Made available in DSpace on 2014-06-12T18:05:09Z (GMT). No. of bitstreams: 2 arquivo526_1.pdf: 2585524 bytes, checksum: ea4615447d3bce43a335c6515c2d06e7 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2009 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Nesta dissertação, investigamos experimentalmente a dinâmica da magnetização em filmes finos ferromagnéticos. Fazemos uso de um laser de pulsos ultracurtos de Ti:Safira para induzir a dinâmica coerente e observar sua evolução temporal através da técnica de excitação e sonda com dupla modulação. Uma discussão detalhada da técnica e o respectivo aparato experimental é apresentada tendo em vista que esta é sua primeira implantação em nosso laboratório. Realizamos medidas de magnetometria por efeito Kerr resolvida no tempo (Time-Resolved Magneto-Optical Kerr Efect: TR-MOKE) e observamos a magnetização transiente em filmes monocristalinos de ferro sobre óxido de magnésio (Fe/MgO) e de permalloy (Ni0:8Fe0:2) sobre silício (Py/Si). Os filmes foram preparados por sputtering e caracterizados por ressonância ferromagnética (FMR) pelo Grupo de Magnetismo do DF-UFPE. A anisotropia magnética verificada nestas amostras permitiu-nos estudar o seu papel na indução da dinâmica coerente por pulsos ultracurtos de laser. Os resultados obtidos mostram uma forte dependência da dinâmica com o campo de anisotropia.

Ce travail se place dans le cadre de la mesure ultrasensible d’anisotropie de phase optique que permet l’emploi adapté des cavités de très haute finesse. Pour stabiliser la fréquence laser sur une résonance de la cavité, un schéma d’asservissement reposant sur la rétroaction optique est utilisé.Une première partie décrit le couplage optique entre le laser et la cavité à travers l’analyse du comportement de la fréquence d’émission du laser auto-réinjecté. Une comparaison analytique théorie expérience a permis d’identifier les signaux d’erreur nécessaires au maintien durable de la fréquence du laser à l’exacte résonance d’un mode de la cavité. Après une description détaillée du dispositif d’asservissement, sa réalisation expérimentale sur une cavité de finesse de quelques milliers (F = 3 000)a démontré la possibilité de stabiliser la fréquence laser sur plus de dix heures avec une excursion résiduelle à la seconde de 375 Hz.Dans la deuxième partie, le développement précédent a été mis en œuvre sur une cavité de très haute finesse (F = 250 000) et a permis la mesure ultrasensible de biréfringence induite dans des gaz par effet Kerr. L’originalité du dispositif repose sur la mise à profit de la biréfringence résiduelle des miroirs de haute réflectivité.Elle est utilisée d’une part comme source à la rétroaction optique, et d’autre part comme biais optique à la mesure de la biréfringence du gaz. Une étude théorique et expérimentale détaillée des sources de bruit présent dans la chaîne de détection en fonction de la valeur du biais optique a permis de réaliser la mesure de déphasage au niveau du bruit de photons avec quelques mW de puissance laser. Ainsi, une sensibilité référence sur la mesure de déphasage Kerr de 3.10−13 rad a été démontrée pour un temps de mesure de 800 sec. Cette valeur record améliore de trois ordres de grandeur les déphasages Kerr précédemment mesurés. Le dispositif a été de plus mis à profit pour la mesure à faible champ électrique (< 40 V /mm) et à pression atmosphérique, des constantes de Kerr de différents gaz moléculaires et atomiques jusqu’à l’He. / The context of the work is the ultra-sensitive measurement of phase anisotropy permits by well-used of very high finesse cavity. To stabilize the laser frequency at the exact resonance of one cavity mode, a servo control based on optical feedback is used.In the first part, the optical coupling between laser and cavity is described through the comportment of the frequency of the self-locked laser. A comparison between experience and theory has permitted to identify the error signals in order to keep enduringly the laser frequency at the exact resonance. The experimental realization of the servo control into a 3 000 finesse cavity had demonstrated the stabilization of the laser frequency during more than ten hours with a residual one second excursion of 375 Hz.In the second part, the previous development has been used with a very high finesse cavity (F=250 000) to measure static Kerr birefringence in gases. The originality of the set-up is the use of the residual high reflectivity mirrors birefringence, firstly as the source of the optical feedback and secondly as an optical bias to measure the weak gas birefringence. An experimental and theoretical study of the noise according to the value of the optical bias has permitted a photon noise limited measurement (laser intensity of few mW). A record sensitivity of the phase shift induced by Kerr effect has been demonstrated at 3.10-13 rad with 800 s integration time. The scheme has been used to measure, in weak electric field (<40 V/mm) and in standard condition of pressure and temperature, the Kerr constant of molecular and atomic gases, even He gas

We show the scattering of electromagnetic radiation on a rotating cylinder and a rotating sphere using formalism of the vector spherical harmonics in this thesis. If a specific condition is satisfied then we can observe the rotational superradiance, phenomena originally discovered by Y. B. Zel'dovich in 1970s saying that the radiation can gain power by scattering on a rotating body. In this particular case there is an underlying principle of the rotational superradiance, the energy dissipation in the form of Joule heating created due to the induction of surface currents on the conductor. Superradiance can occur in the radiation scattering on the rotating black hole background, although there is no dissipation present. We summarize the results of scattering on the Kerr black hole from the literature, including an application called Black hole bomb, when the black hole is enclosed into a perfectly reflecting mirror. We show that for the lowest modes of the radiation at specific intervals the general relativity results can be approximated by scattering on the flat spacetime.

Canadian remembrance of the Great War (1914-1918) in the early twenty-first century is often associated with grand gestures at national monuments like the opening of the new Canadian War Museum in 2005 and the restoration of the Vimy Ridge Memorial in 2007. However, these sites of memory, what Pierre Nora terms lieux de mémoire, are not part of the everyday environments of memory, the milieux de mémoire, of most Canadians. In my investigation of three contemporary works of Canadian literature: The Danger Tree by David Macfarlane, Broken Ground by Jack Hodgins, and Unity (1918) by Kevin Kerr, locally-based storytellers describe the continued influence of the Great War on their individual Canadian communities. The fictionalized narrating personas in these three works create what I refer to as bio-geographies: first-person accounts of the narrator’s particular social and memory environments. While the bio-geographers in these three texts lack first-hand experience of the Great War, their writing reflects the continued repercussions of the conflict in the weeks, years, and decades after the 1918 armistice. The Great War differentially affected thousands of communities in Canada and Newfoundland. Constructing a coherent national narrative that accounts for the multiple lived experiences of individuals in communities across North America is virtually impossible. Turning to local representations of the Great War (in the case of the three bio-geographic texts: depictions of communities in Newfoundland, British Columbia, and Saskatchewan) provides a sense of the nation as a diverse landscape of memory with multiple vantage points. Negotiating the complex terrain of self, place, and memory, the bio-geographers in the three works I examine create representations of the past that reveal how sites of memory, lieux de mémoire, come to be firmly embedded in the ongoing lived experiences of comunity members, the milieux de mémoire. / Arts, Faculty of / English, Department of / Graduate

In this thesis we ran a series of 2D simulations of femtosecond laser pulses filamenting in air using the FDTD method, a saturable Lorentz oscillator model of air [1], and two separate models of plasma: a Drude model where the plasma density is static in space, and a particle-in-cell model where plasma is free to migrate throughout the simulation space. By comparing matched pairs of simulations, which varied in pulse size, duration, and intensity, we can gauge the impact plasma dynamics has upon the evolution of a filamenting laser pulse. From these tests we determine that, while there are some visible differences between dynamic and static plasmas, plasma dynamics do not significantly alter the evolution of the pulse.

Orientador: Antonio Vidiella Barranco / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-03T15:07:28Z (GMT). No. of bitstreams: 1 Melo_PauloSilva_M.pdf: 2434588 bytes, checksum: d385f55b65d683a4c9d2644625e43e54 (MD5) Previous issue date: 2003 / Resumo: No presente trabalho estudamos, como uma extensão de um sistema de poucos níveis, um sistema que consiste de um átomo de três níveis na configuração D interagindo com dois modos do campo de radiação. Supomos que o nível 2 esteja bem fora da ressonância e que será eliminado adiabaticamente, de modo que ele possa agir apenas como um estado virtual nas transições entre os níveis 1 e 3. Este é conhecido como modelo Raman acoplado. Derivamos o Hamiltoniano do sistema Raman acoplado através de uma transformação unitária. Investigamos a influência dos "Stark-shifts" e de um meio tipo Kerr na evolução dos subsistemas por meio da inversão atômica, do parâmetro Q de Mandel e da pureza dos subsistemas. Em particular investigamos a competição entre os efeitos dos "Stark-shifts" e do meio Kerr, buscando sob quais condições o átomo apresentaria evolução periódica, o que implica no desemaranhamento entre os estados atômico e dos campos / Abstract: In the present work we study, as an extension of few-level systems, a system which consists of a three-level atom in the D configuration interacting with two modes of the radiation field. The level 2 is assumed to be far off resonance and will be adiabatically removed so that it participates as a virtual state in the transitions between levels 1 and 3. This is the Raman-coupled model. We derive a Raman coupled Hamiltonian by a unitary transformation. We investigate the in uences of the "Stark-shifts" and the Kerr-like medium in the sub-systems by means of the atomic inversion, Mandel¿s Q parameter and the purity of the sub-systems. We investigate the competition between the effects of the "Stark-shifts" and the Kerr-like medium, looking for the conditions leading to atomic periodic evolution, which is related to the disentanglement between the atom and the fields / Mestrado / Física / Mestre em Física

Orientador: Antonio Vidiella-Barranco / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-03T15:39:51Z (GMT). No. of bitstreams: 1 Gomes_AlvaroFernandez_D.pdf: 1463180 bytes, checksum: e7afc315eaab1eeb818ae16a2027e1de (MD5) Previous issue date: 2003 / Resumo: A construção de estados puros do campo eletromagnético é importante não só para o estudo dos fundamentos da mecânica quântica, como a questão do estado gato de Schrõdinger, mas também possui um grande potencial de aplicação, como por exemplo, na computação quântica, na criptografia quântica e nas medidas de alta precisão. Nesta tese, apresentamos três propostas onde o ponto central é o estudo da transferência progressiva de coerência dos átomos para o campo eletromagnético, visando gerar um estado com um alto grau de purificação a partir de um estado de mistura estatística. Para isso utilizamos o micromaser com a interação átomo-campo dado pelo modelo Jaynes-Cummings de dois fótons. No primeiro trabalho consideramos os átomos inicialmente preparados em uma superposição coerente de dois estados (condição necessária para a transferência de coerência átomo-campo) e o campo na cavidade preparado em um estado mistura do. Primeiramente determinamos o melhor tempo de interação de cada átomo para que o estado do campo apresentasse o maior grau de purificação possível. Fixamos esse tempo para todos os átomos e determinamos o grau de pureza do estado final do campo, após N -átomos terem passado pela cavidade. Em nosso segundo trabalho acrescentamos à cavidade um meio não-Iinear tipo Kerr. Utilizando o mesmo procedimento do primeiro caso, obtivemos um menor tempo de interação átomo-campo e um grau de purificação maior para o estado do campo gerado na cavidade, em relação ao primeiro trabalho. Por último, acrescentamos um campo clássico externo interagindo com o átomo dentro da cavidade sem o meio Kerr. Novamente, com o mesmo procedimento dos trabalhos anteriores, verificamos que esse campo, além de influenciar na transferência de coerência átomo-campo, torna desnecessária a preparação dos átomos em uma superposição coerente de dois estados. Visando a caracterização do estado do campo final gerado, foram calculadas a função de coerência de segunda ordem e a quasiprobabilidade conhecida como a função de Husimi (ou função Q) / Abstract: The construction of pure states of the electromagnetic field is important not only for the study of the foundations of the quantum mechanics, such as the question of the Schrõdinger cat states, but also for its potential applications, for example, in quantum computation, quantum criptography and in higher precision measurements. In this thesis, we present three proposals where the central point is the study of the progressive transfer of coherence of atoms to the electromagnetic field, aiming the generation of a state with a higher degree of purity from a mixed state. For this we use the micromaser with the atom-field interaction given by the two-photon Jaynes-Cummings model. In our first work we initially consider atoms prepared in a coherent superposition of two states (necessary condition for the atom-field transfer of coherence) and the field in the cavity prepared in a mixed state. We determine the best interaction time for each atom so that the state of the field presents the highest possible degree of purification. We fix that time for all atoms and determine the degree of purity of the final state of the field, after N -atoms have crossed the cavity. In our second work we add to the cavity a nonlinear Kerr-like medium. Using the same procedure as in the first case, we obtain smaller atom-field interaction times as well as a higher degree of purification for the state of the field generated in the cavity, compared to the first work. Finally, we add an external classical field interacting with the atom inside the cavity without the Kerr medium. Again, with the same procedure of the previous works, we verify that the external field, besides influencing in the atom-field transfer of coherence turns unnecessary the preparation of atoms in a coherent superposition of two states. In order to characterize the state of the generated ( final) field, we have calculated the second order correlation function as well as the quasiprobàbility known as the Husimi function (or Q function) / Doutorado / Física / Doutor em Ciências

Kerr frequency combs enable compact and robust platforms for applications such as data communications and spectroscopy. Initial demonstrations used dissipative soliton combs operating in the anomalous group velocity dispersion (GVD) regime to illustrate the promising capabilities of Kerr-comb-based technologies. However, many real-world applications, such as wavelength division multiplexing and LiDAR, benefit from higher comb-line powers that are inherently inaccessible to Kerr frequency combs. Nevertheless, nonsolitonic Kerr combs operating in the normal GVD regime offer promise as a platform for the integration of such applications due to their ability to easily access high pump-to-comb conversion efficiencies and spectral profiles with slower power falloffs. Unlike a dissipative Kerr soliton which is a single cycle periodic pattern on top of a homogenous background, a nonsolitonic Kerr comb arises through the interlocking of two switching waves of opposite polarity, each of which connects the two homogenous state solutions of the bistable cavity response. Here, we present a systematic approach for turn-key generation of Kerr combs in the normal GVD regime. We use a coupled ring geometry to induce and control avoided mode crossings for the generation of low-noise frequency combs with conversion efficiencies of up to 57%. Moreover, we explore the regime of synchronization for these nonsolitonic Kerr combs. Synchronization is a universal mechanism of coupled nonlinear oscillators that manifests itself as the spontaneous appearance of order within nature's tendency for disorder and chaos. It is a process by which the natural rhythms of interacting oscillators adjust to a common frequency and produce a mutually phase-locked state. In the realm of Kerr frequency combs, synchronization allows for the repetition rates, or equivalently the comb-line spacings, of individual Kerr combs to become identical. We reveal the universality of Kerr comb synchronization by synchronizing two nonsolitonic Kerr combs and thereby extending the scope of synchronization beyond the soliton regime. Furthermore, we introduce a method to overcome the inherently low output power of Kerr combs while maintaining the high conversion efficiency of a normal GVD Kerr comb. We demonstrate efficient comb-line power enhancement by coherently combining two nonsolitonic Kerr combs via on-chip synchronization. Our on-chip synchronization design removes the requirement for dispersion compensation of the coupling signal while increasing the overall stability of the system. Our techniques of comb generation, synchronization, and coherent combining enable nonsolitonic Kerr combs as a platform to achieve a fully integrated, high-power Kerr comb source.

This doctoral dissertation focuses on the nonlinear optical response of water vapour as well as some solids at terahertz (THz) frequencies. In this study, the propagation of broadband single-cycle THz pulses through a medium with the third-order nonlinear optical response is theoretically investigated. Also, a technique to measure the nonlinear response of transparent materials based on the time-domain THz spectroscopy is developed, which provides frequency dispersion curves of the nonlinear Kerr coefficient (n₂). A numerical model is used to simulate the THz pulse propagation. This model takes into account non-paraxial effects, self-focusing, and diffraction, as well as dispersion, in both the linear and nonlinear optical regimes. The contribution of non-instantaneous Kerr-type nonlinearity to the overall instantaneous and delayed Kerr effect at the THz frequencies is investigated. It is shown how increasing the nonlinear relaxation time and its dispersion modifies the THz pulse after the propagation through a transparent medium. The effect of linear dispersion on self-action during pulse propagation is also discussed. Moreover, the nonlinear spectroscopy of water vapour at THz frequencies is reported. Atmospheric water vapour has a rich spectrum with several strong resonances at frequencies below 3 THz, falling within the range of operation of most existing THz sources. An extremely large nonlinear response to THz radiation is observed at the positions of these resonances. Using the optical Kerr model for the nonlinear response, a minimum nonlinear refractive index of the order of 10² m²/W is estimated. The results provide insight into the energy levels of the water molecule and give a more accurate picture of its response to electromagnetic radiation, paving the way to more accurate THz spectroscopy, imaging, and sensing systems, and thereby facilitating future emerging THz technologies. Finally, the nonlinear response of solids at THz frequencies is studied. It has been shown that a phonon-induced THz Kerr effect can result in a larger nonlinear refractive index than the nonlinear refractive index at the visible or near-infrared range (optical Kerr effect). This pronounced nonlinear optical behavior is verified using a time-domain characterization approach. The results indicate a large delay occurred to the THz fields as they transmit through some of the material samples. In the frequency domain, the induced nonlinear phase shift of the intense THz field is shown to be relatively large of the order of 0.1 rad. From the phase information, the nonlinear phase is extracted by which the dispersion profile of n₂ is obtained.

No description available.