Laser beam control, combining, and propagation in atmospheric turbulence

This dissertation is concerned with the control, combining, and propagation of laser beams through a turbulent atmosphere. In the first part we consider adaptive optics: the process of controlling the beam based on information of the current state of the turbulence. If the target is cooperative and provides a coherent return beam, the phase measured near the beam transmitter and adaptive optics can, in principle, correct these fluctuations. However, for many applications, the target is uncooperative. In this case, we show that an incoherent return from the target can be used instead. Using the principle of reciprocity, we derive a novel relation between the field at the target and the scattered field at a detector. We then demonstrate through simulation that an adaptive optics system can utilize this relation to focus a beam through atmospheric turbulence onto a rough surface. In the second part we consider beam combining. To achieve the power levels needed for directed energy applications it is necessary to combine a large number of lasers into a single beam. The large linewidths inherent in high-power fiber and slab lasers cause random phase and intensity fluctuations occurring on sub-nanosecond time scales. We demonstrate that this presents a challenging problem when attempting to phase-lock high-power lasers. Furthermore, we show that even if instruments are developed that can precisely control the phase of high-power lasers; coherent combining is problematic for DE applications. The dephasing effects of atmospheric turbulence typically encountered in DE applications will degrade the coherent properties of the beam before it reaches the target. Finally, we investigate the propagation of Bessel and Airy beams through atmospheric turbulence. It has been proposed that these quasi-non-diffracting beams could be resistant to the effects of atmospheric turbulence. However, we find that atmospheric turbulence disrupts the quasi-non-diffracting nature of Bessel and Airy beams when the transverse coherence length nears the initial aperture diameter or diagonal respectively. The turbulence induced transverse phase distortion limits the effectiveness of Bessel and Airy beams for applications requiring propagation over long distances in the turbulent atmosphere.

the plenoptic sensor

In this thesis, we will introduce the innovative concept of a plenoptic sensor that can determine the phase and amplitude distortion in a coherent beam, for example a laser beam that has propagated through the turbulent atmosphere.. The plenoptic sensor can be applied to situations involving strong or deep atmospheric turbulence. This can improve free space optical communications by maintaining optical links more intelligently and efficiently. Also, in directed energy applications, the plenoptic sensor and its fast reconstruction algorithm can give instantaneous instructions to an adaptive optics (AO) system to create intelligent corrections in directing a beam through atmospheric turbulence. The hardware structure of the plenoptic sensor uses an objective lens and a microlens array (MLA) to form a mini “Keplerian” telescope array that shares the common objective lens. In principle, the objective lens helps to detect the phase gradient of the distorted laser beam and the microlens array (MLA) helps to retrieve the geometry of the distorted beam in various gradient segments. The software layer of the plenoptic sensor is developed based on different applications. Intuitively, since the device maximizes the observation of the light field in front of the sensor, different algorithms can be developed, such as detecting the atmospheric turbulence effects as well as retrieving undistorted images of distant objects. Efficient 3D simulations on atmospheric turbulence based on geometric optics have been established to help us perform optimization on system design and verify the correctness of our algorithms. A number of experimental platforms have been built to implement the plenoptic sensor in various application concepts and show its improvements when compared with traditional wavefront sensors. As a result, the plenoptic sensor brings a revolution to the study of atmospheric turbulence and generates new approaches to handle turbulence effect better.

Two roads to planet detection

One of the most exciting discoveries in astrophysics of the last last decade is of the sheer diversity of planetary systems. These include "hot Jupiters", giant planets so close to their host stars that they orbit once every few days; "Super-Earths", planets with sizes intermediate to those of Earth and Neptune, of which no analogs exist in our own solar system; multi-planet systems with planets smaller than Mars to larger than Jupiter; planets orbiting binary stars; free-floating planets flying through the emptiness of space without any star; even planets orbiting pulsars. Despite these remarkable discoveries, the field is still young, and there are many areas about which precious little is known. In particular, we don't know the planets orbiting Sun-like stars nearest to our own solar system, and we know very little about the compositions of extrasolar planets. This thesis provides developments in those directions, through two instrumentation projects.

The first chapter of this thesis concerns detecting planets in the Solar neighborhood using precision stellar radial velocities, also known as the Doppler technique. We present an analysis determining the most efficient way to detect planets considering factors such as spectral type, wavelengths of observation, spectrograph resolution, observing time, and instrumental sensitivity. We show that G and K dwarfs observed at 400-600 nm are the best targets for surveys complete down to a given planet mass and out to a specified orbital period. Overall we find that M dwarfs observed at 700-800 nm are the best targets for habitable-zone planets, particularly when including the effects of systematic noise floors caused by instrumental imperfections. Somewhat surprisingly, we demonstrate that a modestly sized observatory, with a dedicated observing program, is up to the task of discovering such planets.

We present just such an observatory in the second chapter, called the "MINiature Exoplanet Radial Velocity Array," or MINERVA. We describe the design, which uses a novel multi-aperture approach to increase stability and performance through lower system etendue, as well as keeping costs and time to deployment down. We present calculations of the expected planet yield, and data showing the system performance from our testing and development of the system at Caltech's campus. We also present the motivation, design, and performance of a fiber coupling system for the array, critical for efficiently and reliably bringing light from the telescopes to the spectrograph. We finish by presenting the current status of MINERVA, operational at Mt. Hopkins observatory in Arizona.

The second part of this thesis concerns a very different method of planet detection, direct imaging, which involves discovery and characterization of planets by collecting and analyzing their light. Directly analyzing planetary light is the most promising way to study their atmospheres, formation histories, and compositions. Direct imaging is extremely challenging, as it requires a high performance adaptive optics system to unblur the point-spread function of the parent star through the atmosphere, a coronagraph to suppress stellar diffraction, and image post-processing to remove non-common path "speckle" aberrations that can overwhelm any planetary companions.

To this end, we present the "Stellar Double Coronagraph," or SDC, a flexible coronagraphic platform for use with the 200" Hale telescope. It has two focal and pupil planes, allowing for a number of different observing modes, including multiple vortex phase masks in series for improved contrast and inner working angle behind the obscured aperture of the telescope. We present the motivation, design, performance, and data reduction pipeline of the instrument. In the following chapter, we present some early science results, including the first image of a companion to the star delta Andromeda, which had been previously hypothesized but never seen.

A further chapter presents a wavefront control code developed for the instrument, using the technique of "speckle nulling," which can remove optical aberrations from the system using the deformable mirror of the adaptive optics system. This code allows for improved contrast and inner working angles, and was written in a modular style so as to be portable to other high contrast imaging platforms. We present its performance on optical, near-infrared, and thermal infrared instruments on the Palomar and Keck telescopes, showing how it can improve contrasts by a factor of a few in less than ten iterations.

One of the large challenges in direct imaging is sensing and correcting the electric field in the focal plane to remove scattered light that can be much brighter than any planets. In the last chapter, we present a new method of focal-plane wavefront sensing, combining a coronagraph with a simple phase-shifting interferometer. We present its design and implementation on the Stellar Double Coronagraph, demonstrating its ability to create regions of high contrast by measuring and correcting for optical aberrations in the focal plane. Finally, we derive how it is possible to use the same hardware to distinguish companions from speckle errors using the principles of optical coherence. We present results observing the brown dwarf HD 49197b, demonstrating the ability to detect it despite it being buried in the speckle noise floor. We believe this is the first detection of a substellar companion using the coherence properties of light.

Near-infrared polarimetry in the galactic center. On properties of Sagittarius A* and a dusty S-cluster object

Near-infrared polarimetry observation is a powerful tool to study the central sources at the center of the Milky Way. My aim of this thesis is to analyze the polarized emission present in the central few light years of the Galactic Center region, in particular the non-thermal polarized emission of Sagittarius~A* (Sgr~A*), the electromagnetic manifestation of the super-massive black hole, and the polarized emission of an infrared-excess source in the literature referred to as DSO/G2. This source is in orbit about Sgr~A*. In this thesis I focus onto the Galactic Center observations at $\lambda=2.2~\mu m$ ($K_\mathrm{s}$-band) in polarimetry mode during several epochs from 2004 to 2012. The near-infrared polarized observations have been carried out using the adaptive optics instrument NAOS/CONICA and Wollaston prism at the Very Large Telescope of ESO (European Southern Observatory). Linear polarization at 2.2 $\mu m$, its flux statistics and time variation, can be used to constrain the physical conditions of the accretion process onto the central super-massive black hole. I present a statistical analysis of polarized $K_\mathrm{s}$-band emission from Sgr~A* and investigate the most comprehensive sample of near-infrared polarimetric light curves of this source up to now. I find several polarized flux excursions during the years and obtain an exponent of about 4 for the power-law fitted to polarized flux density distribution of fluxes above 5~mJy. Therefore, this distribution is closely linked to the single state power-law distribution of the total $K_\mathrm{s}$-band flux densities reported earlier by us. I find polarization degrees of the order of 20\%$\pm$10\% and a preferred polarization angle of $13^o\pm15^o$. Based on simulations of polarimetric measurements given the observed flux density and its uncertainty in orthogonal polarimetry channels, I find that the uncertainties of polarization parameters under a total flux density of $\sim 2\,{\mathrm{mJy}}$ are probably dominated by observational uncertainties. At higher flux densities there are intrinsic variations of polarization degree and angle within rather well constrained ranges. Since the emission is most likely due to optically thin synchrotron radiation, the obtained preferred polarization angle is very likely reflecting the intrinsic orientation of the Sgr~A* system i.e. an accretion disk or jet/wind scenario coupled to the super-massive black hole. Our polarization statistics show that Sgr~A* must be a stable system, both in terms of geometry, and the accretion process. I also investigate an infrared-excess source called G2 or Dusty S-cluster Object (DSO) moving on a highly eccentric orbit around the Galaxy's central black hole, Sgr~A*. I use for the first time the near-infrared polarimetric imaging data to determine the nature and the properties of DSO and obtain an improved $K_\mathrm{s}$-band identification of this source in median polarimetry images of different observing years. The source starts to deviate from the stellar confusion in 2008 data and it does not show a flux density variability based on our data set. Furthermore, I measure the polarization degree and angle of this source and conclude based on the simulations on polarization parameters that it is an intrinsically polarized source with a varying polarization angle as it approaches Sgr~A* position. I use the interpretation of the DSO polarimetry measurements to assess its possible properties.

Étude de la dynamique du ferrofluide appliquée sur une surface générée par plusieurs actionneurs

Le sujet de cette thèse est la caractérisation dynamique d’une surface générée par plusieurs actionneurs d’un miroir ferrofluidique intégré dans un montage d’optique adaptative. Elle conclut un projet de doctorat au sein du groupe Borra s’étant échelonné sur 4 années. Un bref portrait général de l’optique adaptative est d’abord présenté, suivi d’une section sur la théorie du contrôle. Les types de contrôleurs y sont abordés, soit PID et surcharge. L’effet de la viscosité sur la réponse dynamique du système, ainsi que les analyseurs de front d’onde utilisés sont ensuite expliqués. La section résultats est subdivisée en plusieurs sous-sections ordonnées de façon chronologique. Dans un premier temps, il est question des résultats obtenus dans le cadre d’une caractérisation d’un nouveau miroir de 91 actionneurs fabriqué au sein du groupe. Il est ensuite question des résultats obtenus avec diverses techniques telles le PSD et l’imagerie déclenchée. Il y aura toute une section sur les résultats en vitesse, en fonction de la viscosité du liquide, suivie d’une section sur les simulations réalisées avec Simulink afin de bien cibler les limites du système. Les résultats portant sur la technique de surcharge des actionneurs seront ensuite présentés avec des projections futures. La dernière partie de cette thèse portera sur une innovation apportée par un autre membre du groupe. Nous parlerons de la déposition d’une membrane élastomère réfléchissante et de ses effets sur la dynamique du système.

Exploring the internal kinematics of Galactic Globular Cluster cores

Globular clusters (GCs) are traditionally described as simple quasi-relaxed non-rotating stellar systems, characterized by spherical symmetry and isotropy in velocity space. However, recent studies have shown deviations from isotropic velocity distributions and significant internal rotation in many GCs, suggesting that their internal structure and kinematics are more complex than previously thought. The aim of this thesis is to investigate the internal kinematics of Galactic Globular Clusters (GGCs) as part of the Multi-Instrument Kinematic Survey (MIKiS), which exploits the capabilities of different ESO-VLT spectrographs to obtain comprehensive velocity dispersion (VD) and rotation profiles of GGCs. Moreover, this thesis has the particular goal of unraveling the kinematics of GC cores, which are still largely unexplored, by taking advantage of the exceptional spatial resolution of the adaptive-optics assisted integral-field spectrograph MUSE/NFM. The thesis presents a thorough kinematic study of three GGCs NGC 1904, NGC 6440, and NGC 6569. By combining the data sets acquired with four different spectrographs, we obtained the radial velocity (RV) of more than 1000 individual stars in each cluster, sampling from the innermost to the outermost regions. This allowed us to obtain the entire VD profile of each cluster and exclude the presence of an intermediate-mass black hole in the core of NGC 1904, at odds with previous findings obtained from integrated-light spectra. The studies also revealed signatures of internal rotation in each of the GCs studied. These results, supported by those of N-body simulations, prove that GCs were born with a significant initial rotation that they gradually lost through internal two-body relaxation and angular momentum loss carried away by escaping stars. Furthermore, we derived the structural parameters of NGC 6440 and NGC 6569, obtaining a comprehensive overview of the internal kinematics and structure of these GCs, which is necessary to properly reconstruct the evolutionary history of these systems.

Dengue Virus Type 3 Adaptive Changes during Epidemics in Sao Jose de Rio Preto, Brazil, 2006-2007

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Multifilter rotating shadowband radiometer calibration for spectral aerosol optical depth retrievals over Sao Paulo City, Brazil

Multifilter rotating shadowband radiometer (MFRSR) calibration values for aerosol optical depth (AOD) retrievals were determined by means of the general method formulated by Forgan [Appl. Opt. 33, 4841 (1994)] at a polluted urban site. The obtained precision is comparable with the classical method, the Langley plot, applied on clean mountaintops distant of pollution sources. The AOD retrieved over Sao Paulo City with both calibration procedures is compared with the Aerosol Robotic Network data. The observed results are similar, and, except for the shortest wavelength (415 nm), the MFRSR`s AOD is systematically overestimated by similar to 0.03. (c) 2008 Optical Society of America.

NEX-LMS: A novel adaptive control scheme for harmonic sound quality control

This paper presents a novel adaptive control scheme. with improved convergence rate, for the equalization of harmonic disturbances such as engine noise. First, modifications for improving convergence speed of the standard filtered-X LMS control are described. Equalization capabilities are then implemented, allowing the independent tuning of harmonics. Eventually, by providing the desired order vs. engine speed profiles, the pursued sound quality attributes can be achieved. The proposed control scheme is first demonstrated with a simple secondary path model and, then, experimentally validated with the aid of a vehicle mockup which is excited with engine noise. The engine excitation is provided by a real-time sound quality equivalent engine simulator. Stationary and transient engine excitations are used to assess the control performance. The results reveal that the proposed controller is capable of large order-level reductions (up to 30 dB) for stationary excitation, which allows a comfortable margin for equalization. The same holds for slow run-ups ( > 15s) thanks to the improved convergence rate. This margin, however, gets narrower with shorter run-ups (<= 10s). (c) 2010 Elsevier Ltd. All rights reserved.

Experimental investigation on adaptive robust controller designs applied to a free-floating space manipulator

This paper aims to formulate and investigate the application of various nonlinear H(infinity) control methods to a fiee-floating space manipulator subject to parametric uncertainties and external disturbances. From a tutorial perspective, a model-based approach and adaptive procedures based on linear parametrization, neural networks and fuzzy systems are covered by this work. A comparative study is conducted based on experimental implementations performed with an actual underactuated fixed-base planar manipulator which is, following the DEM concept, dynamically equivalent to a free-floating space manipulator. (C) 2011 Elsevier Ltd. All rights reserved.

In situ apoptosis of adaptive immune cells and the cellular escape of rabies virus in CNS from patients with human rabies transmitted by Desmodus rotundus

The aim of the current study was to investigate the apoptosis of neurons, astrocytes and immune cells from human patients that were infected with rabies virus by vampire bats bite. Apoptotic neurons were identified by their morphology and immune cells were identified using double immunostaining. There were very few apoptotic neurons present in infected tissue samples, but there was an increase of apoptotic infiltrating CD4+ and TCD8+ adaptive immune cells in the rabies infected tissue. No apoptosis was present in NK, macrophage and astrocytes. The dissemination of the human rabies virus within an infected host may be mediated by viral escape of the virus from an infected cell and may involve an anti-apoptotic mechanism, which does not kill the neuron or pro-apoptosis of TCD4+ and TCD8+ lymphocytes and which allows for increased proliferation of the virus within the CNS by attenuation of the adaptive immune response. (C) 2011 Elsevier B.V. All rights reserved.

Developing community-based watershed management in Greater Sao Paulo: the case of Santo Andre

This paper describes how watershed protection is being combined with settlement upgrading and land-use management within an area that serves as one of Greater Sao Paulo's main sources of fresh water. This is being undertaken in the municipality of San to Andre. Unlike previous watershed protection measures, which proved ineffective, it recognizes the need to combine the protection of water-sheds with the improvement of conditions in existing settlements and guiding, rather than prohibiting, further settlement. The paper describes how, the community-based watershed management involves the inhabitants of illegal settlements and other stakeholders in an adaptive planning framework that first seeks consensus on what is to be planned before developing the plan, its implementation and its operation, maintenance and monitoring.

The effects of time delays in adaptive phase measurements

It is not possible to make measurements of the phase of an optical mode using linear optics without introducing an extra phase uncertainty. This extra phase variance is quite large for heterodyne measurements, however it is possible to reduce it to the theoretical limit of log (n) over bar (4 (n) over bar (2)) using adaptive measurements. These measurements are quite sensitive to experimental inaccuracies, especially time delays and inefficient detectors. Here it is shown that the minimum introduced phase variance when there is a time delay of tau is tau/(8 (n) over bar). This result is verified numerically, showing that the phase variance introduced approaches this limit for most of the adaptive schemes using the best final phase estimate. The main exception is the adaptive mark II scheme with simplified feedback, which is extremely sensitive to time delays. The extra phase variance due to time delays is considered for the mark I case with simplified feedback, verifying the tau /2 result obtained by Wiseman and Killip both by a more rigorous analytic technique and numerically.

Phase mask selection in wavefront coding systems: an adaptive approach

A method for optimizing the strength of a parametric phase mask for a wavefront coding imaging system is presented. The method is based on an optimization process that minimizes a proposed merit function. The goal is to achieve modulation transfer function invariance while quantitatively maintaining nal image delity. A parametric lter that copes with the noise present in the captured images is used to obtain the nal images, and this lter is optimized. The whole process results in optimum phase mask strength and optimal parameters for the restoration lter. The results for a particular optical system are presented and tested experimentally in the labo- ratory. The experimental results show good agreement with the simulations, indicating that the procedure is useful.

MyD88 Signaling Is Required for Efficient Innate and Adaptive Immune Responses to Paracoccidioides brasiliensis Infection

The mechanisms that govern the initial interaction between Paracoccidioides brasiliensis, a primary dimorphic fungal pathogen, and cells of the innate immunity need to be clarified. Our previous studies showed that Toll-like receptor 2 (TLR2) and TLR4 regulate the initial interaction of fungal cells with macrophages and the pattern of adaptive immunity that further develops. The aim of the present investigation was to assess the role of MyD88, an adaptor molecule used by TLRs to activate genes of the inflammatory response in pulmonary paracoccidioidomycosis. Studies were performed with normal and MyD88(-/-) C57BL/6 mice intratracheally infected with P. brasiliensis yeast cells. MyD88(-/-) macrophages displayed impaired interaction with fungal yeast cells and produced low levels of IL-12, MCP-1, and nitric oxide, thus allowing increased fungal growth. Compared with wild-type (WT) mice, MyD88(-/-) mice developed a more severe infection of the lungs and had marked dissemination of fungal cells to the liver and spleen. MyD88(-/-) mice presented low levels of Th1, Th2, and Th17 cytokines, suppressed lymphoproliferation, and impaired influx of inflammatory cells to the lungs, and this group of cells comprised lower numbers of neutrophils, activated macrophages, and T cells. Nonorganized, coalescent granulomas, which contained high numbers of fungal cells, characterized the severe lesions of MyD88(-/-) mice; the lesions replaced extensive areas of several organs. Therefore, MyD88(-/-) mice were unable to control fungal growth and showed a significantly decreased survival time. In conclusion, our findings demonstrate that MyD88 signaling is important in the activation of fungicidal mechanisms and the induction of protective innate and adaptive immune responses against P. brasiliensis.