Programmable optics for ultrashort pulse management: devices and applications

The contribution of the present report to the field of ultrashort optics has several aspects: from the development of new optical devices for ultrashort pulse management, to the application of those devices for triggering laser-matter interaction processes. In this sense, the key point of this Thesis is the use of reconfigurable phase-only SLMs based on LCOS technology for spatial and temporal shaping of femtosecond pulses. The management of femtosecond pulses demands specific strategies to obtain the desired output response while preventing undesirable distortions. Our results show that programmable diffractive optics encoded in SLMs is a powerful tool for ultrashort (~30 fs) beam management. The reconfigurable nature of SLMs allows wavefront control of an input pulsed beam at a micro scale level. In this way, we have developed devices for transferring amplitude and/or phase maps onto the spatial and temporal profile of an ultrashort pulse. Moreover, our proposals result in very compact optical devices, allowing easy-to-align setups especially suitable for non-expert users. We believe that this fact may promote the use of ultrafast technology in many different scientific fields that demands user-friendly devices for ultrashort pulse control

Surgical Guidance for Removal of Cholesteatoma Using a Multispectral 3D-Endoscope

We develop a stereo-multispectral endoscopic prototype in which a filter-wheel is used for surgical guidance to remove cholesteatoma tissue in the middle ear. Cholesteatoma is a destructive proliferating tissue. The only treatment for this disease is surgery. Removal is a very demanding task, even for experienced surgeons. It is very difficult to distinguish between bone and cholesteatoma. In addition, it can even reoccur if not all tissue particles of the cholesteatoma are removed, which leads to undesirable follow-up operations. Therefore, we propose an image-based method that combines multispectral tissue classification and 3D reconstruction to identify all parts of the removed tissue and determine their metric dimensions intraoperatively. The designed multispectral filter-wheel 3D-endoscope prototype can switch between narrow-band spectral and broad-band white illumination, which is technically evaluated in terms of optical system properties. Further, it is tested and evaluated on three patients. The wavelengths 400 nm and 420 nm are identified as most suitable for the differentiation task. The stereoscopic image acquisition allows accurate 3D surface reconstruction of the enhanced image information. The first results are promising, as the cholesteatoma can be easily highlighted, correctly identified, and visualized as a true-to-scale 3D model showing the patient-specific anatomy.Peer Reviewe

Optogenetic Interrogation and Manipulation of Vascular Blood Flow in Cortex

Understanding blood flow regulatory mechanisms that correlate the regional blood flow with the level of local neuronal activity in brain is an ongoing research. Discerning different aspects of this coupling is of substantial importance in interpretation of functional imaging results, such as functional magnetic resonance imaging (fMRI), that rely on hemodynamic recordings to detect and image brain neuronal activity. Moreover, this understanding can provide insight into blood flow disorders under different pathophysiological conditions and possible treatments for such disorders. The blood regulatory mechanisms can be studied at two different; however, complementary levels: at the cellular level or at the vascular level. To fully understand the regulatory mechanisms in brain, it is essential to discern details of the coupling mechanism in each level. While, the cellular pathways of the coupling mechanism has been studied extensively in the past few decades, our understanding of the vascular response to brain activity is fairly basic. The main objective of this dissertation is to develop proper methods and instrumentation to interrogate regional cortical vasodynamics in response to local brain stimulation. For this purpose we offer the design of a custom-made OCT scanner and the necessary lens mechanisms to integrate the OCT system, fluorescence imaging, and optogenetic stimulation technologies in a single system. The design uses off-the-shelf components for a cost-effective design. The modular design of the device allows scientists to modify it in accordance with their research needs. With this multi-modal system we are able to monitor blood flow, blood velocity, and lumen diameter of pial vessels, simultaneously. Additionally, the system design provides the possibility of generating arbitrary spatial stimulation light pattern on brain. These abilities enables researchers to capture more diverse datasets and, eventually, obtain a more comprehensive picture of the vasodynamics in the brain. Along with the device we also proposed new biological experiments that are tailored to investigate the spatio-temporal properties of the vascular response to optical neurostimulation of the excitatory neurons. We demonstrate the ability of the proposed methods to investigate the effect of length and amplitude of stimulation on the temporal pattern of response in the blood flow, blood velocity, and diameter of the pial vessels. Moreover, we offer systemic approaches to investigate the spatial characteristics of the response in a vascular network. In these methods we apply arbitrary spatial patterns of optical stimulation to the cortex of transgenic mice and monitor the attributes of surrounding vessels. With this flexibility we were able to image the brain region that is influenced by a pial artery. After characterizing the spatio-temporal properties of the vascular blood flow response to optical neuro-modulation, we demonstrate the design and application of an optogenetic-based closed-loop controller mechanism in the brain. This controller, uses a proportional–integral–derivative (PID) compensator to engineer temporal optogenetic stimulation light pulses and maintain the flow of blood at various user defined levels in a set of selected arteries. Upon tuning the gain values of the PID controller we obtained a near to critically-damped response in the blood flow of selected arterial vessels

Aberraciones cromáticas, monocromáticas y diseños multifocales: interacción e impacto en la visión

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Óptica y Optometría, leída el 21/01/2021An important part of the information that we receive from the world is through the sense of vision: the eye projects images on the retina, which transforms them into nerve impulses that reach the neuronal cortex, where these impulses are interpreted. However, the images projected onto the retina are not perfect, as they are affected by diffraction, scattering, and aberrations, which degrade contrast and decrease the resolution limit of the eye. To understand the effect of aberrations on vision, it is necessary to develop technologies and experiments that allow objectively and subjectively assess their interaction. In this sense, Adaptive Optics (AO) has played an important role in increasing our knowledge about the neural processes of vision, since AO can be used to measure, correct and induce aberrations. Understanding what role aberrations play and what their impact is on vision will help to develop better correction designs for the eye. The manipulation of the wavefront using AO also allows to induce a certain visual correction, so it can be used as a basis for visual simulators. As AO allows studying a new lens design or comparing across different lens designs even before they are manufactured, this is an excellent tool to test and improve optical corrections before they are implanted in the eye of a patient. Different technologies including deformable mirrors (DM), spatial light modulators (SLM), or temporal multiplexing by an optotunable lens (SimVis), are currently being validated and launched into the clinical practice. In this thesis, AO technologies have been implemented and used both to study the effect of aberrations and to cross-validate different simulator modalities...Una importante parte de la información que recibimos del mundo lo hacemos a través del sentido de la visión: el ojo proyecta las imágenes en la retina, la cual las transforma en impulsos nerviosos que llegan hasta el córtex neuronal, donde se interpretan estos impulsos. Sin embargo, las imágenes proyectadas en la retina no son perfectas, ya que están afectadas por la difracción, la dispersión y las aberraciones, que degradan el contraste y reducen el límite de resolución del ojo. Para entender el efecto de las aberraciones en la visión es necesario desarrollar tecnologías y experimentos que permitan valorar objetiva y subjetivamente su interacción. En este sentido, la Óptica Adaptativa (AO) ha jugado un papel importante en el incremento de nuestro conocimiento acerca de los procesos neuronales de la visión, ya que la AO se puede utilizar para medir, corregir e inducir aberraciones. Comprender qué papel juegan las aberraciones y cuál es su impacto en la visión, ayudará a desarrollar mejores diseños de corrección para el ojo, sin embargo, aún no se entiendo completamente. La manipulación del frente de onda mediante AO permite, además, inducir una cierta corrección visual, por lo que se puede utilizar como base de simuladores visuales. Estudiar un nuevo diseño o comparar varios diseños entre ellos antes incluso de que sean fabricados, plantea la AO como una excelente herramienta para probar y mejorar una corrección antes de que sea implantada. Para ello, diferentes tecnologías como los espejos deformables, los Moduladores Espaciales de Luz (SLM), la multiplexación temporal inducida por una lente optoajustable (SimVis), están siendo en la actualidad validados y lanzados a la práctica clínica. En esta tesis se ha utilizado la AO tanto para estudiar el efecto de las aberraciones como comparar diferentes simuladores visuales...Fac. de Óptica y OptometríaTRUEunpu

Modeling of magnetic optic for the short pulse mode operation of Energy Recovery Linac based light sources

Das Forschungsfeld der Synchrotronstrahlungsquellen hat sich in den letzen Jahren entscheidend weiterentwickelt. Alle Zukunftsideen, unabhängig von ihrer Komplexität, haben dennoch eines gemeinsam: die Erzeugung kurzer Pulse. Die Naturwissenschaften haben die Spitzenbrillanz, die mit Hilfe kürzester Pulse produziert werden kann, als neues Schlüsselwerkzeug entdeckt. Die Nutzergemeinschaft verlangt nicht mehr nur ein statisches Bild, sondern vielmehr eine Reihe von bewegten Aufnahmen atomarer Substrukturen und den dazugehöringen Prozessen. Existierende dritte Generation Synchrotronstrahlungsquellen werden an die neuen Herausforderungen angepasst: Verbesserungen an der Magnet-Optik sowie der Einbau modernster Beschleunigertechnologie ermöglichen die Erzeugung kürzester Pulse mit höchster Brillanz für zeitaufgelöste Experimente. Ein möglicher Kandidat für die Lichtquelle der nächsten Generation ist ein Linear-Beschleuniger mit Energierückgewinnung. Durch die Verwendung langer Beschleunigungsstrukturen kann es, selbst bei hohen Energien, nicht zur Ausbildung des Emittanzgleichgewichts wie in Speicherringen kommen. Durch die Verwendung Impulsabhängiger-Umlaufbahnen und der Rückgewinnung der Strahlenergie ist es mit `Energy Recovery Linac'' (ERL)-basierten Quellen energieeffizient möglich, hochenergetische Elektronen-Pulse im Femtosekundenbereich zu erzeugen. Die longitudinale Elekronstrahldynamik solcher ERLs ist eines der Hauptthemen dieser Arbeit. Umfangreiche Simulationen über die gesamte Maschine wurden im Rahmen der `Femto-Science Factory'' Lichtquellen Studie durchgeführt. Die Begrenzungen des Kurzpulsmodus Betriebes wurden untersucht und mit den Erwartungen verglichen. Besondere Aufmerksamkeit lag dabei auf den 6D Elektronenstrahleigenschaften, insbesondere auf der Vermeidung von Strahlaufweitungen, die mit der Erzeugung von Ultra-Kurzpulsen einhergehen können.Synchrotron light sources are entering a new era. No matter how elaborate, all the next generation proposals share a common necessity; the production of ultra-short electron bunches. There is an evolution in the field of science under investigation using the high peak brilliance generated from such bunches. The user community is demanding not just pictures but videos of atomic substructures and the processes that define them. Existing 3rd generation facilities are modifying their magnetic lattices and upgrading the acceleration schemes in order to keep up with this trend of generating short pulses with ultimate brilliance for time resolved experiments. A possible candidate for the next generation light source is one based on ERL technology. Using long linacs to accelerate to high energies overcomes the present limitation of emittance equilibrium in storage rings. By implementing independent arcs for acceleration and deceleration while recuperating the beams energy, ERL based sources are theoretically capable of efficiently producing high energy femtosecond long bunch lengths. The study of the longitudinal motion of the beam through single pass magnetic optic in combination with linacs is the main topic of this thesis. Dedicated start-to-end simulations in the framework of the Femto-Science Factory large scale light source are undertaken. The expectations and restrictions on the short pulse mode (SPM) operation are comprehensively examined in this work. Particular attention is given to the 6D electron beam properties and with it the beam degradation caused by the production of ultra-short bunches

Anterior segment topography and aberrations for clinical applications

En esta tesis se ha llevado a cabo el desarrollo de un Tomógrafo de Coherencia Óptica (OCT) para visualizar en alta resolución y cuantificar tridimensionalmente el segmento anterior del ojo y se ha adaptado el aberrómetro Trazado de Rayos Laser (LRT) para medir las aberraciones oculares en distintas condiciones: queratocono y su tratamiento con anillos intracorneales (ICRS), estimulando la acomodación y en pacientes con lentes intraoculares (IOL). En particular, (1) se analiza la geometría de la córnea y las aberraciones en pacientes con queratocono antes y después de la cirugía de ICRS, y se analiza la posición de los ICRS; (2) se evalúa por primera vez in vivo la topografía del cristalino con la acomodación; (3) se analiza por primera vez la posición tridimensional y el impacto visual de las IOL acomodativas; y (4) se analiza in vivo la aberración cromática longitudinal en pacientes con IOL.Instituto Universitario de Oftalmobiología Aplicad

Development of a new method for the wave optical propagation of ultrashort pulses through linear optical systems

The design and simulation of ultrashort pulse shaping systems require pulse propagation methods that take the combined effects of dispersion, diffraction, and system aberrations into account. In the conventional pulse propagation methods based on the spectrum of plane wave, usually large number of sampling points are needed for the correct Fourier transform operations due to the fast oscillating phase of the complex pulse field. In this work, I have developed an alternative pulse propagation method, based on the Gaussian pulsed beam decomposition, as an extension of the monochromatic Gaussian beam propagation method. Methods for the decomposition of an input pulse, with arbitrary spatial and temporal (spectral) profiles, into a set of elementary Gaussian pulsed beams are proposed. Algorithms for computing the spatio-temporal and spatio-spectral profiles of the propagated pulse as the phase correct superposition of individual Gaussian pulsed beams are developed. The proposed decomposition method allows the elementary Gaussian pulsed beams to have different parameters depending on the local spatial and spectral phase of the given input pulse which reduces the number of Gaussian pulsed beams required to decompose an input pulsed beam with a given accuracy. Furthermore, a new kind of beam called the truncated Gaussian beam, is introduced and combined with the conventional Gaussian beam decomposition method to enable decomposition of fields after hard apertures. The analytical propagation equation of the truncated Gaussian beam through a paraxial optical system is derived. Additionally, the application of the Gaussian beam decomposition method is extended to handle the propagation of vectorial fields. Several example calculations are presented to validate the proposed methods and show their application in propagating fields through optical systems which are rather complicated to model using the conventional methods

Adaptations of the human eye to reduce the impact of chromatic aberrations on vision

Sharpness and contrast of the retinal image are affected by two types of optical aberrations, monochromatic and polychromatic. Monochromatic aberrations result from imperfections in the refracting surfaces, while polychromatic aberrations result from the dispersion of light in the ocular media. Wavelength-dependent differences in focal lengths are referred to as longitudinal chromatic aberration (LCA) while differences in image position and image magnification result from transverse chromatic aberration (TCA). The primary objective of my PhD work is to further clarify the relationship between two chromatic aberrations, longitudinal chromatic aberration (LCA) and transverse chromatic aberration (TCA), and visual perception. I have studied the morphological and optical adaptations of the visual system that were developed in the course of evolution to cope with chromatic aberrations. Generally, transverse chromatic aberration (TCA) has been less studied even though it causes more loss in retinal image contrast. While LCA is similar in different eyes, TCA shows large inter-individual variability. It is not known which ocular variables determine this variability. Therefore, in project 1 I have measured chromatic differences in perceived image magnification (determined by TCA) in different subjects with a newly established psychophysical procedure and found that a major part of the inter-individual variance in CDM (64%) was explained by lens thickness. Since lens thickness increase with age, also TCA will increase. This study was published in the Journal of the Optical Society of America A, 2014. Due to longitudinal chromatic aberration (LCA), the focus of the image on the retina cannot be equally good at all wavelengths. Human eyes are about 2 D more myopic in blue light (450 nm) than in red (650 nm). For this reason, the retinal image in the fovea is typically in best focus for the mid- and long-wavelengths but severely out of focus for the blue (>1D). Probably for this reason, the short wavelength sensitive cones (the S-cones) are lacking from the foveal center, causing a “foveal blue scotoma”. I found that the foveal blue scotoma is highly variable among subjects but it is not known, why. Therefore, in project 2, I have studied the variables that might influence the appearance of the foveal blue scotoma: shape of the foveal pit and distribution of macular pigment. I found that the shape of the foveal pit is a strong predictor of the foveal blue scotoma - the steeper the foveal slopes, the larger the blue scotoma. Macular pigment distribution, on the other, gave rise to the percept of Maxwell’s spot, but was not correlated to the size of the blue scotoma. This study was published in Vision Research, 2015. My third project deals with new technology to measure LCA. In our laboratory we use routinely eccentric infrared photorefraction to measure refractive states in human and animal eye. The use 6 of infrared light has the advantage that the subject is not aware that is being measured and that pupils remain large which increases the signal-to-noise ratio. However eccenetric photorefraction could also provide information on LCA if it is used in white light. The differences in refractions measured in the R, G and B channel of the video camera should provide LCA but this technique was never established even though it would be a great advance to obtain LCA from single pictures of the eye. Therefore, in project 3, I studied the potential of polychromatic eccentric photorefraction in measuring LCA. I found that the calibration of photorefraction in white light is much more variable in different subjects, than in infrared light. The major reason was the large individual variability in fundal reflectance in visible light and less variability in the near infrared. Fundal reflectance has a major effect on the brightness of the pupil during the measurements. Because the technique uses a brightness slope in the pupil, and determines the gradient of pixel values, the slope of pupil brightness depends on the absolute pixel brightness. This finding explains a lot of the variability of photorefraction and will be of interest to researchers using this technique. The work was submitted to BOE in June 2015

A study of the application of adaptive optics (AO) in optical coherence tomography (OCT) and confocal microscopy for the purpose of high resolution imaging

A problem is presented when imaging the eye in that optical aberrations are introduced by tissues of the anterior eye such as the cornea and lens. Adaptive optics (AO) and scanning laser ophthalmoscopy (SLO) have been combined to detect and compensate for these aberrations through the use of one or more correcting devices. Di erent corrector options exist, such as a liquid crystal lens or a deformable mirror (DM), such as that used in this thesis. This study seeks to use the ability of the DM to add focus/defocus aberrations to the closed loop AO system. This procedure could allow for dynamic focus control during generation of B-scan images using spectral domain optical coherence tomography (SD-OCT), where typically this is only possible using slower time domain techniques. The confocal gate scanning is controlled using the focus altering aberrations created by changing the shape of the deformable mirror. Using the novel master-slave interferometry method, multiple live en-face images can be acquired simultaneously. In this thesis, application of this method to an AO system is presented whereby en-face images may be acquired at multiple depths simultaneously. As an extension to this research, an OCT despeckle method is demonstrated. Further to this work is the investigation of the role in AO for optimisation of optical systems without the requirement for direct aberration measurement. Towards this end, genetic algorithms (GA) may be employed to control the DM in an iterative process to improve the coupling of light into fibre