scholarly journals DO-CRIME: Dynamic On-sky Covariance Random Interaction Matrix Evaluation, a novel method for calibrating adaptive optics systems

2020 ◽  
Author(s):  
Olivier Lai ◽  
Mark Chun ◽  
Ryan Dungee ◽  
Jessica Lu ◽  
Marcel Carbillet
Keyword(s):  
Adaptive Optics ◽  
Calibration Procedure ◽  
Wavefront Sensor ◽  
Interaction Matrix ◽  
Wide Field ◽  
Secondary Mirror ◽  
Novel Method ◽  
Measurement Vector ◽  
Random Patterns ◽  
Interaction Matrices

Abstract Adaptive optics systems require a calibration procedure to operate, whether in closed loop or even more importantly in forward control. This calibration usually takes the form of an interaction matrix and is a measure of the response on the wavefront sensor to wavefront corrector stimulus. If this matrix is sufficiently well conditioned, it can be inverted to produce a control matrix, which allows to compute the optimal commands to apply to the wavefront corrector for a given wavefront sensor measurement vector. Interaction matrices are usually measured by means of an artificial source at the entrance focus of the adaptive optics system; however, adaptive secondary mirrors on Cassegrain telescopes offer no such focus and the measurement of their interaction matrices becomes more challenging and needs to be done on-sky using a natural star. The most common method is to generate a theoretical or simulated interaction matrix and adjust it parametrically (for example, decenter, magnification, rotation) using on-sky measurements. We propose a novel method of measuring on-sky interaction matrices ab initio from the telemetry stream of the AO system using random patterns on the deformable mirror with diagonal commands covariance matrices. The approach, being developed for the adaptive secondary mirror upgrade for the imaka wide-field AO system on the UH2.2m telescope project, is shown to work on-sky using the current imaka testbed.

scholarly journals On-sky correction of non-common path aberration with the pyramid wavefront sensor

2020 ◽  
Vol 636 ◽  
pp. A88 ◽  
Author(s):  
S. Esposito ◽  
A. Puglisi ◽  
E. Pinna ◽  
G. Agapito ◽  
F. Quirós-Pacheco ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Critical Issue ◽  
Wavefront Sensor ◽  
Interaction Matrix ◽  
Scientific Instrument ◽  
Wavefront Sensors ◽  
Successful Operation ◽  
Optical Elements ◽  
Common Path ◽  
External Conditions

The paper deals with with the on-sky performance of the pyramid wavefront sensor-based Adaptive Optics (AO) systems. These wavefront sensors are of great importance, being used in all first light AO systems of the ELTs (E-ELT, GMT, and TMT), currently in design phase. In particular, non-common path aberrations (NCPAs) are a critical issue encountered when using an AO system to produce corrected images in an associated astronomical instrument. The AO wavefront sensor (WFS) and the supported scientific instrument typically use a series of different optical elements, thus experiencing different aberrations. The usual way to correct for such NCPAs is to introduce a static offset in the WFS signals. In this way, when the AO loop is closed the sensor offsets are zeroed and the deformable mirror converges to the shape required to null the NCPA. The method assumes that the WFS operation is linear and completely described by some pre-calibrated interaction matrix. This is not the case for some frequently used wavefront sensors like the Pyramid sensor or a quad-cell Shack-Hartmann sensor. Here we present a method to work in closed-loop with a pyramid wavefront sensor, or more generally a non-linear WFS, introducing a wavefront offset that remains stable when AO correction quality changes due to variations in external conditions like star brightness, seeing, and wind speed. The paper details the methods with analytical and numerical considerations. Then we present results of tests executed at the LBT telescope, in daytime and on sky, using the FLAO system and LUCI2 facility instrument. The on-sky results clearly show the successful operation of the method that completely nulls NCPA, recovering diffraction-limited images with about 70% Strehl ratio in H band in variable seeing conditions. The proposed method is suitable for application to the above-mentioned ELT AO systems.

Adaptive optics wide-field microscope corrections using a MEMS DM and Shack-Hartmann wavefront sensor

2011 ◽  
Author(s):  
Oscar Azucena ◽  
Xiaodong Tao ◽  
Justin Crest ◽  
Shaila Kotadia ◽  
William Sullivan ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Wavefront Sensor ◽  
Wide Field

Laboratory quantification of a plenoptic wavefront sensor with extended objects

2020 ◽  
Vol 497 (4) ◽  
pp. 4580-4586
Author(s):  
Zhentao Zhang ◽  
Nazim Bharmal ◽  
Tim Morris ◽  
Yonghui Liang
Keyword(s):  
Adaptive Optics ◽  
Closed Loop ◽  
Optical Design ◽  
Wavefront Sensor ◽  
Wavefront Sensing ◽  
Wide Field ◽  
Loop Correction ◽  
Wavefront Correction ◽  
Set Up ◽  
Experimental Bench

ABSTRACT Adaptive optics (AO) is widely used in ground-based telescopes to compensate the effects of atmosphere distortion, and the wavefront sensor is a significant component in the AO systems. The plenoptic wavefront sensor has been proposed as an alternative wavefront sensor adequate for extended objects and wide field of views. In this paper, a experimental bench has been set up to investigate the slope measurement accuracy and closed-loop wavefront correction performance for extended objects. From the experimental results, it has been confirmed that plenoptic wavefront sensor is suitable for extended objects wavefront sensing with proper optical design. The slope measurements have a good linearity and accuracy when observing extended objects. The image quality is significantly improved after closed-loop correction. A method of global tip/tilt measurement using only plenoptic wavefront sensor frame is proposed in this paper, it is also a potential advantage of plenoptic wavefront sensor in extended objects wavefront sensing.

scholarly journals Experience with wavefront sensor and deformable mirror interfaces for wide-field adaptive optics systems

2016 ◽  
Vol 459 (2) ◽  
pp. 1350-1359 ◽  
Author(s):  
A. G. Basden ◽  
D. Atkinson ◽  
N. A. Bharmal ◽  
U. Bitenc ◽  
M. Brangier ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Wavefront Sensor ◽  
Deformable Mirror ◽  
Wide Field

scholarly journals Proposed New AV-Type Test-Bed for Accurate and Reliable Fish-Eye Lens Camera Self-Calibration

Sensors ◽  
2021 ◽  
Vol 21 (8) ◽  
pp. 2776
Author(s):  
Kang Hyeok Choi ◽  
Changjae Kim
Keyword(s):  
Outer Part ◽  
Calibration Procedure ◽  
Geometric Distortion ◽  
Eye Lens ◽  
Wide Field ◽  
Test Bed ◽  
Self Calibration ◽  
Type Test ◽  
Balanced Distribution ◽  
Fish Eye

The fish-eye lens camera has a wide field of view that makes it effective for various applications and sensor systems. However, it incurs strong geometric distortion in the image due to compressive recording of the outer part of the image. Such distortion must be interpreted accurately through a self-calibration procedure. This paper proposes a new type of test-bed (the AV-type test-bed) that can effect a balanced distribution of image points and a low level of correlation between orientation parameters. The effectiveness of the proposed test-bed in the process of camera self-calibration was verified through the analysis of experimental results from both a simulation and real datasets. In the simulation experiments, the self-calibration procedures were performed using the proposed test-bed, four different projection models, and five different datasets. For all of the cases, the Root Mean Square residuals (RMS-residuals) of the experiments were lower than one-half pixel. The real experiments, meanwhile, were carried out using two different cameras and five different datasets. These results showed high levels of calibration accuracy (i.e., lower than the minimum value of RMS-residuals: 0.39 pixels). Based on the above analyses, we were able to verify the effectiveness of the proposed AV-type test-bed in the process of camera self-calibration.

scholarly journals Comparison of wavefront sensor models for simulation of adaptive optics

2009 ◽  
Vol 17 (22) ◽  
pp. 20575 ◽  
Author(s):  
Zhiwen Wu ◽  
Anita Enmark ◽  
Mette Owner-Petersen ◽  
Torben Andersen
Keyword(s):  
Adaptive Optics ◽  
Wavefront Sensor ◽  
Sensor Models

scholarly journals A Novel Coherence Reduction Method in Compressed Sensing for DOA Estimation

2013 ◽  
Vol 2013 ◽  
pp. 1-9
Author(s):  
Jing Liu ◽  
ChongZhao Han ◽  
XiangHua Yao ◽  
Feng Lian
Keyword(s):  
Compressed Sensing ◽  
Phased Array ◽  
Reduction Method ◽  
Doa Estimation ◽  
Estimation Methods ◽  
Sensing Matrix ◽  
Replacement Method ◽  
Precise Estimation ◽  
Novel Method ◽  
Measurement Vector

A novel method named as coherent column replacement method is proposed to reduce the coherence of a partially deterministic sensing matrix, which is comprised of highly coherent columns and random Gaussian columns. The proposed method is to replace the highly coherent columns with random Gaussian columns to obtain a new sensing matrix. The measurement vector is changed accordingly. It is proved that the original sparse signal could be reconstructed well from the newly changed measurement vector based on the new sensing matrix with large probability. This method is then extended to a more practical condition when highly coherent columns and incoherent columns are considered, for example, the direction of arrival (DOA) estimation problem in phased array radar system using compressed sensing. Numerical simulations show that the proposed method succeeds in identifying multiple targets in a sparse radar scene, where the compressed sensing method based on the original sensing matrix fails. The proposed method also obtains more precise estimation of DOA using one snapshot compared with the traditional estimation methods such as Capon, APES, and GLRT, based on hundreds of snapshots.

Calibration strategy of the pyramid wavefront sensor module of ERIS with the VLT deformable secondary mirror

2012 ◽  
Author(s):  
A. Riccardi ◽  
R. Briguglio ◽  
E. Pinna ◽  
G. Agapito ◽  
F. Quiros-Pacheco ◽  
...  
Keyword(s):  
Wavefront Sensor ◽  
Secondary Mirror ◽  
Sensor Module

scholarly journals The effect of vascular diseases on bioimpedance measurements: mathematical modeling

2018 ◽  
Vol 5 (6) ◽  
Author(s):  
Yomna H. Shash ◽  
Mohamed A. A. Eldosoky ◽  
Mohamed T. Elwakad
Keyword(s):  
Mathematical Models ◽  
Vessel Wall ◽  
Vascular Diseases ◽  
Impedance Analysis ◽  
Wide Field ◽  
Vascular Disorders ◽  
Non Invasive ◽  
Novel Method ◽  
Inner Vessel ◽  
Arteries And Veins

Introduction: The non-invasive nature of bioimpedance technique is the reason for the adoption of this technique in the wide field of bio-research. This technique is useful in the analysis of a variety of diseases and has many advantages. Cardiovascular diseases are the most dangerous diseases leading to death in many regions of the world. Vascular diseases are disorders that affect the arteries and veins. Most often, vascular diseases have greater impacts on the blood flow, either by narrowing or blocking the vessel lumen or by weakening the vessel wall. The most common vascular diseases are atherosclerosis, wall swelling (aneurysm), and occlusion. Atherosclerosis is a disease caused by the deposition of plaques on the inner vessel wall, while a mural aneurysm is formed as a result of wall weakness. The main objective of this study was to investigate the effects of vascular diseases on vessel impedance. Furthermore, this study aimed to develop the measurement of vessel abnormalities as a novel method based on the bioimpedance phenomenon. Methods: Mathematical models were presented to describe the impedance of vessels in different vascular cases. In addition, a 3D model of blood vessels was simulated by COMSOL MULTIPHYSICS.5, and the impedance was measured at each vascular condition. Results: The simulation results clarify that the vascular disorders (stenosis, blockage or aneurysm) have significant impact on the vessel impedance, and thus they can be detected by using the bio-impedance analysis. Moreover, using frequencies in KHz range is preferred in detecting vascular diseases since it has the ability to differentiate between the healthy and diseased blood vessel. Finally, the results can be improved by selecting an appropriate electrodes configuration for analysis. Conclusion: From this work, it can be concluded that bioimpedance analysis (BIA) has the ability to detect vascular diseases. Furthermore, the proposed mathematical models are successful at describing different cases of vascular disorders.

A very wide field wavefront sensor for a very narrow field interferometer

2010 ◽  
Author(s):  
V. Viotto ◽  
R. Ragazzoni ◽  
C. Arcidiacono ◽  
M. Bergomi ◽  
A. Brunelli ◽  
...  
Keyword(s):  
Wavefront Sensor ◽  
Wide Field
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