The impact of Roland Shack's wavefront sensor on the development of modern active optics

2020 ◽  
Author(s):  
Andrew Rakich
Keyword(s):  
Wavefront Sensor ◽  
Active Optics ◽  
The Impact

The segmented pupil experiment for exoplanet detection. 4. A versatile image-based wavefront sensor for active optics

2020 ◽  
Author(s):  
Patrice Martinez ◽  
Carole Gouvret ◽  
Aurélie Marcotto ◽  
Julien Dejonghe ◽  
Alain Spang ◽  
...  
Keyword(s):  
Wavefront Sensor ◽  
Active Optics

scholarly journals High-Sensitivity X-ray Phase Imaging System Based on a Hartmann Wavefront Sensor

2021 ◽  
Vol 7 (1) ◽  
pp. 3
Author(s):  
Ginevra Begani Provinciali ◽  
Martin Piponnier ◽  
Laura Oudjedi ◽  
Xavier Levecq ◽  
Fabrice Harms ◽  
...  
Keyword(s):  
Imaging System ◽  
High Sensitivity ◽  
Test Sample ◽  
Wavefront Sensor ◽  
Reference Image ◽  
High Angular Resolution ◽  
Phase Imaging ◽  
X Ray ◽  
Laboratory Setup ◽  
The Impact

The Hartman wavefront sensor can be used for X-ray phase imaging with high angular resolution. The Hartmann sensor is able to retrieve both the phase and absorption from a single acquisition. The system calculates the shift in a series of apertures imaged with a detector with respect to their reference positions. In this article, the impact of the reference image on the final image quality is investigated using a laboratory setup. Deflection and absorption images of the same sample are compared using reference images acquired in air and in water. It can be easily coupled with tomographic setups to obtain 3D images of both phase and absorption. Tomographic images of a test sample are shown, where deflection images revealed details that were invisible in absorption. The findings reported in this paper can be used for the improvement of image reconstruction and for expanding the applications of X-ray phase imaging towards materials characterization and medical imaging.

scholarly journals Assessing and mitigating alignment defects of the pyramid wavefront sensor: a translation insensitive control method

2018 ◽  
Vol 619 ◽  
pp. A56 ◽  
Author(s):  
V. Deo ◽  
É. Gendron ◽  
G. Rousset ◽  
F. Vidal ◽  
T. Buey ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Control Method ◽  
Wavefront Sensor ◽  
Sampling Errors ◽  
Gradient Sensing ◽  
Design Factor ◽  
Performance Loss ◽  
Spatial Frequencies ◽  
Plane Wavefront ◽  
The Impact

The pyramid wavefront sensor (PWFS) is the currently preferred design for adaptive optics (AO) systems for extremely large telescopes, as focal plane wavefront sensing bears potential for a large intrinsic sensitivity gain when compared to Shack–Hartmann (SH) sensors. Yet, obtaining a high quality pyramidal prism and a model-consistent assembly remains a critical design factor. We demonstrate that the traditional gradient sensing controller is extremely sensitive to prism shape defects and assembly misalignments. We show that even optimal registration of quadrants on the detector may be insufficient to prevent misalignment induced performance loss through a theoretical analysis of the impact of detection plane quadrants sampling errors and individual translations, which may be induced by a variety of mechanical defects. These misalignments displace wavefront information to terms not included in the conventional gradient-like slopes maps and high spatial frequencies become invisible to the sole X− and Y− axis differences. We introduce expanded space control (ESC) for quad-cell signal by generalizing output measurements of the PWFS and demonstrate its insensitivity to misalignment-induced information loss, therefore dramatically relaxing machining and alignment constraints for PWFS engineering. This work presents the theoretical developments leading to ESC design, along with validating performance and robustness results, both in end-to-end numerical simulations and on a PWFS demonstrator bench at LESIA.

scholarly journals Pyramid wavefront sensor optical gains compensation using a convolutional model

2020 ◽  
Vol 644 ◽  
pp. A6
Author(s):  
V. Chambouleyron ◽  
O. Fauvarque ◽  
P. Janin-Potiron ◽  
C. Correia ◽  
J-F. Sauvage ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Closed Loop ◽  
Theoretical Description ◽  
System Level ◽  
Wavefront Sensor ◽  
Accurate Estimation ◽  
Common Path ◽  
Closed Loop Systems ◽  
Fourier Filtering ◽  
The Impact

Context. Extremely large telescopes are overwhelmingly equipped with pyramid wavefront sensors (PyWFS) over the more widely used Shack–Hartmann wavefront sensor to perform their single-conjugate adaptive optics (SCAO) mode. The PyWFS, a sensor based on Fourier filtering, has proven to be highly successful in many astronomy applications. However, this sensor exhibits non-linear behaviours that lead to a reduction of the sensitivity of the instrument when working with non-zero residual wavefronts. This so-called optical gains (OG) effect, degrades the closed-loop performance of SCAO systems and prevents accurate correction of non-common path aberrations (NCPA). Aims. In this paper, we aim to compute the OG using a fast and agile strategy to control PyWFS measurements in adaptive optics closed-loop systems. Methods. Using a novel theoretical description of PyWFS, which is based on a convolutional model, we are able to analytically predict the behaviour of the PyWFS in closed-loop operation. This model enables us to explore the impact of residual wavefront errors on particular aspects such as sensitivity and associated OG. The proposed method relies on the knowledge of the residual wavefront statistics and enables automatic estimation of the current OG. End-to-end numerical simulations are used to validate our predictions and test the relevance of our approach. Results. We demonstrate, using on non-invasive strategy, that our method provides an accurate estimation of the OG. The model itself only requires adaptive optics telemetry data to derive statistical information on atmospheric turbulence. Furthermore, we show that by only using an estimation of the current Fried parameter r0 and the basic system-level characteristics, OGs can be estimated with an accuracy of less than 10%. Finally, we highlight the importance of OG estimation in the case of NCPA compensation. The proposed method is applied to the PyWFS. However, it remains valid for any wavefront sensor based on Fourier filtering subject from OG variations.

scholarly journals Impact of CMOS Pixel and Electronic Circuitry in the Performance of a Hartmann-Shack Wavefront Sensor

Sensors ◽  
2018 ◽  
Vol 18 (10) ◽  
pp. 3282 ◽  
Author(s):  
Úrsula Abecassis ◽  
Davies de Lima Monteiro ◽  
Luciana Salles ◽  
Carlos de Moraes Cruz ◽  
Pablo Agra Belmonte
Keyword(s):  
Oxide Semiconductor ◽  
Wavefront Sensor ◽  
Cmos Process ◽  
Reconstruction Algorithms ◽  
Circuit Simulator ◽  
Sensor Performance ◽  
Electronic Circuitry ◽  
Reconstruction Methods ◽  
Active Pixel ◽  
The Impact

This work presents a numerical simulation of a Hartmann-Shack wavefront sensor (WFS) that assesses the impact of integrated electronic circuitry on the sensor performance, by evaluating a full detection chain encompassing wavefront sampling, photodetection, electronic circuitry and wavefront reconstruction. This platform links dedicated C algorithms for WFS to a SPICE circuit simulator for integrated electronics. The complete codes can be easily replaced in order to represent different detection or reconstruction methods, while the circuit simulator employs reliable models of either off-the-shelf circuit components or custom integrated circuit modules. The most relevant role of this platform is to enable the evaluation of the applicability and constraints of the focal plane of a given wavefront sensor prior to the actual fabrication of the detector chip. In this paper, we will present the simulation results for a Hartmann-Shack wavefront sensor with an orthogonal array of quad-cells (QC) integrated along with active-pixel (active-pixel sensor (APS)) circuitry and analog-to-digital converters (ADC) on a “complementary metal oxide semiconductor” (CMOS) process and deploying a modal wavefront reconstructor. This extended simulation capability for wavefront sensors enables the test and verification of different photosensitive and circuitry topologies for position-sensitive detectors combined with the simulation of sampling microlenses and reconstruction algorithms, with the goal of enhancing the accuracy in the prediction of the wavefront-sensor performance before a detector CMOS chip is actually fabricated.

Formation of Lunar Craters and Bright Rays as a Result of Meteorite Impacts

1962 ◽  
Vol 14 ◽  
pp. 415-418
Author(s):  
K. P. Stanyukovich ◽  
V. A. Bronshten
Keyword(s):  
Explosive Charge ◽  
The Moon ◽  
Meteorite Impacts ◽  
The Earth ◽  
Lunar Craters ◽  
The Impact

The phenomena accompanying the impact of large meteorites on the surface of the Moon or of the Earth can be examined on the basis of the theory of explosive phenomena if we assume that, instead of an exploding meteorite moving inside the rock, we have an explosive charge (equivalent in energy), situated at a certain distance under the surface.

The Geosciences Applied to Lunar Exploration

1962 ◽  
Vol 14 ◽  
pp. 169-257 ◽  
Author(s):  
J. Green
Keyword(s):  
Lunar Surface ◽  
Probable Mechanism ◽  
Point Of View ◽  
Lunar Exploration ◽  
Geological Model ◽  
Apply Geophysics ◽  
Surface Features ◽  
The Impact

The term geo-sciences has been used here to include the disciplines geology, geophysics and geochemistry. However, in order to apply geophysics and geochemistry effectively one must begin with a geological model. Therefore, the science of geology should be used as the basis for lunar exploration. From an astronomical point of view, a lunar terrain heavily impacted with meteors appears the more reasonable; although from a geological standpoint, volcanism seems the more probable mechanism. A surface liberally marked with volcanic features has been advocated by such geologists as Bülow, Dana, Suess, von Wolff, Shaler, Spurr, and Kuno. In this paper, both the impact and volcanic hypotheses are considered in the application of the geo-sciences to manned lunar exploration. However, more emphasis is placed on the volcanic, or more correctly the defluidization, hypothesis to account for lunar surface features.

Asteroid and Comet Impact Speeds upon Mars: Significance for Panspermia and the Supply of Organics

1997 ◽  
Vol 161 ◽  
pp. 197-201 ◽  
Author(s):  
Duncan Steel
Keyword(s):  
Probability Distributions ◽  
Regions Of Interest ◽  
Significant Fraction ◽  
Organic Chemicals ◽  
Impact Speed ◽  
The Mean ◽  
The Impact

AbstractWhilst lithopanspermia depends upon massive impacts occurring at a speed above some limit, the intact delivery of organic chemicals or other volatiles to a planet requires the impact speed to be below some other limit such that a significant fraction of that material escapes destruction. Thus the two opposite ends of the impact speed distributions are the regions of interest in the bioastronomical context, whereas much modelling work on impacts delivers, or makes use of, only the mean speed. Here the probability distributions of impact speeds upon Mars are calculated for (i) the orbital distribution of known asteroids; and (ii) the expected distribution of near-parabolic cometary orbits. It is found that cometary impacts are far more likely to eject rocks from Mars (over 99 percent of the cometary impacts are at speeds above 20 km/sec, but at most 5 percent of the asteroidal impacts); paradoxically, the objects impacting at speeds low enough to make organic/volatile survival possible (the asteroids) are those which are depleted in such species.

Organic Syntheses During the Impact of a Comet with a Gaseous Planet

1997 ◽  
Vol 161 ◽  
pp. 189-195
Author(s):  
Cesare Guaita ◽  
Roberto Crippa ◽  
Federico Manzini
Keyword(s):  
Polymeric Material ◽  
Molecular Form ◽  
Parent Compound ◽  
Blue Filter ◽  
Organic Syntheses ◽  
The Impact

AbstractA large amount of CO has been detected above many SL9/Jupiter impacts. This gas was never detected before the collision. So, in our opinion, CO was released from a parent compound during the collision. We identify this compound as POM (polyoxymethylene), a formaldehyde (HCHO) polymer that, when suddenly heated, reformes monomeric HCHO. At temperatures higher than 1200°K HCHO cannot exist in molecular form and the most probable result of its decomposition is the formation of CO. At lower temperatures, HCHO can react with NH3 and/or HCN to form high UV-absorbing polymeric material. In our opinion, this kind of material has also to be taken in to account to explain the complex evolution of some SL9 impacts that we observed in CCD images taken with a blue filter.

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