In the present quantum optics and laser physics study, the non-linear interaction of electromagnetic fields with atomic, molecular and biomolecular media is analyzed. Particular emphasis is given to coherent phenomena, while propagation and dispersion effects are also extensively investigated. The fields involved vary from ultra short pulses to continuous waves; while their energies range from the very strong that are addressed classically, to the very weak which are described quantum mechanically. Applications and problems addressed span a wide range. A scheme for a real time detector of chemical and biological hazards, like anthrax spores, is presented; in it, a strong spectroscopic signature is obtained from complex molecules by using ultrashort, femtosecond, laser pulses and inducing vibrational coherence on them. Furthermore, a way of reversing the phase matching condition in coherent spectroscopy, based on dispersion, is developed; which allows for the use of such spectroscopic methods in remote detection. More fundamental questions addressed include a resolution of the centennial old paradox of Maxwell's demon via quantum thermodynamics, and the role of atomic coherence in enhancing the efficiency of a heat engine as well as in obtaining lasing without population inversion. Additionally, a quantum storage scheme is presented, in which the information contained in an optical pulse is stored and restored via photon echoes.

Nonlinear magneto-optical effects, originated from atomic coherence, are studied both theoretically and experimentally in thermal Rb vapor. The analytical description of the fundamental properties of coherent media are based on the simplified three- and four-level systems, and then verified using numerical simulations and experimental measurements. In particular, we analyze the modification of the long-lived atomic coherence due to various physical effects, such as reabsorption of spontaneous radiation, collisions with a buffer gas atoms, etc. We also discuss the importance of the high-order nonlinearities in the description of the polarization rotation for the elliptically polarized light. The effect of self-rotation of the elliptical polarization is also analyzed. Practical applications of nonlinear magneto-optical effects are considered in precision metrology and magnetometery, and for the generation of non-classical states of electromagnetic field.

Dans cette thèse, nous étudions les effets cohérents associés à la propagation d’ondes dans les milieux diffusants, en particulier les ondes électromagnétiques.En milieux faiblement désordonnés, l'intensité lumineuse fluctue spatialement sur de grandes distances. Ce phénomène est le résultat d'effets cohérents mésoscopiques complexes, qui se produisent à une échelle microscopique. Nous montrons que ces fluctuations mésoscopiques cohérentes de la lumière induisent des forces de rayonnement d'un nouveau genre. L'amplitude de ces forces fluctuantes est déterminée par un paramètre unique et facilement réglable, la conductance adimensionnée, qui dépend à la fois de la géométrie et des propriétés de diffusion du milieu. Notre découverte devrait donc avoir des applications intéressantes, telles que de nouveaux capteurs pour la matière molle ou la biophysique.Du point de vue méthodologique, nous utilisons une approche à la Langevin pour décrire les fluctuations lumineuses cohérentes, où un bruit précisément calculé rend compte des effets cohérents mésoscopiques. Nous montrons comment inclure systématiquement les corrections cohérentes dans le terme de bruit, afin de reproduire les fluctuations d'intensité. Cette description permet de comprendre les fluctuations cohérentes comme résultant d’un flux lumineux hors équilibre, caractérisé par deux paramètres seulement, le coefficient de diffusion et la mobilité, qui sont par ailleurs liés par une relation d’Einstein. Un avantage évident de cette méthode est sa dépendance à deux paramètres seulement, ce qui fournit une description à la fois compacte et précise des riches effets cohérents sous-jacents. De plus, la correspondance que nous présentons entre la lumière cohérente et l'hydrodynamique hors d'équilibre est facilement généralisable à une large classe de problèmes d'ondes quantiques ou classiques.Pour les perspectives futures, cette connexion entre les effets cohérents mésoscopiques et les processus stochastiques hors équilibre devraient intéresser les communautés de la mésoscopie et de la mécanique statistique. Pour les premiers, le lien avec l'hydrodynamique hors équilibre fournit un nouvel éclairage sur la physique mésoscopique, ainsi que des outils utiles pour étudier les quantités jusqu'ici difficiles d'accès, telles que les fonctions de corrélation d'intensité d'ordres supérieurs. Pour les seconds, ces travaux devraient motiver une étude plus approfondie des processus indépendants du temps inspirés de la mésoscopie. / In this work, we study coherent effects associated to wave propagation in scattering media, in particular electromagnetic waves.In weakly disordered media, light intensity fluctuates spatially over large distances. This phenomenon is the result of complex mesoscopic coherent effects, which occur at a microscopic scale. We show that these mesoscopic coherent fluctuations of light induce radiation forces of a new kind. The strength of these fluctuating forces is determined by a single and easily tunable parameter, the dimensionless conductance, which depends on both the geometry and the scattering properties of the medium. Our findings should therefore have interesting applications such as new sensors in soft condensed matter or biophysics.On the methodological viewpoint, we use a hydrodynamic Langevin approach to describe the coherent light fluctuations, where a properly tailored noise accounts for mesoscopic coherent effects. We show how to systematically include the coherent corrections in the noise term, in order to reproduce the intensity fluctuations. This description allows to understand coherent light fluctuations as resulting from a non equilibrium light flow, characterized by two parameters only, the diffusion coefficient and the mobility, otherwise related by an Einstein relation. A clear asset of this method is its dependence upon two parameters only, which provides a compact yet accurate description of the rich underlying coherent effects. Moreover, the mapping we present between coherent light and out of equilibrium hydrodynamics is easily generalizable to a large class of quantum or classical wave problems.For future perspectives, this connection between coherent effects in mesoscopics and non equilibrium stochastic processes should be of interest in both the mesoscopics and statistical mechanics communities. For the former, the mapping to non equilibrium hydrodynamics provides a new insight to mesoscopic physics as well as useful tools to study quantities so far difficult to access, such as higher orders intensity correlation functions. For the latter, this work should motivate further study of time independent processes inspired from mesoscopics.

A transparência eletromagneticamente induzida (EIT) atraiu bastante atenção no campo da física atômica por suas possíveis aplicações em informação quântica. No entanto, processos transientes em condição de EIT não foram tão largamente estudados. Nesse trabalho, investigamos átomos frios de rubídio sob condição de EIT, num estado transiente. Utilizando espectroscopia de correlação de ruído, que é uma técnica mais sensível que uma espectroscopia de intensidade média, investigamos a resposta atômica assimétrica para uma varredura crescente ou decrescente na frequência do feixe de prova do sistema de Lambda-EIT. A observação dessa assimetria, que não podia ser explicada pelas previsões teóricas baseadas nas equações de Bloch para o átomo de 3-níveis, modelo até então utilizado, nos lançou numa busca pelas possíveis causas desse efeito enigmático. Logo, várias hipóteses foram formuladas, acarretando uma larga exploração experimental, incluindo o ângulo entre os feixes de EIT, dessintonia, potência e direção de incidência do rebombeio. Além disso, espectros no domínio do tempo foram estudados, para entender a evolução temporal do sistema para o estado estacionário. Paralelamente ao experimento, desenvolvemos novos modelos teóricos. Nossa mais recente abordagem teórica modela o sistema como um átomo de 5-níveis, nos quais 3 níveis são referentes ao sistema Lambda e os outros dois são os níveis acoplados pelo rebombeio. Ainda mais, consideramos também as forças óticas no sistema. Esse modelo obteve bom acordo com os dados experimentais, para espectroscopia de intensidade média. / The electromagnetic induced transparency (EIT) has attracted a lot of attention since its applications in quantum information were discovered. However, transient dynamics in this context were not as well explored. Here, we present a study of a cold rubidium ensemble under electromagnetic induced transparency (EIT), during a transient interaction. Using noise correlation spectroscopy, which is a more sensitive technique than a mean intensity spectroscopy, we investigated an asymmetric atomic response to an increasing or decreasing frequency scanning of the probe beams in the Lambda-EIT system. The observation of this asymmetry, which could not be explained by the theoretical predictions based on the Bloch equations for 3-level atom, the previously used model, launched us in a search for possible causes of this enigmatic effect. Straightforward, several hypotheses were formulated, resulting in a wide experimental exploration, including parameters as the angle between the EIT beams, detuning, power and direction of incidence of the repump beam. In addition, spectra in the time domain were studied in order to understand the evolution of the system to the steady-state. Parallel to the experiment, we developed new theoretical models. Our latest theoretical approach models the system as an atom of 5-levels in which 3 levels are related to the Lambda system and the other two levels are coupled by the repump. Moreover, we also consider the optical forces in the system. This model has obtained good agreement with the experimental data, for mean intensity spectroscopy.

A transparência eletromagneticamente induzida (EIT) atraiu bastante atenção no campo da física atômica por suas possíveis aplicações em informação quântica. No entanto, processos transientes em condição de EIT não foram tão largamente estudados. Nesse trabalho, investigamos átomos frios de rubídio sob condição de EIT, num estado transiente. Utilizando espectroscopia de correlação de ruído, que é uma técnica mais sensível que uma espectroscopia de intensidade média, investigamos a resposta atômica assimétrica para uma varredura crescente ou decrescente na frequência do feixe de prova do sistema de Lambda-EIT. A observação dessa assimetria, que não podia ser explicada pelas previsões teóricas baseadas nas equações de Bloch para o átomo de 3-níveis, modelo até então utilizado, nos lançou numa busca pelas possíveis causas desse efeito enigmático. Logo, várias hipóteses foram formuladas, acarretando uma larga exploração experimental, incluindo o ângulo entre os feixes de EIT, dessintonia, potência e direção de incidência do rebombeio. Além disso, espectros no domínio do tempo foram estudados, para entender a evolução temporal do sistema para o estado estacionário. Paralelamente ao experimento, desenvolvemos novos modelos teóricos. Nossa mais recente abordagem teórica modela o sistema como um átomo de 5-níveis, nos quais 3 níveis são referentes ao sistema Lambda e os outros dois são os níveis acoplados pelo rebombeio. Ainda mais, consideramos também as forças óticas no sistema. Esse modelo obteve bom acordo com os dados experimentais, para espectroscopia de intensidade média. / The electromagnetic induced transparency (EIT) has attracted a lot of attention since its applications in quantum information were discovered. However, transient dynamics in this context were not as well explored. Here, we present a study of a cold rubidium ensemble under electromagnetic induced transparency (EIT), during a transient interaction. Using noise correlation spectroscopy, which is a more sensitive technique than a mean intensity spectroscopy, we investigated an asymmetric atomic response to an increasing or decreasing frequency scanning of the probe beams in the Lambda-EIT system. The observation of this asymmetry, which could not be explained by the theoretical predictions based on the Bloch equations for 3-level atom, the previously used model, launched us in a search for possible causes of this enigmatic effect. Straightforward, several hypotheses were formulated, resulting in a wide experimental exploration, including parameters as the angle between the EIT beams, detuning, power and direction of incidence of the repump beam. In addition, spectra in the time domain were studied in order to understand the evolution of the system to the steady-state. Parallel to the experiment, we developed new theoretical models. Our latest theoretical approach models the system as an atom of 5-levels in which 3 levels are related to the Lambda system and the other two levels are coupled by the repump. Moreover, we also consider the optical forces in the system. This model has obtained good agreement with the experimental data, for mean intensity spectroscopy.