Sensing and control of segmented mirrors with a pyramid wavefront sensor in the presence of spiders

The segmentation of the telescope pupil (by spiders & the segmented M4) create areas of phase isolated by the width of the spiders on the wavefront sensor (WFS), breaking the spatial continuity of the wavefront. The poor sensitivity of the Pyramid WFS (PWFS) to differential piston leads to badly seen and therefore uncontrollable differential pistons. In close loop operation, differential pistons between segments will settle around integer values of the average sensing wavelength. The differential pistons typically range from one to ten times the sensing wavelength and vary rapidly over time, leading to extremely poor performance. In addition, aberrations created by atmospheric turbulence will contain large amounts of differential piston between the segments. Removing piston contribution over each of the DM segments leads to poor performance. In an attempt to reduce the impact of unwanted differential pistons that are injected by the AO correction, we compare three different approaches. We first limit ourselves to only use the information measured by the PWFS, in particular by reducing the modulation. We show that using this information sensibly is important but will not be sufficient. We discuss possible ways of improvement by using prior information. A second approach is based on phase closure of the DM commands and assumes the continuity of the correction wavefront over the entire unsegmented pupil. The last approach is based on the pair-wise slaving of edge actuators and shows the best results. We compare the performance of these methods using realistic end-to-end simulations. We find that pair-wise slaving leads to a small increase of the total wavefront error, only adding between 20-45 nm RMS in quadrature for seeing conditions between 0.45-0.85 arcsec. Finally, we discuss the possibility of combining the different proposed solutions to increase robustness.Comment: 12 pages, 15 figures, AO4ELT5 Proceedings, Adaptive Optics for Extremely Large Telescopes 5, Conference Proceeding, Tenerife, Canary Islands, Spain, June 25-30, 201

SARS-CoV-2 seroprevalence in the urban population of Qatar: An analysis of antibody testing on a sample of 112,941 individuals

ABSTRACTBackgroundQatar has experienced a large SARS-CoV-2 epidemic. Our first objective was to assess the proportion of the urban population that has been infected with SARS-CoV-2, by measuring the prevalence of detectable antibodies. Our second objective was to identify predictors for infection and for having higher antibody titers.MethodsResidual blood specimens from individuals receiving routine and other clinical care between May 12-September 9, 2020 were tested for anti-SARS-CoV-2 antibodies. Associations with seropositivity and higher antibody titers were identified through regression analyses. Probability weights were applied in deriving the epidemiological measures.ResultsWe tested 112,941 individuals (∼10% of Qatar’s urban population), of whom 51.6% were men and 66.0% were 20-49 years of age. Seropositivity was 13.3% (95% CI: 13.1-13.6%) and was significantly associated with sex, age, nationality, clinical-care type, and testing date. The proportion with higher antibody titers varied by age, nationality, clinical-care type, and testing date. There was a strong correlation between higher antibody titers and seroprevalence in each nationality, with a Pearson correlation coefficient of 0.85 (95% CI: 0.47-0.96), suggesting that higher antibody titers may indicate repeated exposure to the virus. The percentage of antibody-positive persons with prior PCR-confirmed diagnosis was 47.1% (95% CI: 46.1-48.2%), severity rate was 3.9% (95% CI: 3.7-4.2%), criticality rate was 1.3% (95% CI: 1.1-1.4%), and fatality rate was 0.3% (95% CI: 0.2-0.3%).ConclusionsFewer than two in every 10 individuals in Qatar’s urban population had detectable antibodies against SARS-CoV-2 between May 12-September 9, 2020, suggesting that this population is still far from the herd immunity threshold and at risk from a subsequent epidemic wave.</jats:sec

Coupling of WFS with a segmented DM “Test of different concepts: SH, Pyramid, Zernike phase sensor”

LAM is developing several R&amp;D activities for E-ELT instrumentation, in particular, different WFS concepts are investigated (Pyramid, ZELDA, a Zernike phase mask sensor, Phase diversity or still NL Curvature) and an ESO-EELT M1 mirror segment (1.5 m) has been demonstrated. Segmented mirrors are not only the solution for the problem of ELTs monolithic size but also for other questions related to fabrication, optics replacement and transport. And, they are widely used today for other applications: fiber coupling, LGS beam shaping, etc. Their only problem is how to assure the cophasing of segments to take advantage of the full optimum size. In the present work, we study the sensitivity to different WFS (Sack-Hartmann, Pyramid and ZELDA) to pupil phase discontinuity using a PTT mirror from Iris AO. Various test such as segment phasing, stability, saturation, flat, or still the addressing mode are then performed and compared

Coupling of WFS with a segmented DM “Test of different concepts: SH, Pyramid, Zernike phase sensor”

LAM is developing several R&amp;D activities for E-ELT instrumentation, in particular, different WFS concepts are investigated (Pyramid, ZELDA, a Zernike phase mask sensor, Phase diversity or still NL Curvature) and an ESO-EELT M1 mirror segment (1.5 m) has been demonstrated. Segmented mirrors are not only the solution for the problem of ELTs monolithic size but also for other questions related to fabrication, optics replacement and transport. And, they are widely used today for other applications: fiber coupling, LGS beam shaping, etc. Their only problem is how to assure the cophasing of segments to take advantage of the full optimum size. In the present work, we study the sensitivity to different WFS (Sack-Hartmann, Pyramid and ZELDA) to pupil phase discontinuity using a PTT mirror from Iris AO. Various test such as segment phasing, stability, saturation, flat, or still the addressing mode are then performed and compared

Proton exchanged waveguides in LiNbO3 and LiTaO3 for integrated lasers and nonlinear frequency converters

We present a review of our research activities concerning the proton exchange technique on lithium niobate and lithium tantalate for integrated lasers and nonlinear frequency converters. In the first part we present the material characterizations that allowed us to establish the phase diagram of the proton exchanged layers on both crystals. In the second part we show how the knowledge of these phase diagrams allows us to understand and handle the problem of the reduction of the excited-state lifetime of the rare-earth ions in Nd- and Er-doped crystals. In the third part, we describe the influence of the different proton exchange processes on the nonlinearity and the domain structure of periodically poled crystals, which leads us to recommend the use of waveguides fabricated using low-acidity melts, which preserves both the nonlinear coefficient and the domain structure. ©1998 Society of Photo-Optical Instrumentation Engineers

Fourier wavefront reconstruction with a pyramid wavefront sensor

International audienceUsing Fourier methods to reconstruct the phase measured by a wavefront sensor (WFS) can significantly re- duce the number of computations required, as well as easily enable predictive reconstruction methods based on knowledge of the adaptive optics system, atmospheric turbulence and wind profile. Previous work on Fourier re- construction has focused on the Shack-Hartmann WFS. With increasing interest in the highly sensitive Pyramid WFS we present the development of Fourier reconstruction tools tailored to the Pyramid sensor. We include the development of the Fourier model, it’s use for formulating error budgets and a laboratory demonstration of Fourier reconstruction with a Pyramid WFS

HARMONI at ELT: a telescope simulator for laser tomographic AO

International audienc

Optimized calibration of the adaptive optics system on the LAM Pyramid bench

International audienceThe Pyramid wave-front sensor (WFS) is currently the baseline for several future adaptive optics (AO) systems, including the first light systems planned for the era of Extremely Large Telescopes (ELTs). Extensive investigation into the Pyramid WFS aim to prepare for this new generation of AO systems, characterizing its behavior under realistic conditions and developing experimental procedures to optimise performance. An AO bench at Laboratoire d'Astrophysique de Marseille has been developed to analyze the behavior of the Pyramid and develop the necessary operational and calibration routines to optimize performance. The test bench comprises a Pyramid WFS, an ALPAO 9 × 9 deformable mirror (DM), a rotating phase screen to simulate atmospheric turbulence and imaging camera. The Pyramid WFS utilizes the low noise OCAM 2 camera to image the four pupils and real time control is realized using the adaptive optics simulation software OOMAO (Object Oriented Matlab Adaptive Optics toolbox). 1 Here we present the latest experimental results from the Pyramid test bench, including comparison with current Pyramid models and AO simulations. We focus on the calibration of the AO system and testing the impact of non-linear effects on the performance of the Pyramid. The results demonstrate good agreement with our current models, in particular with the addition of more realistic elements: non-common path aberrations and the optical quality of the Pyramid prism

Experimental implementation of a Pyramid WFS: Towards the

Investigations into the Pyramid wavefront sensor (P-WFS) have experimentally demonstrated the ability toachieve a better performance than with a standard Shack-Hartmann sensor (SH-WFS). Implementation on theLarge Binocular Telescope (LBT) provided the rst operational demonstration on a facility-class instrument ofa P-WFS on sky. The desire to implement a Pyramid on an Extremely Large Telescope (ELT) requires furthercharacterisation in order to optimise the performance and match our knowledge and understanding of otherwave-front sensors (WFSs).Within the framework of the European Extremely Large Telescope (E-ELT), the Laboratoire d'Astrophysiquede Marseille (LAM) is involved in the preparation of the Single Conjugate Adaptive Optics (SCAO) system ofHARMONI, E-ELT's 1st light integral eld spectrograph (IFU). The current baseline WFS for this adaptiveoptics system is a Pyramid WFS using a high speed and sensitive OCAM2 camera. At LAM we are currentlycarrying out laboratory demonstrations of a Pyramid-WFS, with the aim to fully characterise the behaviour ofthe Pyramid in terms of sensitivity and linear range. This will lead to a full operational procedure for the use ofthe Pyramid on-sky, assisting with current designs and future implementations. The nal goal is to provide anon sky comparison between the Pyramid and Shack-Hartmann at Observatoire de la C^ote d'Azur (OCA). Herewe present our experimental setup and preliminary results