NON-LINEAR OPTICS

Author: GONZÁLEZ HERRAEZ MIGUEL.
Year: 2003.
University: POLITÉCNICA DE MADRID [www.upm.es].
Place of defense: E.T.S.I. TELECOMUNICACIÓN.
Place of preparation: INSTITUTO DE FÍSICA APLICADA, CONSEJO SUPERIOR DE INVESTIGACIÓN CIENTIFICAS.

Summary: This thesis describes different methods for measuring longitudinal distribution of chromatic dispersion in optical fibers using non-linear effects. Knowledge of the variations of chromatic dispersion along the fiber will be vital to the successful implementation of systems for the transmission of high-speed (less 40 Gbps) and a great help in the implementation of transmission lines managed dispersing. The first part of the dissertation is a theoretical and experimental study of the various non-linear effects that occur in fiber, particularly the phenomenon of four-wave mixing, which is the basis of the measurement methods proposed in this thesis. Here is the original two methods for measuring distributed chromatic dispersion using four-wave mixing. The first is based on an end-to-end efficiency of the mixing process in a range of wavelengths of pumping. Based on this measure of efficiency spectral mixing we are able to obtain the chromatic dispersion variation that occurs along the fiber through an algorithm original recovery phase. The second method involves an analysis of the efficiency of mixture over fiber using amplification local Brillouin. With this method we showed the best resolutions obtained so far in this kind of measure.

Author: RUIZ MENDEZ CAMILO.
Year: 2004.
University: SALAMANCA [www.usal.es].
Place of defense: EDIFICIO HISTORICO.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: The thesis presented addresses the problems of interaction of an intense laser with atoms and molecules with an emphasis on the mechanisms of correlation between electrons. Over the past decade, advances in technology called laser amplification (CPA Chirped Pulse Amplification) has allowed have laser light sources very intense, above the atomic unit of intensity (I_c = 3.5e14 W / cm ^ 2). When atoms or molecules interact with this light, the same structure of the atom is totally distorted by what a study perturbativo the interaction is no longer possible. In this thesis we address this problem, the ionization of atoms and molecules interacting with an intense laser. The main aim of the thesis is to show the effects of electron correlation between the atom remains very important even though interaction with the laser is so intense. The methodology of the study is the resolution of the ab initio dependent Schroedinger equation of time. The resolution of these numerical equations requires complex numerical techniques and computer massive computation. The most important results of the thesis is as follows: In a one-dimensional model of Helium, which includes accurately interaction between two electrons and the countryside, we have shown that the differences can be observed when comparing two types of Helium atoms. In the case of singlet of Helium, double ionization is more efficient than the hat-trick where the correlation is inhibited. These ideas can be extended to three atoms electrons as Lithium in which there are two channels of ionization. Our model realizes the difference between these two channels and attributed to the effect of the exchange symmetry required by the Pauli exclusion principle.

Author: GIMENO GORMAZ NELIDA.
Year: 2004.
University: ZARAGOZA [www.unizar.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: This thesis describes the preparation and study of different liquid crystals "type banana" with the following results: - The appropriate selection of core angle, the lateral nucleus and chains terminals have yielded new liquid crystals "type banana." Most of the compounds have submitted the mesofase SmCaPa and, in smaller numbers, the sequence of mesofases SmCP-B1 applying electromagnetic fields. The technique makes it possible to obtain light curing situ networks anisótropas orderly macroscopic type SmCP and B1, in the form of actionable films free and stable at room temperature. - For the first time were generated mesofases Type B through hydrogen bond. The complex prepared presented properties mesógenas, dielectric and optics similar to those described for liquid crystals type "banana" covalent. - Has been evaluated activity ONL (GSA) from different materials with order SmCPf, mesofase or networks anisótropas. The non-linear coefficients are measured in the order of d = 1-2pm/VyD = 2-6 pm / V.

Author: Esteban Martín Adolfo.
Year: 2005.
University: VALENCIA [www.uv.es].
Place of defense: Facultat de Física.
Place of preparation: Facultat de Física.

Summary: It has conducted a pilot study of the formation of patterns and structures located in the transverse plane to the propagation of light, using two kinds of oscillators fotorrefractivos (PROs). newspapers and localized structures called domain walls. Moreover, a PRO cavity ring with pumping unidirecional to get a mixture of two non - degenerate waves that displays patterns of vortices. First, it conducted research which verifies, experimentally, the relationship between the number of wave patterns rolls and desintonía. The use of a linear PRO stabilized to degenerate four-wave mixing dimensional (to avoid effects of curvature) has yielded patterns rolls stable unlike experiments on systems not degenerate where there are only so transient. There has been a measure of the free spectral range of active cavity, using a technique based on the extent of two identical numbers wave rolls to vary the length of the cavity. Therefore, it is characterized in terms of desintonía, different structures that are observed in the system, where: rolls, non-periodic structures, homogeneous field and domain walls. Secondly were conducted research on the Transition Ising-Bloch (TIB). They are the first experimental evidence of the existence of Bloch walls and walls of Ising in a cavity optical nonlinear fotorrefractiva. The experimental system used is the PRO linear degenerate four-wave mixing two-dimensional, so the curvature affects the dynamics and nature of the structures. To study the phase and amplitude of the field through the interface, we used a technique interferometric reconstruction. The work reveals the existence of complex structures, which can not be described by equation real Swift-Hohenberg (RSHE). The TIB is studied in a one-dimensional system stabilized and is used to generate an injection of domain walls. Among the most important results include the existence of a TIB which presents a hysteresis cycle used as a parameter to control the desintonía. This can be explained by adding a new term in the non-linear equation complex Ginzburg with broken symmetry phase. Finally presents the detailed characterization of domain walls in the TIB which are covered: edge effects, the method for characterization of the wall by average field complex in the center of the structure, the influence of non-profile of the plane issuing the desintonía and depending on the relationship between speed, intensity and phase gradient of the walls. It also verifies the validity of an experimental parameter quiralidad to characterize the dynamics. Thirdly, investigates the generation and control structures located, introducing what constitutes an optical memory. It uses the PRO linear degenerate four-wave mixing which injects a focused beam in a way that can generate structures localized phase. It shows that controlling the position and phase of the beam injection, it can act on the structures injected. The manipulations presented are writing, erasing and displacement of the structures located. In addition, we studied the conditions for is 8 tabilida 545 d of structures with desintonía and distance of interaction. As an example of optical memory, developed a vector of several structures that can be injected phase switched on / off switch. Finally, it has been verified experimental continuous symmetry breaking phase through the technique of rocking. The system experimentally employee who exhibits invariance phase, is a ring resonator with PRO for not degenerate mixture of two waves, which is referred to rocking injecting a beam modulated in phase with half-wave breaks. The result is the replacement of the vortices by domain walls, which allows demonstrate the breaking of symmetry continuous phase.

Author: GALLASTEGUI MAÑARICUA JOAN ANDER.
Year: 2005.
University: PAÍS VASCO [www.ehu.es].
Place of defense: FACULTAD DE CIENCIA Y TECNOLOGÍA.
Place of preparation: FACULTAD DE CIENCIA Y TECNOLOGÍA.

Summary: The present work has been carried out a study of different optical properties both linear and non-linear electroópticas, and a set of structural materials belonging to a new type of liquid crystals of the type known as' banana '. From the point of view molecular these compounds show a combada from which it derives its name. It is this peculiar form which gives them interesting physical properties. Por una parte presentan mesofases cuyas estructuras son muy diferentes de las típicas de cristales líquidos convencionales usualmente calamíticos (cuyas moléculas son alargadas). On the other hand, they have nonlinear optical responses of a very high efficiency, which, in principle, is a big attraction from the standpoint of their potential technological applications. In this work has been done caracterizaicón full tensor that describes the efficiency of second harmonic generation in a large family compound, and as a result more remarkable it is worth noting that in all cases such efficiency is an order of magnitude higher than the conventional liquid crystals, and in some cases up to two orders higher. It also carried out in some cases an interest an exhaustive study of various properties electroópticas, which detected for the first time transitions induced by the electric field between columnar phases (two-dimensional) and esmécticas (one-dimensional). The structural properties of the materials in which it was observed this phenomenon were also analyzed by x-ray diffraction low angle. Moreover were obtained fotopolímeros based on such materials. These have the advantage of presenting polar order, and thus allow the generation of second harmonic, without applying electric fields. Also present an improved performance from the point of view of potential technological applications. Así mismo, el proceso de fotopolimerización permitió obtener películas debidamente orientadas en ausencia de campo aplicado ya temperatura ambiente, en los que fue posible llevar a cabo un estudio estructural imposible de realizar en la mesofase sin polimerizar debido a la absorción de rayos x por parte de the cell.

Author: PAZ ALONSO MARÍA JESÚS.
Year: 2005.
University: VIGO [www.uvigo.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: The overall purpose of this dissertation is to study, using numerical simulations, the beam propagation of laser light in the so-called optical cúbico-químicos (CQ). These materials are characterized by having a refractive index that depends on the strength of the incident light beam, so that is autoenfocante for low intensities and autodesenfocante for high intensities. In such media acquires some light physical properties similar to those of the fluid, such as the existence of stable vortices and surface tension. This process can be interpreted as a transition phase of a gas of photons to a 'liquid light'. First has been studied, so theoretically, using a system with four levels atomic electromagnetically induced transparency (EIT) to reach a situation with sensitivities of the third and fifth order giant and opposite sign. An appropriate choice of parameters used to obtain two-dimensional condensates light stable. Our theoretical results could be the basis for real experiments in nonlinear optics with lasers continuing mW. For the determination of non-linear refractive indices, it has been considered the Z-scan technique. It has developed a simple theory based on the method of moments, which allows you to adjust the experimental data Z scan. There have been stationary states of the equation nonlinear Schrà ¶ dinger CQ, for different beam powers, and have been formulated ideals experiments to study their dynamics. The physical properties of the resulting state, as surface tension, are similar to those of normal fluids. After a comparison was made between states stationary environment CQ and those obtained for the system of four levels with atomic EIT, giving very similar results. Subsequently states have been calculated in ways CQ vortex type, for different values of angular momentum and different potentials. Through an analysis of stability, we have shown that these distributions are stable when light is propagated, probably for unlimited values of angular momentum, as long as the beam that contains is sufficiently wide. These stationary states are very similar to those obtained for the middle with EIT. To demonstrate the stability of states types vortex has been simulated total reflection light beams containing vortices at the border of a material non-linear CQ and air, couple different angles of incidence. The surface tension prevents beam filamentation for a certain range of angles of reflection all, even in the case where the và ¶ rtice be divided causing vortices lower angular momentum. Finally, it has been shown that it is possible to generate vortices networks stable in light condensates. This is sufficient to propagate several concentric beam containing vortices with different angular momentum in a material CQ. The motion of the vortices in the network is very similar to that of the vortices in superfluidos, described by the law of Kelvin. The number of network components is determined by the difference vorticity of the initial beams, and the net angular momentum in the same match, in all cases, with the initial external beam.