Over the past several years, experiments in adaptive optics involving multiple natural and laser guide stars have been carried out at the 1.55 m Kuiper telescope and the 6.5 m MMT telescope. The astronomical imaging improvement anticipated from both ground-layer and tomographic adaptive optics has been calculated. Ground-layer adaptive optics will reduce the effects of atmospheric seeing, increasing the resolution and sensitivity of astronomical observations over wide fields. Tomographic adaptive optics will provide diffraction-limited imaging along a single line of sight, increasing the amount of sky coverage available to adaptive optics correction.A new facility class wavefront sensor has been deployed at the MMT which will support closed-loop adaptive optics correction using a constellation of five Rayleigh laser guide stars and the deformable F/15 secondary mirror. The adaptive optics control loop was closed for the first time around the focus signal from all five laser signals in July of 2007, demonstrating that the system is working properly. It is anticipated that the full high-order ground-layer adaptive optics loop, controlled by the laser signals in conjunction with a tip/tilt natural guide star, will be closed in September 2007, with the imaging performance delivered by the system optimized and evaluated.The work here is intended to be both its own productive scientific endeavor for the MMT, but also as a proof of concept for the advanced adaptive optics systems designed to support observing at the Large Binocular Telescope and future extremely large telescopes such as the Giant Magellan Telescope.

The human eye suffers various optical aberrations that degrade the retinal image. These aberrations include defocus and astigmatism, as well as the higher order aberrations that also play an important role in our vision. The optics of the eye are not static, but are continuously fluctuating. The work reported in this thesis has studied the nature of the microfluctuations of the wavefront aberrations of the eye and has investigated factors that influence the microfluctuations. The fluctuations in the ocular surface of the eye were investigated using high speed videokeratoscopy which measures the dynamics of the ocular surface topography. Ocular surface height difference maps were computed to illustrate the changes in the tear film in the inter-blink interval. The videokeratoscopy data was used to derive the ocular surface wavefront aberrations up to the 4th radial order of the Zernike polynomial expension. We examined the ocular surface dynamics and temporal changes in the ocular surface wavefront aberrations in the inter-blink interval. During the first 0.5 sec following a blink, the tear thickness at the upper edge of the topography map appeared to thicken by about 2 microns. The influence of pulse and instantaneous pulse rate on the microfluctuations in the corneal wavefront aberrations was also investigated. The fluctuations in ocular surface wavefront aberrations were found to be uncorrelated with the pulse and instantaneous heart rates. In the clinical measurement of the ocular surface topography using videokeratoscopy, capturing images 2 to 3 seconds after a blink will result in more consistent results. To investigate fluctuations in the wavefront aberrations of the eye and their relation to pulse and respiration frequencies we used a wavefront sensor to measure the dynamics of the aberrations up to the Zernike polynomial 4th radial order. Simultaneously, the subject's pulse rate was measured, from which the instantaneous heart rate was derived. An auto-regressive process was used to derive the power spectra of the Zernike aberration signals, as well as pulse and instantaneous heart rate signals. Linear regression analysis was performed between the frequency components of Zernike aberrations and the pulse and instantaneous heart rate frequencies. Cross spectrum density and coherence analyses were also applied to investigate the relation between fluctuations of wavefront aberrations and pulse and instantaneous heart rate. The correlations between fluctuations of individual Zernike aberrations were also determined. A frequency component of all Zernike aberrations up to the 4th radial order was found to be significantly correlated with the pulse frequency (all > 2R0.51, p<0.02), and a frequency component of 9 out of 12 Zernike aberrations was also significantly correlated with instantaneous heart rate frequency (all>2R0.46, p<0.05). The major correlations among Zernike aberrations occurred between second order and fourth order aberrations with the same angular frequencies. Higher order aberrations appear to be related to the cardiopulmonary system in a similar way to that reported for the accommodation signal and pupil fluctuations. A wavefront sensor and high speed videokeratoscopy were used to investigate the contribution of the ocular surface, the effect of stimulus vergence, and refractive error on the microfluctuations of the wavefront aberrations of the eye. The fluctuations of the Zernike wavefront aberrations were quantified by their variations around the mean and using power spectrum analysis. Integrated power was determined in two regions: 0.1 Hz ─ 0.7 Hz (low frequencies) and 0.8 Hz ─ 1.8 Hz (high frequencies). Changes in the ocular surface topography were measured using high speed videokeratoscopy and variations in the ocular wavefront aberrations were calculated. The microfluctuations of wavefront aberrations in the ocular surface were found to be small compared with the microfluctuations of the wavefront aberrations in the total eye. The variations in defocus while viewing a closer target at 2 D and 4 D stimulus vergence were found to be significantly greater than variations in defocus when viewing a far target. This increase in defocus fluctuations occurred in both the low and high frequency regions (all p<0.001) of the power spectra. The microfluctuations in astigmatism and most of the 3rd order and 4th order Zernike wavefront aberrations of the total eye were found to significantly increase with the magnitude of myopia. The experiments reported in this thesis have demonstrated the characteristics of the microfluctuations of the wavefront aberrations of the eye and have shown some of the factors that can influence the fluctuations. Major fluctuation frequencies of the eye's wavefront aberrations were shown to be significantly correlated with the pulse and instantaneous heart rate frequencies. Fluctuations in the ocular surface wavefront aberrations made a small contribution to those of the total eye. Changing stimulus vergence primarily affected the fluctuations of defocus in both low and high frequency components. Variations in astigmatism and most 3rd and 4th order aberrations were associated with refractive error magnitude. These findings will aid our fundamental understanding of the complex visual optics of the human eye and may allow the opportunity for better dynamic correction of the aberrations with adaptive optics.

Direct imaging of exoplanets requires establishing and maintaining a high-contrast dark field (DF) within the science image to a high degree of precision (10(-10)). Current approaches aimed at establishing the DF, such as electric field conjugation (EFC), have been demonstrated in the lab and have proven capable of high-contrast DF generation. The same approaches have been considered for the maintenance of the DF as well. However, these methods rely on phase diversity measurements, which require field modulation; this interrupts the DF and consequently competes with the science acquisition. We introduce and demonstrate spatial linear dark field control (LDFC) as an alternative technique by which the high-contrast DF can be maintained without modulation. Once the DF has been established by conventional EFC, spatial LDFC locks the high-contrast state of the DF by operating a closed loop around the linear response of the bright field (BF) to wavefront variations that modify both the BF and the DF. We describe the fundamental operating principles of spatial LDFC and provide numerical simulations of its operation as a DF stabilization technique that is capable of wavefront correction within the DF without interrupting science acquisition. (c) The Authors.

La nécessité de la montée en puissance, crête et moyenne, des chaines lasers hyper intenses a fait émerger un nouveau type d'architecture. Le principe consiste à combiner de manière cohérente un grand nombre de lasers élémentaires les plus simples et robustes possible. La difficulté de la montée en puissance est donc reportée essentiellement sur le système de recombinaison. Plusieurs laboratoires à travers le monde ont ainsi décidé de s'impliquer dans cette voie. S'il existe des concepts variés pour la boucle d'asservissement, il n'y a pas pour l'instant, à notre connaissance, de développement d'un moyen de métrologie absolue de la qualité du front d'onde final, et donc de la recombinaison. Or celui-ci est fondamental pour deux moments particuliers de la conception de ces nouvelles architectures.Dans un premier temps, il est nécessaire de connaître la nature, l'amplitude et la fréquence des défauts de phase en boucle ouverte afin de bien spécifier l'architecture de la tête optique et le système de contrôle/commande. Puis, lorsque la chaîne est pleinement opérationnelle, en boucle fermée, la qualité de la recombinaison doit être évaluée. L'objet de cette thèse est de proposer un nouvel interféromètre adapté à ces deux besoins, c'est-à-dire capable d'encaisser de fortes dynamiques et d'avoir en même temps des capacités de mesure absolue de très grandes précision et justesse, à haute cadence, afin de mesurer et d'analyser le front d'onde résultant de la combinaison des différents lasers sur toute la phase de conception de ces lasers, en boucle ouverte comme en boucle fermée. / The need for the rise in power, peak and medium, of hyper intense laser chains has led to the emergence of a new type of architecture. The principle is to consistently combine a large number of the simplest and most robust elementary lasers possible. The difficulty of ramping up is therefore mainly transferred to the recombination system. Several laboratories around the world have thus decided to get involved in this path. If there are various concepts for the servo loop, there is currently, to our knowledge, no development of a means of absolute metrology of the quality of the final wavefront, and therefore of recombination. This is fundamental for two particular moments in the design of these new architectures.First, it is necessary to know the nature, amplitude and frequency of open loop phase faults in order to properly specify the optical head architecture and the control/command system. Then, when the chain is fully operational, in closed loop, the quality of the recombination must be evaluated. The purpose of this thesis is to propose a new interferometer adapted to these two needs, i.e. capable of withstanding strong dynamics and at the same time having absolute measurement capabilities of very high precision and accuracy, at high cadence, in order to measure and analyze the wavefront resulting from the combination of the different lasers over the entire design phase of these lasers, in open loop as in closed loop.

Nowadays, metamaterials have found their places in different branches of wave physics ranging from electromagnetics to acoustic waves. Acoustic metamaterials are sub-wavelength structures in which their effective acoustic properties are dominated by their structural shape rather than their constitutive materials. In recent years, acoustic metamaterials have gained increasing interest due to numerous promising applications such as sub-wavelength imaging, perfect absorption, acoustic cloaking, etc. The focus of the work herein is to leverage acoustic metamaterial/metasurface structures to manipulate the acoustic wavefront to pave the road for future applications of the metamaterials. In the first part of the work, the metamaterial structure is introduced, which can be leveraged for better manipulation of the transmitted wave by modulating both phase and amplitude. Initially, a general bound on the transmission phase/amplitude space for the case of arbitrary metasurface has been presented and subsequently, the necessary condition for the complete modulation of the transmitted wave is investigated. Next, a horn-like space coiling metamaterial is introduced, which satisfied the aforementioned condition and enabled us to simultaneously modulate both the phase and amplitude of the transmitted wave. Furthermore, our initial efforts toward designing a metamaterial capable of real-time phase modulation with relatively constant amplitude will be discussed. In the second part of this work, a novel metamaterial-based methodology is presented for the design of the air-permeable acoustic silencer. In this work, the concept of the bilayer-transverse metamaterial is introduced, and its functionality for silencing the acoustic wave is demonstrated. Furthermore, it is shown that the methodology presented herein essentially does not limit the ratio of the open area, and ultra-open metamaterial silencers may be designed. Eventually, based on the presented methodology, the ultra-open metamaterial featuring nearly 60% open area is designed, and silencing capacity of about 94% at the targeted frequency is experimentally realized. In the last part of this work, the behavior of a locally resonant class of acoustic metamaterial in the non-Rayleigh regime has been explored. Elaborately, it is demonstrated that in the case of spherical inclusion in a matrix material, large variation in the effective acoustic impedance emerges near the inclusion’s Eigenmode. Eventually, the potential application of this novel phenomenon in the non-destructive evaluation (NDE) and ultrasound imaging is discussed. / 2020-08-09T00:00:00Z

京都大学 / 0048 / 新制・課程博士 / 博士(人間健康科学) / 甲第21037号 / 人健博第53号 / 新制||人健||4(附属図書館) / 京都大学大学院医学研究科人間健康科学系専攻 / (主査)教授 杉本 直三, 教授 精山 明敏, 教授 安達 泰治 / 学位規則第4条第1項該当 / Doctor of Human Health Sciences / Kyoto University / DFAM

Epilepsy is a disease affecting millions of people worldwide. Despite over 50 years of research, the mechanisms that generate and sustain ictal discharges, a key neural hallmark of seizures, remain unknown. While once thought to be caused by hypersynchronous neuronal firing, we now recognize that the activity underlying ictal discharges is much more complex. With the development of microelectrode arrays (MEAs) suitable for use in humans, it is possible to observe neural activity at fine spatiotemporal scales in human patients with epilepsy. However, the diversity of seizure characteristics and limited patient population has led to a number of conflicting observations and theories. The purpose of this work is to elucidate mechanisms underlying ictal discharges in humans by applying statistical analyses and computational modeling to MEA recordings from human patients with epilepsy. We approach this aim in two projects. In the first project, we unify two seemingly conflicting theories surrounding cortical sources of ictal discharges. According to the ictal wavefront theory, ictal discharges are seeded at an expanding narrow front of high neuronal firing that delineates the boundary between regions of cortex with compromised functionality, and surrounding territory where the seizure is observable in electrical recordings, but cortical function remains intact. A second theory posits that discharges are predominantly seeded from a stationary localized cortical source. The two theories are based on observations from MEA recordings of seizures in two different small cohorts of patients. In this project, we analyze and model the discharge propagation patterns in a combined dataset from both cohorts. We show that discharges are seeded at the ictal wavefront in addition to other–possibly stationary–locations. In the second project, we characterize spatiotemporal patterns in the secondary transients of complex ictal discharges. Electrographic recordings of ictal discharges often have complex waveforms. Existing analyses focus on the spatiotemporal dynamics of the first, high-amplitude transient. In this project, we establish that ictal discharges often comprise multiple transients separated by ≈60 ms. Surprisingly, and contrary to our initial hypothesis, we find that individual transients within a complex discharge may propagate with different speeds, suggesting that different mechanisms are involved in the propagation of different transients.

En microscopie, savoir focaliser la lumière à l’échelle micrométrique est déterminant. Dans les tissus biologiques néanmoins, les inhomogénéités du milieu diffusent la lumière, empêchant toute focalisation au-delà d’une profondeur de l’ordre du millimètre. Des techniques de façonnage de front d’onde ont été développées afin de pré-compenser la distorsion du faisceau lumineux induite par la propagation à travers un milieu diffusant. Pour parvenir à focaliser la lumière à l’intérieur même du milieu diffusant, l’enjeu est de mesurer l’intensité lumineuse en profondeur de manière non invasive. Nous proposons d’utiliser l’effet photoacoustique pour sonder cette intensité. Une structure optiquement absorbante éclairée par une impulsion lumineuse émet en effet un signal ultrasonore, dont l’amplitude est proportionnelle à l’intensité lumineuse. Ces ultrasons se propagent de façon quasi-balistique dans les tissus mous et peuvent donc être détectés à l’aide d’un transducteur acoustique externe. Cette mesure permet donc de déterminer l’intensité lumineuse éclairant l’absorbeur. Nous avons montré qu’il était possible d’utiliser l'imagerie photoacoustique pour mesurer la matrice de transmission d’un échantillon diffusant. Cette caractérisation nous permet de focaliser la lumière sur des structures absorbantes et de sonder des propriétés mésoscopiques du milieu diffusant. Nous avons montré que la large bande spectrale des signaux photoacoustiques permet d’améliorer la focalisation. Enfin, nous avons montré que l’utilisation d’une source de lumière cohérente permet de pallier certains artefacts de l’imagerie photoacoustique, ainsi que de franchir la limite de résolution acoustique. / Light focusing is a crucial requirement for high resolution optical imaging. In biological tissue though, refractive index inhomogeneities scatter light, preventing any focusing beyond one millimeter. Wavefront shaping techniques have been recently developed to partially compensate for light scattering after propagation through a scattering medium. These techniques require a measurement of the light intensity at the target point. These techniques hold much promise for performing wavefront correction in order to focus light deep inside scattering media. This would require a non-invasive measure of the light intensity at depth. In this PhD study, we propose to use the photoacoustic effect for such task. An optically absorbing structure under pulsed illumination indeed generates ultrasonic waves, whose amplitude is proportional to the absorbed light intensity. These ultrasounds mostly propagate in a ballistic way, and can therefore be detected with an external transducer. We have shown that photoacoustic imaging could be used to measure the transmission matrix of a scattering sample, enabling to focus light on absorbing structures as well as to retrieve mesoscopic properties of the medium. We have shown that the broadband spectral content of the photoacoustic signals can be harnessed to improve the focusing performances. Finally, we demonstrated that coherent illumination could be used to remove fundamentals artefacts, as well as to break the acoustic resolution limit of conventional deep tissue photoacoustic imaging.

Imager une exo-terre à proximité d’une étoile est une tâche complexe : le signal de la planète est noyé dans le flux immense de l’étoile, très proche. Doivent donc être combinés :- de grands télescopes spatiaux segmentés. La segmentation du miroir primaire facilite le transport mais crée des erreurs liées à l’alignement.- un coronographe, permettant d’éteindre la lumière stellaire. - enfin, toute aberration optique crée un résidu lumineux nuisible dans l’image. La mesure et le contrôle des aberrations d’un système coronographique, notamment celles liées à la segmentation du télescope, sont donc primordiaux et constituent le sujet de ma thèse.Tout d’abord, j’ai développé PASTIS, un modèle simplifié du contraste d’un coronographe en présence d’une pupille segmentée, permettant d’analyser facilement les performances pour contraindre les aberrations optiques lors du design de l’instrument. PASTIS prend en compte les spécificités des instruments : structure de la pupille, aberrations optiques dues à la segmentation, coronographe. Je l’ai appliqué au télescope LUVOIR afin d’analyser les modes limitant le contraste et ainsi mieux répartir les contraintes sur les segments. Par la suite, j’ai travaillé sur l’analyse de front d’onde coronographique en présence d’un télescope segmenté sur le banc expérimental HiCAT avec une première démonstration de l’analyseur COFFEE permettant de reconstruire les erreurs de phasage avec une grande précision. Enfin, j’ai mené une analyse comparative des multiples méthodes de contrôle de front d’onde existantes et validé l’une d’elles (Dark Hole Non Linéaire) expérimentalement dans un cadre simplifié sur le banc MITHIC du LAM / Direct imaging of exo-Earths is extremely complex: the star is by far brighter and very close to the planet. Several tools have to be combined:- a giant primary mirror. For manufacturing and transportation reasons, we tend to use segmented mirrors, ie. mirrors made of smaller mirrors but that have to be well-aligned and stabilised.- a coronagraph, enabling to remove the starlight.- the smallest residual wavefront aberration into residual light that decreases the image quality. The measurement and control of the aberrations, including the ones due to the telescope segmentation, are crucial and consist in the topic of my thesis.First, I developed PASTIS, a model of the contrast of a coronagraphic system in presence of a segmented pupil, enabling to analyze the performance to set up constraints on the optical aberrations during the instrument design. PASTIS takes into account the specificities of high-contrast instruments: pupil structure, optical aberrations due to the segmentation, coronagraph. I applied it to the LUVOIR telescope to analyze the main modes limiting the contrast and therefore optimizing the repartition of the constraints on the segments. In parallel, I worked on the analysis of the coronagraphic wavefront in presence of a segmented telescope on the experimental testbed called HiCAT, with a first demonstration of the COFFEE sensor enabling to reconstruct phasing errors with a high precision.Eventually, I ran a comparative analysis of existing methods of wavefront control and experimentally validated one of them (Non Linear Dark Hole) in a simplified case on the MITHIC testbed at LAM

DICE, a Swedish game company, wanted a more realistic water simulation. Currently, most large scale water simulations used in games are based upon ocean simulation technology. These techniques falter when used in other scenarios, such as coastlines. In order to produce a more realistic simulation, a new one was created based upon the water simulation technique "Wavefront Parameter Interpolation". This technique involves a rather extensive preprocess that enables ocean simulations to have interactions with the terrain. This paper is about optimizing the current implementation of DICE's water simulation. The goal is to achieve better runtime GPU performance. After implementing various optimizations, a speedup of roughly 4-6x was achieved. Performance was evaluated on the PlayStation 4 gaming console. / DICE, ett svenskt spelföretag, ville ha en mer realistisk vattensimulering. Det flesta storskalna vattensimuleringar som används i spel idag är baserade på havsvattensimuleringstekniker. Dessa tekniker fungerar inte lika bra i andra scenarier, som t.ex. kustlinjer. För att kunna få en mer realistisk simulation, skapades en ny simulation baserad på vattensimuleringstekniken Wavefront Parameter Interpolation. Denna simuleringsteknik involverar en lång förprocess som ger havsvattensimuleringar möjligheten att interagera med terräng. Denna uppsats handlar om att optimera den nuvarande implementationen av DICEs vattensimulering. Målet är att få bättre grafikprestanda under körtid. Efter att olika optimiseringar hade implementerats, blev programmet 4-6x gånger snabbare. Prestandan utvärderades på spelkonsolen PlayStation 4.