In this dissertation, we first derive exact reconstuction algorithms for thermoacoustic tomography (TAT) and broadband diffraction tomography (a linearized inverse scattering problem) using derived time-reversal formulas. Then we focus on some important practical problems of TAT including the limited-view problem, the effects of acoustic heterogeneity, and fast reconstruction algorithms. In Chapter II, we propose time-reversal methods and apply them to tomography with diffrating sources. We first develop time-domain methods to time-reverse a transient scalar wave using only the field measured on an arbitrary closed surface enclosing the initial sources. Under certain conditions, a time-reversed field can be obtained with the delay-and-sum algorithm (backprojection to spheres) used in synthetic aperture imaging.Consequently, the physicalmeaningandthe validconditions of this widely used algorithm are revealed quantitatively for the first time from basic physics. Then exact reconstruction for TAT and broadband diffraction tomography is proposed by time-reversing the measured field back to the time when each source or secondary source is excited. The theoretical conclusions are supported by a numerical simulation ofthree-dimensional diffraction tomography.The extension ofour time-reversal methods to the case using Green function in a heterogeneous medium is also discussed. In Chapter III, the limited-view problem is studied for TAT. We define a "detection region," within which all points have sufficient detection views. It is explained analytically and shown numerically that the boundaries of any object inside this region can be recovered stably.Otherwise some sharp details become blurred.One can identify in advance the parts of the boundaries that will be affected if the detection view is insufficient. Computations are conducted for both numerically simulated and experimental data. The reconstructions confirm our theoretical predictions. In Chapter IV, the effects of wavefront distortions induced by acoustic heterogeneities in breast TAT are studied. Amplitude distortions are shown to be insignificant for different scales of acoustic heterogeneities. After that we consider the effects of phase distortions (errors in time-of-flight) in our numerical studies. The numerical results on the spreads of point sources and boundaries caused by the phase distortions are in good agreement with the proposed formula. We also demonstrate that the blurring of images can be compensated for by using the distribution of acoustic velocityin the tissues in the reconstructions. In Chapter V, we discuss exact and fast Fourier-domain reconstruction algorithms for TAT in planar and circular configurations.

In this dissertation, we first derive exact reconstuction algorithms for thermoacoustic tomography (TAT) and broadband diffraction tomography (a linearized inverse scattering problem) using derived time-reversal formulas. Then we focus on some important practical problems of TAT including the limited-view problem, the effects of acoustic heterogeneity, and fast reconstruction algorithms. In Chapter II, we propose time-reversal methods and apply them to tomography with diffrating sources. We first develop time-domain methods to time-reverse a transient scalar wave using only the field measured on an arbitrary closed surface enclosing the initial sources. Under certain conditions, a time-reversed field can be obtained with the delay-and-sum algorithm (backprojection to spheres) used in synthetic aperture imaging.Consequently, the physicalmeaningandthe validconditions of this widely used algorithm are revealed quantitatively for the first time from basic physics. Then exact reconstruction for TAT and broadband diffraction tomography is proposed by time-reversing the measured field back to the time when each source or secondary source is excited. The theoretical conclusions are supported by a numerical simulation ofthree-dimensional diffraction tomography.The extension ofour time-reversal methods to the case using Green function in a heterogeneous medium is also discussed. In Chapter III, the limited-view problem is studied for TAT. We define a "detection region," within which all points have sufficient detection views. It is explained analytically and shown numerically that the boundaries of any object inside this region can be recovered stably.Otherwise some sharp details become blurred.One can identify in advance the parts of the boundaries that will be affected if the detection view is insufficient. Computations are conducted for both numerically simulated and experimental data. The reconstructions confirm our theoretical predictions. In Chapter IV, the effects of wavefront distortions induced by acoustic heterogeneities in breast TAT are studied. Amplitude distortions are shown to be insignificant for different scales of acoustic heterogeneities. After that we consider the effects of phase distortions (errors in time-of-flight) in our numerical studies. The numerical results on the spreads of point sources and boundaries caused by the phase distortions are in good agreement with the proposed formula. We also demonstrate that the blurring of images can be compensated for by using the distribution of acoustic velocityin the tissues in the reconstructions. In Chapter V, we discuss exact and fast Fourier-domain reconstruction algorithms for TAT in planar and circular configurations.

Over the years, non-spreading or non-diffracting wave configurations have been systematically investigated in optics. Perhaps the best known example of a diffraction-free optical wave is the so-called Bessel beam, first suggested and observed by Durnin et al. This work sparked considerable theoretical and experimental activity and paved the way toward the discovery of other interesting non-diffracting solutions. In 1979 Berry and Balazs made an important observation within the context of quantum mechanics: they theoretically demonstrated that the Schrodinger equation describing a free particle can exhibit a non-spreading Airy wavepacket solution. This work remained largely unnoticed in the literature-partly because such wavepackets cannot be readily synthesized in quantum mechanics. In this dissertation we investigate both theoretically and experimentally the acceleration dynamics of non-spreading optical Airy beams in both one- and two-dimensional configurations. We show that this class of finite energy waves can retain their intensity features over several diffraction lengths. The possibility of other physical realizations involving spatio-temporal Airy wavepackets is also considered. As demonstrated in our experiments, these Airy beams can exhibit unusual features such as the ability to remain quasi-diffraction-free over long distances while their intensity features tend to freely accelerate during propagation. We have demonstrated experimentally that optical Airy beams propagating in free space can perform ballistic dynamics akin to those of projectiles moving under the action of gravity. The parabolic trajectories of these beams as well as the motion of their center of gravity were observed in good agreement with theory. Another remarkable property of optical Airy beams is their resilience in amplitude and phase perturbations. We show that this class of waves tends to reform during propagation in spite of the severity of the imposed perturbations. In all occasions the reconstruction of these beams is interpreted through their internal transverse power flow. The robustness of these optical beams in scattering and turbulent environments was also studied. The experimental observation of self-trapped Airy beams in unbiased nonlinear photorefractive media is also reported. This new class of non-local self-localized beams owes its existence to carrier diffusion effects as opposed to self-focusing. These finite energy Airy states exhibit a highly asymmetric intensity profile that is determined by the inherent properties of the nonlinear crystal. In addition, these wavepackets self-bend during propagation at an acceleration rate that is independent of the thermal energy associated with two-wave mixing diffusion photorefractive nonlinearity.

This thesis presents a study into structural colours that exist in natural samples, the principle aim of which is to produce experimental methods by which these colours may be examined and evaluated. In order to achieve this, previously observed structures are described, electromagnetic theory is summarised and a series of samples are examined constituting examples of the structures present in nature. The first sample discussed is the multilayer in the epicuticle of the buprestid beetle, C. raja. In order to evaluate the refractive indices of the layers contained within this structure, existing optical techniques are used to establish absolute reflection spectra for a number of angles of incidence in both linear polarisations. The approximate design for the structure is obtained by electron microscopy and modelled using Fresnel's equations. This model is then refined by a recursive least squares fitting routine to obtain the refractive indices. The second sample is the diffuse white scattering structure in the scales of two white beetles, Lepidiota stigma and Cyphochilus spp. The reflection from these scales is measured and found to be brilliantly white due to the irregular internal structure of the scales. Comparison of the Fast Fourier Transforms of TEM images of the internal structure with the diffraction pattern obtained from monochromatic laser light diffracting through a single scale demonstrate a link between this structure and photonic effects. The third sample type are found in the scales of the large true weevils, Eupholus schoenherri pettiti and E. magnificus. These scales are shown to have a domained structure in which the domains were oriented differently to each other. Single domains are shown to exhibit different colours at different orientation. The final sample is the highly regular 2-dimensional diffraction grating observed in a marine diatom, Coscinodiscus wailesii. Diffraction is demonstrated by measuring the in-plane diffraction from a single frustule for both monochromatic laser light and white light, showing an enhanced transmission for red wavelengths. Subsequent imaging of the transmitted diffraction pattern allows for the calculation of the transmitted power in each diffracted order.

The performance of various designs of outdoor noise barrier has been investigated using numerical modelling and full scale experiments. The numerical modelling has been performed using a two-dimensional boundary element method. The model has been extended to allow the efficient simulation of barrier arrangements on ground having two distinct impedance values and cross-sections incorporating cuttings. It has been reported previously that the performance of a plane screen can be enhanced by adding a device to the top of the barrier to induce destructive interference. Full scale modelling and boundary element simulations have been performed on one such commercially available device. It has been shown that, taking the height increase into account, the major contribution to the improved performance is the presence of two diffracting edges rather than any interference effects generated. It is known that the performance of a single barrier is degraded following the introduction of a barrier on the opposite side of a source. Boundary element simulations of such parallel arrangements have been performed. Modifications have been proposed to reduce the over-estimation of multiple reflections within the model, together with a method for converting predictions to the equivalent point source values. Sound absorptive, tilted and median barriers have been shown to be effective in reducing the degradation. A multiple-edge barrier configuration is known to offer improved screening performance over a plane screen. Reported in-situ measurements have suggested the behaviour to be influenced by site geometry. Boundary element calculations have been performed to identify a more efficient variant of the device. The results suggest the addition of an inclined base panel to be most effective. The boundary element model has been used to investigate the effect of shape and surface treatment upon railway noise barriers. The model has been adapted to allow the use of dipole sources characteristic of railway noise. The cross-section of the rolling stock has been shown to affect the performance of rigid barriers. If the upper edges are coincident, the results suggest that simple absorptive barriers provide better screening than tilted designs. The addition of multiple edges further enhances performance.

The scattered field from an object, when illuminated with ultrasound, is useful in the reconstruction of it's cross section - a problem broadly classified as 'tomography'. In many situations of medical imaging, we will be interested in getting to know the location and the extent of growth of the inhomogeneity. The Maximum Likelihood (ML) estimation of the location and the shape parameters (of scale and orientation angle), has been done along with the corresponding CR bounds, for the case of weakly scattering objects, where the Fourier Diffraction Theorem(FDT) holds. It has been found that the a-priori information of a reference object function helps in drastic reduction of the number of receivers and illuminations required. For a polygonal object, the shape is specified, when the corner locations are known. We have formulated the problem as, estimation of the frequencies of sum of undamped sinusoids. The result is a substantial reduction in the number of illuminations and receivers required. For acoustically soft and rigid polygons, where the FDT does not hold, the necessary theory is developed to show the dependence of the scattered field on the corner location, using an On Surface Radiation Condition(OSRC). The corner locations are estimated along similar lines, to the one adopted for the weakly scattering objects.

This thesis describes an innovative method for topographic measurement of diffuse surfaces. Tested surface is measured indirectly using nanoparticles distributed across the studied area. An image of every particle is captured by CCD camera as a double helix point spread function whose angular rotation corresponds to local surface height. Used point spread function is the result of an interference of non-diffracting vortex beams that are formed by a spiral phase mask from light originating from a nanoparticle. Diploma thesis presents an overview of current techniques for surface topography measurement. Next, working principle of proposed method is described and its experimental application is discussed. An influence of signal-to-noise ratio and image sampling on reconstruction precision is studied using numerical simulations and, as a result, optimal experimental parameters are proposed. Practical potential of the method is demonstrated by 3D reconstruction of planar and spherical surfaces in the depth range of up to 9 times the depth of focus of used microscope objective.

Orientadores: Michel Zamboni Rached, Guillermo Gerardo Cabrera Oyarzún / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-09-01T02:33:12Z (GMT). No. of bitstreams: 1 Pachon_EdwinGermanPinilla_D.pdf: 4993091 bytes, checksum: 788c9fb47dfe7b9fea6cc0935ad94d54 (MD5) Previous issue date: 2016 / Resumo: Nesta tese, propõe-se um novo método para realizar guiamento de átomos neutros resfriados. Este método envolve o uso da pressão de radiação por ressonância para efetuar o guiamento dos átomos através de um campo óptico (feixe) oco. Particularmente, usa-se a força de dipolo óptico e um tipo específico de campo óptico não difrativo, chamado de "Frozen Wave" (FW), na versão tradicional e estendida, para estudar o guiamento atômico. Os campos ópticos FW¿s, que são uma solução exata da equação de onda, surgem como uma resposta aos problemas relacionados com a difração e com a impossibilidade de fazer qualquer tipo de modelamento (ou localização) longitudinal e transversal de intensidade, dos campos ópticos tradicionais usados no guiamento de átomos, como por exemplo, nos campos Laguerre-Gauss e Bessel. Assim, planejam-se algumas soluções mediante os métodos tradicional e estendido que permitem criar estruturas de luz (localizadas) resistentes à difração e nas quais o padrão de intensidade longitudinal e transversal (restringido) pode ser modelado a priori. De acordo com isso, o estudo teórico do método tradicional e da generalização das FW¿s foi realizado junto com sua comprovação experimental e foram calculados os respectivos potenciais de dipolo óptico junto com a profundidade de penetração dos átomos na barreira de potencial para cada campo óptico. Nos resultados conseguiu-se modelar algumas estruturas de luz (tanto no método tradicional como no estendido) tais como um cilindro, três cilindros concatenados, um tipo de cilindro com tampa e um funil óptico, entre outras; e mostrou-se as vantagens do uso deste tipo de estruturas de luz quando comparadas com os campos ópticos tradicionais para o guiamento atômico. Finalmente, concluiu-se que usar este tipo de campos não difrativos elimina as restrições dos campos tradicionais e é possível fazer o guiamento de átomos neutros resfriados com estes tipos de estruturas de luz. O método estendido dá uma generalização que permite pensar estes tipos de estruturas de luz para aplicações mais globais nas diferentes áreas da óptica e fotônica / Abstract: This thesis proposes a new method to perform cold neutral atom guiding. This method involves the use of resonance radiation pressure to make the atom guiding along a hollow (beam) optical field. Particularly, it uses the optical dipole force and a specific type of non-diffracting optical field, called "Frozen Wave" (FW), in these traditional and extended versions, to study the atom guiding. The FW¿s optical fields, which are an exact solution of the wave equation, appear as an answer to the problems related to the high diffraction and impossibility of any type of longitudinal and transverse intensity modeling (or location) of traditional optical fields used in atom guiding, for example the Laguerre-Gaussian and Bessel optical fields. Thus, some solutions were planned by the traditional and extended methods, which allow to create localized light structures resistant to diffraction and model a priori longitudinal and transverse (restricted) intensity pattern. Accordingly, the theoretical study of the traditional method and his generalization were carried out with their experimental evidence. Also, his respective optical dipole potential was calculated with the atom penetration depth in the potential barrier for each optical field. In the results was possible to model some light structures (both in the traditional and extended method) such as a cylinder, three concatenated cylinders, one cylinder with a lid and an optical funnel, among others; and it is showed the advantages of using this type of light structures when it is compared with the conventional optical fields for the atom guiding. Finally, it is concluded that use this type of non-diffracting fields eliminates the restrictions of the traditional fields and it is possible the cold neutral atoms guiding with this type of light structures. The FW¿s extended method gives a generalization and it permits to suggest this type of light structures for more complete applications in different areas of optics and photonics / Doutorado / Física / Doutor em Ciências / 141977/2013-2 / CNPQ

Continuing advances in laser and photonic technology has seen the development of lasers with increasing power and increasingly short pulsewidths, which have become available over an increasing range of wavelengths. As the availability of laser sources grow, so do their applications. To make better use of this improving technology, understanding and controlling laser propagation in free space is critical, as is understanding the interaction between laser light and matter. The need to better control the light obtained from increasingly advanced laser sources leads to the emergence of beam engineering, the systematic understanding and control of light through refractive media and free space. Beam engineering enables control over the beam shape, energy and spectral composition during propagation, which can be achieved through a variety of means. In this dissertation, several methods of beam engineering are investigated. These methods enable improved control over the shape and propagation of laser light. Laser-matter interaction is also investigated, as it provides both a means to control the propagation of pulsed laser light through the atmosphere, and provides a means to generation remote sources of radiation.