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Uppsala University

1. Valgeborg, Fredrik Stångberg. Element-Specific Magnetization Dynamics Using T-MOKE at the HELIOS Laboratory.

Degree: Molecular and condensed matter physics, 2016, Uppsala University

Magnetism is a familiar phenomenon, and is applied in a variety of devices, from simple ones, like compasses, to the more sophisticated magnetic hard disk drives. It is also known that the magnetization of a material can change, for example by heating or by exposure to an external magnetic field. The dynamics of transitions between different magnetizations, however, is largely unknown, particularly in complex materials. To further the understanding of such dynamics, this thesis presents an observational study of the dynamics of laser induced demagnetization of permalloy (Ni0.8Fe0.2). Dynamics were studied with element-specificity, i.e. Fe and Ni were studied simultaneously, but separately, rather than studying the overall material. The study was conducted at the HELIOS laboratory at Uppsala University, which features equipment for the study of magnetization dynamics. Important concepts like high-order harmonic generation (HHG) and the transverse magneto-optic Kerr effect (T-MOKE) are discussed. HHG is the laser induced generation of high energy photons, and T-MOKE relates the intensity of reflected light to the magnetization of the reflecting material. The study revealed a very short demagnetization time, and maximum demagnetization of both elements was achieved within 1 picosecond. An onset delay in the demagnetizations of Fe and Ni of about 25 femtoseconds was also observed. Both phenomena have been previously reported. The results further imply that the magnetizations diverge over a 10 picosecond time interval after the onset of demagnetization, which has not been previously reported. The apparent divergence may be due to an unknown transient setup-related issue. The short demagnetization times, as well as the onset delay could potentially contribute to the development of a more complete theory of magnetization dynamics.

Magnetism är ett bekant fenomen, som utnyttjas i allt från enkla tillämpningar, som kompasser,till mer sofistikerade sådana, som hårddiskar. Det är också känt att magnetiseringen i ett material kan ändras, t.ex. genom upphettning eller genom att det utsätts för ett yttremagnetiskt fält. Dynamiken vid övergångar mellan olika magnetiseringstillstånd är dock ett relativt okänt ämne, i synnerhet när det kommer till komplexa material. För främjandet av en större förståelse inom ämnet, presenteras här en observationell studie av dynamiken för laserinducerad avmagnetisering av permalloy (Ni0.8Fe0.2). Dynamiken undersöktes med grundämnesspecificitet, d.v.s. Fe och Ni undersöktes samtidigt, men var för sig, snarare än att materialet undersöktes som helhet. Undersökningen gjordes vid HELIOS-laboratoriet vid Uppsala Universitet, som tillhandahåller utrustning för undersökning av magnetiseringsdynamik. Viktiga koncept diskuteras, såsom övertonsgenerering och den transversella magnetooptiska Kerr-effekten (T-MOKE). Övertonsgenerering innebär laserinducerad generering av högenergifotoner, och T-MOKE relaterar reflekterad intensitet till…

Subjects/Keywords: magnetization dynamics; magnetization; demagnetization; magnetism; element-specific; element-specificity; T-MOKE; MOKE; pump-prob; time-resolved pump-probe; HHG; high-order harmonic generation; overtone generation; HELIOS; magnetiseringsdynamik; magnetisering; avmagnetisering; magnetism; grundämnesspecifik; grundämnesspecificitet; T-MOKE; MOKE; pump-prob; tidsupplöst pump-prob; HHG; övertonsgenerering; HELIOS

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Valgeborg, F. S. (2016). Element-Specific Magnetization Dynamics Using T-MOKE at the HELIOS Laboratory. (Thesis). Uppsala University. Retrieved from http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-297598

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Valgeborg, Fredrik Stångberg. “Element-Specific Magnetization Dynamics Using T-MOKE at the HELIOS Laboratory.” 2016. Thesis, Uppsala University. Accessed May 09, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-297598.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Valgeborg, Fredrik Stångberg. “Element-Specific Magnetization Dynamics Using T-MOKE at the HELIOS Laboratory.” 2016. Web. 09 May 2021.

Vancouver:

Valgeborg FS. Element-Specific Magnetization Dynamics Using T-MOKE at the HELIOS Laboratory. [Internet] [Thesis]. Uppsala University; 2016. [cited 2021 May 09]. Available from: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-297598.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Valgeborg FS. Element-Specific Magnetization Dynamics Using T-MOKE at the HELIOS Laboratory. [Thesis]. Uppsala University; 2016. Available from: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-297598

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation


University of Lund

2. Wikmark, Hampus. Spatial and temporal aspects of intense attosecond pulses for pump-probe experiments.

Degree: 2019, University of Lund

Nuclear and electronic dynamics in atoms and molecules are the foundation of many physical processes and chemical reactions. Often, these dynamics take place on timescales so much shorter than those commonly encountered that they are called ultrafast. In order to study ultrafast phenomena, time-resolved techniques such as pump-probe experiments, involving ultrafast light pulses, are necessary. For these experiments to be successful, the properties of ultrafast light pulses must be carefully controlled and examined in order to discern their influence on the experiment. This thesis deals with the spatial and temporal properties of XUV light, generated through the process of high-order harmonic generation in gases, using an intense IR laser beam. The influence of the spatial properties of this generating laser on the XUV has been studied, as has the influence of the XUV light's spatial properties on its focusability and peak intensity. The generated high-order harmonics are also used to study physical phenomena such as multiphoton ionization, something that requires high intensities. An instrument for simultaneous studies of ions and electrons produced by photoionization is also presented. The efforts towards ultrafast pump-probe experiments include designs for interferometer setups to enable these experiments. Some preliminary results of interferometer testing are also given, including a proof of principle of XUV-IR pump-probe experiments on the Lund Laser Centre intense XUV beamline.

Subjects/Keywords: Atom and Molecular Physics and Optics; Other Engineering and Technologies not elsewhere specified; ultrafast lasers; ultrafast optics; attosecond pulses; pump-probe experiments; XUV light; XUV focusing; wavefront sensing; XUV optics; X-ray optics; Fysicumarkivet A:2019:Wikmark; ultrasnabba lasrar; attosekundspulser; pump-prob-experiment; XUV-ljus; vågfrontmätningar; XUV-optik; Röntgen-optik

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Wikmark, H. (2019). Spatial and temporal aspects of intense attosecond pulses for pump-probe experiments. (Doctoral Dissertation). University of Lund. Retrieved from https://lup.lub.lu.se/record/e0078770-83c9-4201-9787-93a35ad76bb3 ; https://portal.research.lu.se/ws/files/62889948/Hampus_Wikmark_web.pdf

Chicago Manual of Style (16th Edition):

Wikmark, Hampus. “Spatial and temporal aspects of intense attosecond pulses for pump-probe experiments.” 2019. Doctoral Dissertation, University of Lund. Accessed May 09, 2021. https://lup.lub.lu.se/record/e0078770-83c9-4201-9787-93a35ad76bb3 ; https://portal.research.lu.se/ws/files/62889948/Hampus_Wikmark_web.pdf.

MLA Handbook (7th Edition):

Wikmark, Hampus. “Spatial and temporal aspects of intense attosecond pulses for pump-probe experiments.” 2019. Web. 09 May 2021.

Vancouver:

Wikmark H. Spatial and temporal aspects of intense attosecond pulses for pump-probe experiments. [Internet] [Doctoral dissertation]. University of Lund; 2019. [cited 2021 May 09]. Available from: https://lup.lub.lu.se/record/e0078770-83c9-4201-9787-93a35ad76bb3 ; https://portal.research.lu.se/ws/files/62889948/Hampus_Wikmark_web.pdf.

Council of Science Editors:

Wikmark H. Spatial and temporal aspects of intense attosecond pulses for pump-probe experiments. [Doctoral Dissertation]. University of Lund; 2019. Available from: https://lup.lub.lu.se/record/e0078770-83c9-4201-9787-93a35ad76bb3 ; https://portal.research.lu.se/ws/files/62889948/Hampus_Wikmark_web.pdf

3. Lakehal, Massil. Out of Equilibrium Lattice Dynamics in Pump Probe Setups : Dynamique hors équilibre du réseaux dans les expériences pompe-sonde.

Degree: Docteur es, Physique, 2020, Université de Paris (2019-....)

L'étude de la dynamique hors équilibre des systèmes fortement corrélés, à l'aide de laser femtoseconde, a révélé une variété de phénomènes sans analogue en physique d'équilibre. Dans cette thèse, nous étudions théoriquement la dynamique hors équilibre des degrés de liberté du réseau et leur signature en spectroscopie pompe-sonde. Nous développons une description microscopique des phonons cohérents displacive excité par le laser. La théorie capture la rétroaction de l'excitation des phonons sur le fluide électronique, qui manque dans la formulation phénoménologique actuelle. Nous montrons que cette rétroaction conduit à une oscillation avec une fréquence qui dépend du temps aux temps courts, même si le mouvement des phonons est harmonique. Pour les temps longs, cette rétroaction apparaît comme une phase résiduelle dans le signal oscillatoire. Nous appliquons la théorie au BaFe2As2, nous expliquons l'origine de la phase du signal oscillatoire rapporté dans des expériences récentes, et nous prédisons que le système oscille avec une fréquence décalé vers le rouge pour les grandes fluences. Notre théorie ouvre également la possibilité d'extraire des informations d'équilibre à partir la dynamique des phonons cohérents. Un autre phénomène intéressant qui a été observé en spectroscopie pompe-sonde est l'oscillation des fluctuations du réseau au double de la fréquence d’un phonon du système étudié. Ces oscillations sont interprétées comme une signature d'états de phonons squeezé macroscopique. Dans ce travail, nous identifions d'autres mécanismes d'oscillations à une fréquence double autre que le squeezing. Nous montrons qu'un quench de la température du bain thermique induite par la pompe, à laquelle le phonon est couplé, ou l'excitation d'un phonon cohérent pour lequel l'anharmonicité cubique est permise par symétrie peut également produire de telles oscillations en spectroscopie sans que le phonon soit dans un état squeezé. Nous concluons que, contrairement à ce qui est communément admis, les oscillations à double fréquence phononique en spectroscopie de bruit ne sont pas nécessairement une signature des phonons squeezés. Nous soulignons ce qui peut être un critère fiable pour identifier un phonon squeezé en utilisant la spectroscopie pompe-sonde.

The study of the out of equilibrium dynamics of strongly correlated systems, using ultrafast pulses, uncovered a plethora of phenomena with no analog in equilibrium physics. In this thesis, we theoretically investigate the out of equilibrium dynamics of the lattice degrees of freedom and their signature in pump-probe spectroscopy. We develop a Hamiltonian-based microscopic description of laser pump induced displacive coherent phonons. The theory captures the feedback of the phonon excitation upon the electronic fluid, which is missing in the state-of-the-art phenomenological formulation. We show that this feedback leads to chirping at short timescales, even if the phonon motion is harmonic. At long times, this feedback appears as a finite phase in the oscillatory signal. We…

Advisors/Committee Members: Paul, Indranil (thesis director).

Subjects/Keywords: Spectroscopie Pompe-Sonde; Electron phonon; Excitation displacive des phonons cohérent; Interaction des phonons cohérents; Phonon squeezé; Quench thermique; Électrons fortement corrélés; Formalisme de Keldysh; Pump-prob spectroscopy; Electron phonon; DECP; Coherent-phonons interaction; Squeezed phonon; Thermal quench; Strongly correlated electrons; Keldysh formalism

pump-probe setups. This thesis is dedicated to the theoretical investigation of the out of… …equilibrium lattice dynamics induced by an ultrafast pump-pulse. In chapter 1 and chapter 3, we… …dynamics. In the late decades, noise spectroscopy in pump-probe setups has become a powerful tool… …fluctuation driven by the ultrashort pump-pulse, and are invariably interpreted as signatures of… …the lattice in pump-probe setups. We identify two such mechanisms of 2ω oscillations that do… 

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Lakehal, M. (2020). Out of Equilibrium Lattice Dynamics in Pump Probe Setups : Dynamique hors équilibre du réseaux dans les expériences pompe-sonde. (Doctoral Dissertation). Université de Paris (2019-....). Retrieved from http://www.theses.fr/2020UNIP7039

Chicago Manual of Style (16th Edition):

Lakehal, Massil. “Out of Equilibrium Lattice Dynamics in Pump Probe Setups : Dynamique hors équilibre du réseaux dans les expériences pompe-sonde.” 2020. Doctoral Dissertation, Université de Paris (2019-....). Accessed May 09, 2021. http://www.theses.fr/2020UNIP7039.

MLA Handbook (7th Edition):

Lakehal, Massil. “Out of Equilibrium Lattice Dynamics in Pump Probe Setups : Dynamique hors équilibre du réseaux dans les expériences pompe-sonde.” 2020. Web. 09 May 2021.

Vancouver:

Lakehal M. Out of Equilibrium Lattice Dynamics in Pump Probe Setups : Dynamique hors équilibre du réseaux dans les expériences pompe-sonde. [Internet] [Doctoral dissertation]. Université de Paris (2019-....); 2020. [cited 2021 May 09]. Available from: http://www.theses.fr/2020UNIP7039.

Council of Science Editors:

Lakehal M. Out of Equilibrium Lattice Dynamics in Pump Probe Setups : Dynamique hors équilibre du réseaux dans les expériences pompe-sonde. [Doctoral Dissertation]. Université de Paris (2019-....); 2020. Available from: http://www.theses.fr/2020UNIP7039

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