption system, the three-states model turns into a 12 coupled-states system. Analysis of the different couplings gives insight into the different mechanisms of the intersystem crossing. Three main points are shown: (i) the preponderant role of a 3B2 state, (ii) the possibility of quantum interferences during the process and (iii) a new interpretation of the forbidden band.The TRPES and the HHG spectroscopies have been used to probe the time-dependent dynamics in all these states. With the aid of first-principles simulations we show that the TRPES method is sensitive to the dynamics in the manifold, while HHG is sensitive only to the intersystem crossing
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Simoncig, Alberto. "The role of the electron recoiling mechanism in coherent light high-order harmonics generation: from the source to the applications." Doctoral thesis, Università degli studi di Trieste, 2010. http://hdl.handle.net/10077/3581.
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2008/2009I processi di generazione di armoniche di ordine superiore (High-order Harmonic Generation o HHG) in gas inerti rappresentano, attualmente, la tecnica piu` promettente per la creazione di impulsi di luce coerente nell'estremo ultra-violetto (EUV) in una configurazione table-top. I processi HHG si basano sull'interazione non-lineare, tra impulsi laser ultra-corti, tipicamente dell'ordine della decina di femtosecondi, e atomi di gas inerti. Le caratteristiche che distinguono i processi HHG sono la loro durata temporale, che puo` essere nel dominio degli attosecondo e il fatto che l'interazione e` non perturbativa. Invece, la natura quantistica dei processi HHG implica la presenza di meccanismi di diffusione che influenzano la funzione d'onda dell'elettrone atomico coinvolto nell'interazione con il campo laser. Il ruolo della diffusione viene usualmente trascurato nella letteratura corrente, sebbene quest'ultima sia strettamente legata al controllo dell'efficienza del processo HHG e dello stato di polarizzazione dei fotoni generati. Il lavoro di tesi e` focalizzato sullo studio sperimentale e teorico/fenomenologico del ruolo dei meccanismi di diffusione, e sul loro controllo, al fine di incrementare l'efficienza e la qualita` ottica, i.e. coerenza, struttura temporale, etc., dei fotoni HHG prodotti. Gli studi e gli esperimenti condotti forniscono, in base alla nostra attuale conoscenza, la prima dimostrazione quantitativa a supporto del modello di Leweinstein. Accanto alla caratterizzazione spettrale, viene presentato uno studio accurato circa le condizioni minime necessarie a generare impulsi HHG, sempre legate al ruolo della diffusione della funzione d'onda elettronica. I risultati hanno permesso di ottenere una piu` profonda comprensione della complessa dinamica non-lineare, che sta alla base dei processi HHG. Accanto allo studio della diffusione si e` cercato di ottenere il controllo sullo stato di polarizzazione degli impulsi HHG, i quali mantengono la polarizzazione della radiazione laser utilizzata. La stessa diffusione impedisce di creare efficientemente armoniche di ordine superiore con polarizzazione ellittica (o circolare). Per risovere questo problema e` stata abbiamo sviluppato una collaborazione con il gruppo CXRO del Lawrence Berkeley National Laboratory, (Berkeley, USA), grazie al quale sono state realizzate una serie di ottiche multistrati innovative basate sul principio dell'angolo di Brewster, e disegnate appositamente per polarizzare circolarmente impulsi di luce EUV. Queste ultime sono state preliminarmente testate con successo sulla beam-line 6.3.2 del sincrotrone di Berkeley. La parte finale della tesi presenta la prima sorgente di impulsi HHG, polarizzati circolarmente utilizzando i citati multistrati. Per verificare l'efficienza e` di questi multistrati e` stato condotto un esperimento di dicroismo magnetico circolare con radiazioni EUV (EUV-MCD), unico nel sul genere, in quanto utilizza gli impulsi HHG polarizzati circolarmente per sondare il comportamento dicroico in corrispondenza delle soglie di assorbimento M di metalli ferromagnetici come Fe e Ni o delle loro leghe. Il fine ultimo e` dato dalla realizzazione di un esperimento risolto in tempo capace di utlizzare impulsi HHG circolarmente polarizzati per comprendere il processo di demagnetizzazione di sistemi ferromagnetici, sulla scala temporale del femtosecondo.
XXII Ciclo
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Risoud, François. "Theoretical study of attosecond dynamics in atoms and molecules using high-order harmonic generation as a self-probe." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066234/document.
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Dans cette thèse, j'ai étudié théoriquement l'interaction d'atomes et de molécules avec des impulsions laser brèves, intenses et basse-fréquences. En insistant sur la phase spectrale, nous utilisons la génération d'harmoniques d'ordres élevés comme processus auto-sonde pour étudier les dynamiques attoseconde. Nous résolvons l'équation de Schrödinger avec des modèles simples, numériquement ou en utilisant une théorie semi-analytique, nous permettant ainsi d'obtenir des informations approfondies sur les processus physiques mis en jeu, à travers des explications intuitives, tout en gardant une propension prédictive. Avec des outils développés pour analyser nos résultats numériques, nous étudions d'abord la dynamique d'ionisation dans une molécule modèle telle que N2. Puis, en réexaminant les interférences à deux centres, nous mettons au jour un comportement très intéressant, lié à l'habillage de l'état fondamental par le laser, et confirmé par des développements analytiques. Nous prédisons la possibilité d'observer ce phénomène expérimentalement par l'intermédiaire des interférences de chemins quantiques. Enfin, nous étudions les effets de la vibration des noyaux dans les molécules diatomiques en couplant le mouvement des électrons avec celui des noyaux. Nous montrons que pour de telles impulsions laser, l'excitation vibrationnelle de la molécule neutre peut être induite par effet Raman. Nous invalidons alors une théorie non corrélée, nommée Lochfraß, qui base son interprétation sur la dépendance du rendement d'ionisation avec la distance internucléaire. Enfin, nous proposons de prolonger à un modèle analytique standard la notion de potentiel d'ionisation dans les moléculesIn this thesis, I studied theoretically atoms and molecules interacting with a short, low-frequency and intense laser pulse, in the typical regime of high-order harmonic generation (HHG). We use HHG as a self-probe process to examine electronic and nuclear dynamics on the attosecond scale with Ångström resolution, insisting on the spectral phase. By using simple models, we are able to solve extensively the time-dependent Schrödinger equation, either numerically or with the Strong Field Approximation (SFA). Our models give us valuable physical insights on the underlying dynamical processes and intuitive explanations while keeping a predictive propensity. With efficient tools developed to analyze our numerical results, we first investigate the ionization dynamics through a shape resonance in a model molecule such as N2. Secondly, we take another look at two-center interferences, and uncover a very interesting behavior which is linked to the dressing of the electronic ground-state by the laser field. It is indeed confirmed by additional developments of molecular SFA. We predict that this behavior can be observed experimentally using quantum path interferences. Finally, we examine the effect of nuclear vibration in diatomic molecules by coupling consistently electronic and nuclear motions. Our results show that with short pulses, nuclear motion in the neutral molecule can be triggered by Raman effect. Thus, we invalidate an uncorrelated theory, so called Lochfraß, which focuses on the dependence of the ionization yield with internuclear distance as an explanation. Lastly, we question the extension within SFA of the notion of ionization potential in molecules
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Beaulieu, Samuel. "Probing femtosecond and attosecond electronic and chiral dynamics : high-order harmonic generation, XUV free induction decay, photoelectron spectroscopy and Coulomb explosion." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0063/document.
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Ce manuscrit de thèse s'articule autour de l'étude de l'interaction entre des impulsions lumineuses ultra brèves et des atomes ainsi que des molécules polyatomiques et chirales en phase gazeuse. En utilisant des techniques développées en physique attoseconde ainsi qu'en femtochimie, notre objectif général est de parvenir à une meilleure compréhension des dynamiques ultrarapides photoinduites dans la matière. Pour ce faire, nous avons développé des sources de lumière à ultra brèves dans le proche infrarouge et l’infrarouge moyen, qui ont été utilisées pour construire une source de rayons X dans la fenêtre de l’eau, basée surla génération d'harmoniques d’ordre élevé (GHOE), ainsi que pour l’étude de nouveaux canaux de GHOE impliquant des états hautement excités (Rydberg). Cette dernière étude a démontré une émission harmonique via l'ionisation depuis des états de Rydberg et la recombinaison radiative sur l'état fondamental, attirant ainsi notre intérêt pour le rôle des états de Rydberg en physique des champs forts. Cela nous a conduit à étudier la décroissance libre de l’induction XUV de paquets d'ondes électroniques comme une nouvelle technique de spectroscopie 2D. De plus, nous avons découvert que l'interaction entre un laser intense et un atome préparé dans une superposition cohérente d'états électroniques peut conduire à la génération de lignes hyper-Raman concomitantes avec la GHOE standard. Ce mécanisme avait été prédit lors des premiers calculs théoriques de GHOE, mais n'avait jamais été démontré expérimentalement. Par la suite, nous nous sommes intéressé à l’étude de systèmes moléculaires, dans lesquelles une excitation électronique induite par la lumière peut déclencher des dynamiques nucléaires. Nous avons étudié la photo isomérisation non-adiabatique de l’acétylène cationique en vinylidène cationique ainsi que le contrôle cohérent de la localisation électronique lors de la photodissociation de H2+. La simplicité de ces systèmes moléculaires a permis la comparaison des résultats expérimentaux avec des calculs théoriques de pointe,révélant l'importance du couplage entre les degrés de liberté nucléaires et électroniques lors de dynamiques moléculaires photoinduites.Un autre pilier majeur de cette thèse est l'étude de l'ionisation de molécules chirales avec des impulsions chirales. On sait depuis les années 70 que l'ionisation d'un ensemble de molécules chirales aléatoirement orientées, en utilisant une impulsion polarisée circulairement, conduit à une forte asymétrie avant-arrière dans le nombre de photoélectrons émis, selon l'axe de propagation de la lumière (DichroismeCirculaire de Photoélectron, DCPE). Avant cette thèse, le DCPE a été largement étudié à l’aide du rayonnement synchrotron (ionisation à un photon) et a récemment été démontré avec des lasers femtoseconde, via des schémas d'ionisation multiphotonique. Dans cette thèse, nous avons montré que le DCPE est un effet universel, c'est-à-dire qu'il émerge dans tous les régimes d'ionisation: l'ionisation àun photon, l'ionisation à multiphonique, l'ionisation au-dessus du seuil ainsi que l’ionisation par effet tunnel. Ensuite, nous avons démontré que la combinaison d’approches standard de femtochimie et du DCPE peuvent être utilisées pour suivre des dynamique de molécules chirales photoexcitées. En utilisant des approches expérimentales similaires, avec des séquences d'impulsions ayant des états de polarisation contre-intuitifs, nous avons démontré un nouvel effet chiroptique, appelé Dichroïsme Circulaire de Photoexcitation (DCPX), qui est décrit par un courant électronique directionnel et chirosensible, lorsque plusieurs niveaux sont peuplés de manière cohérente avec de la lumière chirale. Enfin, nous avons introduit une perspective temporelle à la photoionisation chirale en mesurant l'asymétrie avant arrièredes retards de photoionisation dans les molécules chirales photoionisées par des impulsions lumineuses chiralesThis thesis manuscript is articulated around the investigation of the interaction between ultrashort light pulses and gas-phase atoms, polyatomic and chiral molecules. Using the toolboxes developed in attosecond and strong-field physics as well as in femtochemistry, our general goal is to reach a better understanding of subtle effects underlying ultrafast light-induced dynamics in matter.To do so, we developed cutting-edge near-infrared and mid-infrared few-cycle light sources, which were used to build a water-window soft-X-ray source based on high order harmonic generation (HHG), as well as to study new HHG channels involving highly-excited (Rydberg) states. The latter study revealed a delayed HHG emission from the ionization of Rydberg states and radiative recombination onto the electronicground state, triggering our interest in the role of Rydberg states in strong-field physics. This led us to investigate the laser-induced XUV Free Induced Decay from electronic wave packets as a new background-free 2D spectroscopic technique.More over, we have found out that strong-field interaction with a well prepared coherent superposition of electronic states led to the generation of hyper-Ramanlines concomitant with standard high-order harmonics. These spectral features were predicted in the early-days theoretical calculations of HHG but had never been reported experimentally.After these experiments in rare gas atoms, we moved to molecular targets, in whichlight-induced electronic excitation can trigger nuclear dynamics. Using simple benchmark molecules, we have studied dynamics involving the participation of both nuclear and electronic degrees of freedom: first, we studied the ultrafast non adiabatic photoisomerization of the acetylene cation into vinylidene cation, andsecond, we investigated the coherent control of electron localization during molecular photodissociation of H2+. The simplicity of these molecular targets enabled the comparison of the experimental results with state-of-the-art theoretical calculations,revealing the importance of the coupling between nuclear and electronic degrees of freedom in photoinduced molecular dynamics.The other major pillar of this thesis is the study of ionization of chiral molecules usingchiral light pulses. It has been known since the 70s that the ionization from an ensemble of randomly oriented chiral molecules, using circularly polarized light pulse,leads to a strong forward-backward asymmetry in the number of emitted photoelectrons, along the light propagation axis (Photoelectron Circular Dichroism,PECD). Prior to this thesis, PECD was widely studied at synchrotron facilities (single photonionization) and had recently been demonstrated using table-top lasers in resonant-enhanced multiphoton ionization schemes. In this thesis, we have shownthat PECD is a universal effect, i.e. that it emerges in all ionization regimes, from single photon ionization, to few-photon ionization, to above-threshold ionization, up to the tunneling ionization regime. This bridges the gap between chiral photoionizationand strong-field physics. Next, we have shown how the combination of standard femtochemistry approaches and PECD can be used to follow the dynamics of photoexcited chiral molecules using time-resolved PECD. Using similar experimental approaches, but by using pulse sequences with counter-intuitive polarization states,we have demonstrated a novel electric dipolar chiroptical effect, called Photoexcitation Circular Dichroism (PXCD), which emerges as a directional and chirosensitive electron current when multiple excited bound states of chiral molecules are coherently populated with chiral light. Last, we introduced a time-domain perspective on chiral photoionization by measuring the forward-backward asymmetry of photoionization delays in chiral molecules photoionized by chiral light pulses. Our work thus carried chiral-sensitive studies down to the femtosecond and attosecond ranges
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Quintard, Ludovic. "Caractérisation et contrôle des profils spatiaux, spectraux et temporels de faisceaux XUV obtenus par génération d’harmoniques d’ordres élevés dans des gaz." Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0641/document.
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Dans ce travail nous présentons nos travaux réalisés sur le contrôle de la générationd’harmoniques d’ordres élevés dans les gaz. Dans un premiers temps nous montronscomment, en générant les harmoniques hors du foyer du faisceau IR, il est possiblede contrôler la phase spatiale des harmoniques dans le milieu générateur permettantd’obtenir un front d’onde divergent, collimaté ou convergent. Par cette méthode nousmontrons qu’il est possible de focaliser les harmoniques à des distances pouvant atteindresix longueur de Rayleigh après le point focal du faisceau IR. Nous avons ensuiteétudié des faisceaux harmoniques XUV présentant des distributions spatio-spectralesen champ lointain structurées. Dans cette étude nous observons l’influence d’un irisde diamètre variable positionné avant la focalisation de l’IR. Dans un troisième tempsnous étudions des méthodes de contrôle du spectre harmonique. Tout d’abord nousavons contrôlé finement la longueur d’onde centrale des harmoniques par modificationdu contenu spectral de l’IR en superposant deux impulsions IR retardées. Puis nousavons utilisé les effets collectifs de la génération d’harmoniques afin de favoriser uneharmonique spécifique ou un groupe d’harmoniques en champ lointain. Enfin, nousprésentons une méthode de caractérisation de la durée d’impulsions attosecondes dansle domaine temporel. Cette méthode, appelée ionisation par paliers, utilise l’ionisationcomme sonde pour mesurer des durée d’impulsions pouvant atteindre la centained’attosecondeWe present our work on the control of high order harmonic generation in gases.We first show how, by generating the harmonics outside the focus of the IR beam,it is possible to control the spatial phase of the harmonics in the generating mediumallowing to obtain a divergent, collimated or convergent wavefront. With this methodwe show that it is possible to focus the harmonics up to six Rayleigh length after thefocal point of the IR beam. Then we study XUV harmonic beams presenting structuredspacio-spectral distributions in the far field. In this study, we observe the influence ofthe diameter of an iris positioned before the focusing of the IR. In a third step we studymethods for controlling the harmonic spectrum. First, we finely control the harmonicscentral wavelength by modifiying the spectral content of the IR by adding two delayedIR pulses. Then we used the collective effects of the high order harmonic generationin order to foster a specific harmonic or a group of harmonics in the far field. Finally,we present a method for characterizing the duration of attosecond pulses in the timedomain. This method, called ionization ladder, uses ionization as a probe to measurepulse duration of up to hundreds of attosecond