Magnonika je novým odvětvím výzkumu, který se zabývá fyzikou spinových vln. Magnonika jako vědní obor nabízí nové možnosti například v nediskrétních výpočtech na základě vlnového charakteru spinových vln. Při výrobě magnonických prvků klasickými metodami není možné příliš měnit charakter materiálů, ze kterých jsou jednotlivé prvky vyrobeny. Tento fakt silně omezuje univerzálnost vyrobených struktur. Cílem této práce je aplikovat nový typ materiálu do oboru magnoniky. Specifikum daného materiálu je možnost zápisu magnetických struktur pomocí iontového svazku. Ukazuje se, že tyto struktury mají velice zajímavé magnetické vlastnosti, které lze velice přesně řídit právě strategií ozařování iontovým svazkem. Na základě fázově rozlišené Brillouinovy spektroskopie jsme získali disperzní relaci spinových vln v tomto systému a tím i důležité parametry systému. Pozorování podkládáme mikromagnetickými simulacemi a analytickými modely. Vlastnosti systému pro magnonické aplikace prezentujeme na třech prototypických sadách struktur, které nelze vyrobit pomocí klasických materiálů.

Increased complexity of novel magnetic materials in the last decade has placed high demands on the manufacturing process as well as on the characterization. One of the possibilities for characterization of magnetic samples is to exploit the magneto-optical effects. The presented work uses the magneto-optical Kerr effect as a major characterization technique to probe the magnetic properties of samples. We have developed a mathematical model describing the effect of the magnetization on the polarized light and present an apparatus capable of measuring the response given by the light-matter interaction. The experimental results show the performance of the apparatus on the various magnetic systems including meta-stable iron layers, Stoner-Wohlfarth particles and magnetic vortices. The scanning vectorial Kerr magnetometer allowed us to probe the vector of magnetization with diffraction limited resolution below 500 nm.

This thesis aims to explore the effect of in situ ion gun etching on magnetic proper- ties, such as perpendicular magnetic anisotropy, of Pt/Co/Pt multilayers. Perpendicular magnetic anisotropy is of interest due to its importance in spintronic application. Calibration spectroscopic ellipsometry measurements of Pt and Co layers to obtain sputter yields of respective magnetron targets were performed as a first step. After that, ten Pt/Co/Pt multilayers with different Co and top Pt layer thicknesses were prepared. Five of these samples were etched by the ion gun, mounted inside of the magnetron chamber, during different stages of the deposition. To characterize the prepared samples, experimental and modeled Kerr rotation spectra were confronted. This provided an insight into the cross-sections of the investigated samples. Magnetic hysteresis loops measured by vibrating sample magnetometer and Kerr rotation setup demonstrated higher coercive field and change of the slope of the loop induced by ion etching. When compared to the obtained cross-sections, a correlation between the change of magnetic loops and intermixing of Pt and Co at the interface was visible. This intermixing was higher in samples treated by the ion gun. 1

No description available.

This thesis examines second-order optical nonlinear wave mixing processes in domain-disordered quasi-phase matching waveguides and evaluates their potential use in compact, monolithically integrated wavelength conversion devices. The devices are based on a GaAs/AlGaAs superlattice-core waveguide structure with an improved design over previous generations. Quantum-well intermixing by ion-implantation is used to create the quasi-phase matching gratings in which the nonlinear susceptibility is periodically suppressed. Photoluminescence experiments showed a large band gap energy blue shift around 70 nm after intermixing. Measured two-photon absorption coefficients showed a significant polarization dependence and suppression of up to 80% after intermixing. Similar polarization dependencies and suppression were observed in three-photon absorption and nonlinear refraction. Advanced modeling of second-harmonic generation showed reductions of over 50% in efficiency due to linear losses alone. Self-phase modulation was found to be the dominant parasitic nonlinear effect on the conversion efficiency, with reductions of over 60%. Simulations of group velocity mismatch showed modest reductions in efficiency of less than 10%. Experiments on second-harmonic generation showed improvements in efficiency over previous generations due to low linear loss and improved intermixing. The improvements permitted demonstration of continuous wave second-harmonic generation for the first time in such structures with output power exceeding 1 µW. Also, Type-II phase matching was demonstrated for the first time. Saturation was observed as the power was increased, which, as predicted, was the result of self-phase modulation when using 2 ps pulses. By using 20 ps pulses instead, saturation effects were avoided. Thermo-optically induced bistability was observed in continuous wave experiments. Difference frequency generation was demonstrated with wavelengths from the optical C-band being converted to the L- and U-bands with continuous waves. Conversion for Type-I phase matching was demonstrated over 20 nm with signal and idler wavelengths being separated by over 100 nm. Type-II phase matched conversion was also observed. Using the experimental data for analysis, self-pumped conversion devices were found to require external amplification to reach practical output powers. Threshold pump powers for optical parametric oscillators were calculated to be impractically large. Proposed improvements to the device design are predicted to allow more practical operation of integrated conversion devices based on quasi-phase matching superlattice waveguides.

Ce travail porte sur l’exaltation de l’effet magnéto-optique (MO) Kerr transverse induite par des «résonances extraordinaires» dans un réseau d’or périodique 1D déposé sur un oxyde de grenat magnéto-optique. La structure complète incluant le réseau métallique 1D a été conçue, simulée numériquement, dimensionnée, fabriquée puis caractérisée. Un algorithme de type RCWA (Rigorous Coupled Wave Algorithm) adapté au calcul parallèle a été développé et utilisé d’une part pour l’étude théorique des modes résonants dans les réseaux magnétoplasmoniques et d’autre part pour l’analyse des données de mesures optiques et magnéto-optiques d’ellipsométrie à base de matrices de Mueller. L’impact sur la réflectivité angulo-spectrale du couplage entre les modes Fabry-Pérot des fentes du réseau et les plasmons de surface à l’interface entre l’or et la couche de grenat MO est ainsi étudié, en utilisant les paramètres optiques et magnéto-optiques réels des matériaux. Pour cela, les caractéristiques optiques du substrat en sGGG (grenat de gallium et gadolinium dopé CaMgZr) et du matériau Bi:GIG (grenat de fer et de gadolinium substitué bismuth) sont au préalable déterminés dans la gamme spectrale 0,73 – 6,42 eV (193 nm-1,7 μm) par ellipsométrie à base de matrices de Mueller. Puis de même la dispersion des composantes magnéto-optiques du tenseur diélectrique est obtenue en appliquant un champ magnétique externe dans le plan, en configuration longitudinale ou transverse. Ces données mesurées sont alors utilisées dans les simulations. Il est ainsi démontré numériquement que grâce à l’interaction des résonances de surface et de cavité dans le réseau 1D l’effet Kerr transverse peut être exalté, éteint ou même de signe inversé, et cela sans renverser ou modifier l’aimantation de la couche magnéto-optique. Pour confirmer les résultats théoriques, une série d’échantillons comportant des réseaux de fentes différentes a été fabriquée par lithographie électronique et procédé de lift-off. Afin de reproduire les données des matrices de Mueller mesurées, les modèles ont été adaptés et optimisés pour tenir compte des imperfections des structures réelles. Les mesures expérimentales confirment l’exaltation de l’effet Kerr magnéto-optique transverse due aux effets magnéto-plasmoniques et prouvent la validité des modèles. / This work studies the enhancement of the transverse magneto-optical Kerr effect by exploiting extraordinary resonances occurring in 1D periodic grating. The 1D periodic gold grating structure was designed, described, numerically simulated, and fabricated. A rigorous Coupled Wave Algorithm (RCWA) developed for parallel computing is used for the theoretical study of resonant modes in magnetoplasmonic gratings and for analysis of optical and magneto-optical data measured by Mueller matrix ellipsometry. The impact of coupling between Fabry-Perot modes inside grating air-gaps and surface plasmon mode at the interface between gold and MO garnet layer is studied via spectra of specular reflectivity and for the various angles of incidence. In a first step, the optical functions of the (CaMgZr)-doped gallium-gadolinium garnet (sGGG) substrate and the Bi-substituted gadolinium iron garnet (Bi:GIG) are obtained in the spectral range from 0.73 eV to 6.42 eV (wavelength range 193 nm – 1.7 μm). Subsequently, the spectra of the magneto-optical tensor components are obtained by applying an external in-plane magnetic field in longitudinal and transverse geometry. The obtained functions are then used for numerical simulations demonstrating that by hybridization of surface and cavity resonances in this 1D plasmonic grating, the transverse Kerr effect can be further enhanced, extinguished or even switched in sign and that without inverting or modifying the film's magnetization. To confirm theoretical results a set of samples, gratings with a different width of an air-gap, was fabricated using electron beam lithography and liftoff technique. To be able to reproduce Mueller matrix data from the samples, the models describing realistic structures were further developed and optimized. Experimental measurements of real structures confirm transverse MO effect enhancement using magnetoplasmonic effects and prove applicability of numerical models.

Chaque faisceau d'un laser de puissance, tel que le Laser MégaJoule, est mis en forme et voit son énergie amplifiée à l’aide d’une centaine de composants optiques tels que des plaques de verre amplificateur, des lentilles, des miroirs, des lames de phase, des réseaux... 'Evidemment ces composants ne sont pas parfaitement réalisés et ils présentent à leurs surfaces des défauts de fabrication. Ces imperfections peuvent être dues aux outils de polissage des composants, aux dépôts antireflet ou même apparaitre au cours de la phase d’exploitation ou de remédiation du composant. Ces défauts contribuent à une baisse des performances du Laser MégaJoule que ce soit au niveau de l’énergie déposée au centre de la chambre d’expériences ou à l’endommagement accéléré des composants optiques placés en aval. Actuellement la norme ISO 10110-7 est utilisée pour spécifier les défauts d’aspect. Cependant elle manque de justification pour les besoins d’une chaine laser de puissance. Dans le cadre de la thèse nous nous intéressons exclusivement à l’endommagement fratricide local des composants optiques. Un défaut présent à la surface du composant module l’onde lumineuse par phénomène de diffraction. Un << point chaud >> peut apparaitre dans le faisceau laser augmentant alors la densité locale surfacique d’énergie appliquée aux composants suivants. La loi d’endommagement prédit une augmentation de la probabilité d’endommagement puisque la densité d’énergie est modifiée. Une première étude, fondée sur les équations de Fresnel, met en évidence les paramètres intéressants à spécifier pour prédire les intensifications engendrées par des défauts typiques. Le lien entre paramètres du défaut et intensifications diffractées est, ensuite, validité expérimentalement sur des cas réels de défauts. Une seconde étude établit un seuil exprimé en puissance en deçà duquel l'hypothèse d'une propagation linéaire, selon les équations de Fresnel, est valide. La cohérence des résultats donnés par le seuil en puissance et par la simulation numérique renforce l’idée voulant que la propagation d’un << point chaud >> en présence d'effet Kerr soit sensiblement différente de celle d’un faisceau gaussien. Fort de ces deux résultats nous sommes en capacité d'établir une spécification des défauts d’aspect en ayant une meilleure compréhension de l’endommagement fratricide local. / Each beam of a high power laser facility, such as the Laser MégaJoule, is shaped and amplified thanks to hundreds optical components such as amplifier slabs at Brewster’s angle, lenses, mirrors, phase plates, diffraction gratings... Of course, all these components cannot be perfect; there are some defects on their surface. These imperfections appear at each stage of the life of the component, during polishing, coating, or mitigation process or when the component is used on the facility. They have a huge impact on the energy losses delivered on the target and they decrease the resistance of downstream components to intense light. The ISO 10110-7 standard is currently used to specify the visual defects. However, this standard is poorly justified and do not fit a high power laser needs. In this thesis, we are focused on the fratricide effect. Light propagates through a defect, then, some intensity modulations appear along the propagation. The damage law states that high energy density leads to an increase of the damage probability. Firstly, we investigate the characteristic parameters of the defect morphology linked to the formation of downstream << hot spots >>. Then, the link between these typical parameters and the high intensifications are confirmed by experiments on real defects. Secondly, a power criterion is demonstrated to guarantee the linear propagation hypothesis. This criterion is compared to numerical simulations and it is shown how the nonlinear propagation, induced by Kerr effect, can be different between the << hot spot >> formed by a defect and a Gaussian beam. Finally, the results are used to improve the visual defect specification thanks to a better understanding of the fratricide effect.

Magneto-optical materials such as permalloy can be used to create artificial spin- ice (ASI) lattices with antiferromagnetic ordering. Magneto-optical materials used to create diffraction lattices are known to exhibit magnetic scattering at the half- order Bragg peak while in the ground state. The significant drawbacks of studying the magneto-optical generation of OAM using x-rays are cost, time, and access to proper equipment. In this work, it is shown that the possibility of studying OAM and magneto-optical materials in the spectrum of visible light at or around 2 eV is viable. Using spectroscopic ellipsometry it is possible to detect a change in the magnetization of thin permalloy films with thicknesses between 5 and 20 nm. Patterns consistent with OAM were found at 1.95 eV using a square lattice with a 4𝜋 radial phase shift in the antiferromagnetic ground state. Evidence of magnetic scattering at the half-order Bragg peak using 1.95 eV was also found.

This thesis examines second-order optical nonlinear wave mixing processes in domain-disordered quasi-phase matching waveguides and evaluates their potential use in compact, monolithically integrated wavelength conversion devices. The devices are based on a GaAs/AlGaAs superlattice-core waveguide structure with an improved design over previous generations. Quantum-well intermixing by ion-implantation is used to create the quasi-phase matching gratings in which the nonlinear susceptibility is periodically suppressed. Photoluminescence experiments showed a large band gap energy blue shift around 70 nm after intermixing. Measured two-photon absorption coefficients showed a significant polarization dependence and suppression of up to 80% after intermixing. Similar polarization dependencies and suppression were observed in three-photon absorption and nonlinear refraction. Advanced modeling of second-harmonic generation showed reductions of over 50% in efficiency due to linear losses alone. Self-phase modulation was found to be the dominant parasitic nonlinear effect on the conversion efficiency, with reductions of over 60%. Simulations of group velocity mismatch showed modest reductions in efficiency of less than 10%. Experiments on second-harmonic generation showed improvements in efficiency over previous generations due to low linear loss and improved intermixing. The improvements permitted demonstration of continuous wave second-harmonic generation for the first time in such structures with output power exceeding 1 µW. Also, Type-II phase matching was demonstrated for the first time. Saturation was observed as the power was increased, which, as predicted, was the result of self-phase modulation when using 2 ps pulses. By using 20 ps pulses instead, saturation effects were avoided. Thermo-optically induced bistability was observed in continuous wave experiments. Difference frequency generation was demonstrated with wavelengths from the optical C-band being converted to the L- and U-bands with continuous waves. Conversion for Type-I phase matching was demonstrated over 20 nm with signal and idler wavelengths being separated by over 100 nm. Type-II phase matched conversion was also observed. Using the experimental data for analysis, self-pumped conversion devices were found to require external amplification to reach practical output powers. Threshold pump powers for optical parametric oscillators were calculated to be impractically large. Proposed improvements to the device design are predicted to allow more practical operation of integrated conversion devices based on quasi-phase matching superlattice waveguides.

Title: Magnetic nanostructures for recording and optical sensors Author: Eva Lišková Department: Institute of Physics, Charles University Supervisor: Prof. Ing. Štefan Višňovský, DrSc. Abstract: Magneto-optical (MO) spectra of multilayered structures with enhanced MO effect were studied using the polar and longitudinal Kerr spectroscopy with oblique angle of light incidence in the photon energy range 1.2 eV to 5 eV. The samples with Fabry- Perot cavity like architecture, were modeled using Yeh matrix formalism. Two sets of samples, with composition FeF2/Fe/FeF2 and AlN/Fe/AlN, were prepared by molecular beam epitaxy and sputtering. The relations were studied between the position of the enhanced peak in the MO spectra and the structure. Second part of this work was devoted to the Pt/Co/Pt structures and the influence of the ion implantation on MO spectra and structural composition. The studied multilayer structures present interest for MO sensor and memory applications. Keywords: Magneto-optical Kerr effect, Magneto-optical sensor, Fabry-Perot resonator, Ion implantation