Assignatura Òptica Geomètrica

Assignatura Òptica Geomètrica

Assignatura Òptica Geomètrica

El objetivo de este trabajo es validar una cámara de fondo de ojo basada
en sistemas de imagen hiperespectral, con la que se pueden obtener 15 imágenes
espectrales a diferentes longitudes de onda del espectro visible (VIS) y del infrarrojo
cercano (NIR) (400nm a 1300nm). Se han obtenido las imágenes de 38 pacientes de
edades entre 30 y 90 años y, posteriormente, se ha realizado un análisis
espectroscópico. Para cada imagen procesada del fondo de ojo se han extraído los
valores de reflectancia de cada estructura en función de la longitud de onda y de la
edad del paciente. De esta manera podemos estudiar las propiedades espectrales de las
sustancias que se encuentran en el fondo de ojo para la luz VIS y NIR.
Los resultados muestran que las longitudes de onda más cortas (<500nm) se reflejan
más superficialmente, lo cual nos permite obtener información de estructuras como el
disco óptico, las fibras nerviosas y la fóvea. Las longitudes de onda intermedias
(500nm-700nm) permiten observar con detalle los vasos sanguíneos de la retina, y
diferenciar las arterias de las venas. Finalmente, el uso de luz NIR permite observar
estructuras más profundas como la coroides y sus vasos, las cuales no podemos
observar con un retinógrafo convencional, debido a la alta absorbancia de la melanina
a la luz VIS. En conclusión, usar una cámara hiperespectral con longitudes de onda por
encima del VIS permite visualizar mejor algunas estructuras concretas y capas más
profundas así como obtener información espectroscópica de las mismas.

Forward stimulated Brillouin scattering (FSBS) in optical fibers is a
phenomenon that has been studied since mid-80s. It is produced when two
copropagating optical waves are scattered by transverse acoustic waves, generating
frequency shifts up to 1 GHz. These acoustic resonances can be excited by electrostriction
when an intense optical pulse propagates inside the fiber. Perturbations in the effective
index of the guided mode are generated through the photo-elastic effect, which typically
are detected by direct analysis of the scattered optical wave. Here we propose an
alternative observation method through the use of a long-period grating (LPG). LPGs
are fiber devices that couples light from the fundamental optical core mode to copropagating cladding modes. Their transmission spectra present several attenuation
notches corresponding to the excitation of different cladding modes that satisfy the
resonance condition. These resonance condition depend on the effective index of the
coupled core and cladding modes and is therefore sensitive to perturbations. The change
in transmission of the LPG becomes then an efficient method of interrogation for FSBS
in optical fibers. The linewidth of resonances was found to be much shorter than in
previous reports in which long fiber lengths are typically required

A methodology to retrieve the dielectric function of a nanocomposite from infrared spectroscopy is presented. The use of effective medium theories allows treating the optical response of a multi-phase composite as that of a single phase with an effective response that is a complex function of the components and their spatial arrangement. This methodology has been tested in a case study involving cerium oxide nanoparticles, whose vibrational properties are known to change significantly upon particle size reduction. Accurate values of its dielectric function in the infrared have been retrieved and used to analyse this phenomenon. The main goal of this study is to develop a systematic methodology for the study of the vibrational properties of nanomaterials. It is also intended that the development of effective medium models will be useful for designing new composite nanomaterials with improved optical properties (e.g., solar absorbers).

Red blood cells (RBCs) alterations can cause very severe blood diseases. In thalassemia, the production of hemoglobin polypeptide chains is unbalanced. This causes no symptoms or small blood count alterations in patients with less important genetic mutations, or severe anemia and high morbi-mortality in the most severe cases. Traditional techniques do not perfectly discriminate among different thalassemia degrees and most patients need to undergo genetic studies. Authors have tried alternatives to analyze RBCs, collecting their emission and absorption spectral traits with spectrometers and spectrofluorometers. Multispectral imaging with confocal microscopy allows capturing both tridimensional and spectral information. In this study we are using confocal spectral imaging to analyze RBCs from patients with different degrees of alpha-thalassemia and iron deficiencies. The instrument, a Leica TCS SP8 confocal microscope has high sensitivity hybrid cameras, a diode laser and a white laser combined with an acoustic-optic tunable filter. RBCs exhibited autofluorescence when excited at 405 nm. The mean emission intensities at 502 nm, 628 nm and 649 nm allowed us to discriminate between different etiologies.

En la industria del color es muy importante conocer la gama de colores de un dispositivo. Mediante la comparación de gamas podemos evaluar el efecto que tiene el uso de distintas tintas, papeles, fuentes de iluminación o dispositivos de impresión en el color obtenido. Existen diversos programas que realizan esta comparación, pero tienen inconvenientes. Por ello hemos desarrollado y validado un software para comparar gamas de color generadas por impresoras. El software representa las gamas simultáneamente en el espacio 3D CIELAB, además de calcular su volumen. Para validar nuestro software hemos realizado un doble análisis. Por un lado, hemos comparado los resultados obtenidos a partir de nuestro software y los obtenidos con otros métodos de comparación, como la representación en diferentes espacios de color. Por otro lado, hemos usado el programa ICC3D para comparar las representaciones de las gamas con las de nuestro programa, además del volumen. Con ambos programas las conclusiones fueron similares, aunque nuestro software presenta algunas ventajas, permitiendo distinguir diferencias entre las gamas que mediante otros métodos no se discriminaron. Este nuevo software va a permitir el estudio de la influencia de distintos factores en la reproducción del color, permitiendo conocer las condiciones para conseguir la mejor calidad posible

Imaging through nebulous media encountered in nature – like fog – is one
of the up-to-date research questions in the field of navigation. Among different
approaches to solve this problem, the use of polarimetric imaging has been proposed.
The aim of this research is to present a polarized light propagation model based on
Monte-Carlo simulations and Mie Theory for its use as a tool to study the feasibility and
characteristics of polarized light detection techniques in these kinds of media. Studying
and obtaining the backscattering Mueller matrix for a turbid environment allows to
completely characterize the backscattering characteristics of the media. Thus, it may be
used to select the combination of polarization components more useful for each
situation. On the other hand, it has been seen that when light first interact with fog,
generated backscatter directly blinds the sensor of the imaging device and hides
reflected signals of objects being imaged. Using a time-resolved variant of the model, it
has been possible to characterize the shape and the influence of the temporal response
of a backscattered light pulse, concluding that, apart from the greater light extinction in
a more scattering medium, media-backscattering and reflected-object signals are
independent

Complete characterization of biological samples is of potential interest in different industrial and research areas, as for instance, in biomedical applications, for the recognition of organic structures or for the early detection of some diseases. During the last decades, polarimetric methods are experiencing an increase of attention in the study of biomedical tissues, and they are nowadays used in such framework to provide qualitative (polarimetric imaging) and quantitative (data processing) information for the studied samples. Polarimetric methods are based on the analysis of polarization modifications produced by lightmatter interactions which can be triggered by a number of complex internal processes but can be roughly understood as the result of the combination of three pure polarimetric features of the sample: its diattenuation, retardance and depolarization. To describe the depolarization sample behavior, we use the Indices of Polarimetric Purity (IPP): related with the randomness of the scattering processes, IPPs provide more information of depolarizing systems than the widely used depolarization index, 𝑃∆, which further synthetizes the depolarization content of samples. As a result, IPPs allow the revelation of some structures from tissue samples (animal and vegetal) hidden in regular intensity images of even in the 𝑃∆ channel, leading to better tissue classification results.

The study of tissue optics is relevant for developing innovative non-invasive diagnostic and therapeutic techniques, and optical phantoms that simulate light propagation processes through soft biological tissue are required to evaluate the performance and calibrate different medical imaging modalities. Liquid lipid based low-cost phantoms were prepared, with cow’s milk as scattering material, Red India ink as the absorbing material and demineralized water as the matrix material since it provides a soft medium biologically compatible with the addition of organic molecules. Two experiments were carried out for characterization of this tissue model. First, collimated and diffuse transmittance and reflectance spectra were measured using phantoms with milk of different fat content. From the data, dependence between: total extinction coefficient, Kubelka Munk’s ratio, absorption and scattering coefficients on the wavelength were estimated. Second, using collimated transmittance measurements the effect of the phantom components was observed. The absorption peak, increases as ink was added to phantoms; and when lipid concentration was varied, by fixed ink, the scattering growths. The extinction coefficient’s dependence on the wavelength was determined, and fluorescence was observed. Results confirm the possibility of spectroscopic identification of milk kinds, as well as the feasibility of low-cost controllable phantom for preliminary biophotonic studies.

Electron-electron correlation is at the origin of complexity in multi-electron systems. Since the total response of a complex system is not the sum of its independent constituents, the many-electron problem remains a computational challenge even though understanding correlation mechanisms is essential for a full control of the electric and magnetic properties of matter. In this work, we disentangle the fingerprints of correlated electron dynamics in the strong laser-atom interaction of the simplest multi-electron system. The two electrons of the helium atom interacting with an intense electromagnetic field represent an extraordinary scenario to explore correlations from a fundamental view, since we can perform a numerical integration of the time-dependent Schrödinger equation. Our theoretical results predict a correlation mechanism of back-reaction showing a distinctive signature in high-order harmonic generation. An extension of the high-harmonic spectra towards higher frequencies encodes the information of back-reaction. This finding demonstrates that correlation phenomena can be tracked with high-harmonic spectroscopy, and opens the possibility to experimentally probe complex systems.