scholarly journals The minimum of the time-delay wavefront error in Adaptive Optics

2019 ◽  
Author(s):  
Niek Doelman
Keyword(s):  
Refractive Index ◽  
Time Delay ◽  
Adaptive Optics ◽  
Zero Order ◽  
Outer Scale ◽  
Temporal Prediction ◽  
Residual Phase ◽  
Wavefront Error ◽  
Phase Variance ◽  
Prediction Strategy

Abstract An analytical expression is given for the minimum of the time-delay induced wavefront error (also known as the servo-lag error) in Adaptive Optics systems under temporal prediction filtering. The analysis is based on the von Kármán model for the spectral density of refractive index fluctuations and the hypothesis of frozen flow. An optimal, temporal predictor can achieve up to a factor 1.77 more reduction of the wavefront phase variance compared to the zero-order prediction strategy, which is commonly used in Adaptive Optics systems. Alternatively, an optimal predictor can allow for a 1.41 times longer time-delay to arrive at the same residual phase variance. Generally, the performance of the optimal, temporal predictor depends on the very product of time-delay, wind speed and the reciprocal of turbulence outer scale.

scholarly journals Method of Multi-Angle Transmission Radiowave Tomography of Dielectric Objects

2020 ◽  
Vol 10 (9) ◽  
pp. 3270
Author(s):  
Dmitry Sukhanov ◽  
Kseniya Zavyalova
Keyword(s):  
Refractive Index ◽  
Time Delay ◽  
Homogeneous Medium ◽  
Projection Algorithm ◽  
Propagation Time ◽  
Destructive Testing ◽  
Internal Structures ◽  
Diffraction Effects ◽  
Dielectric Objects ◽  
Non Destructive

A method for solving the inverse problem for reconstructing the spatial distribution of dielectric permittivity from the results of multi-angle transmission broadband radiosounding is proposed. The method is based on inverse wave propagation. The average refractive index of the medium along the wave trajectory is calculated by comparing the results of the calculation of the time delay of the inverse signal in the entire sounding region and the forward propagation time in a homogeneous medium. This method takes into account diffraction effects in solving a direct problem, which allows one to obtain a resolution in the order of a wavelength. The combination of time delays obtained at different probing angles allows the restoration of the distribution of the refractive index in the medium. The paper presents the results of the numerical simulation of this method. The novelty of the proposed approach compared to the conventional back-projection algorithm is that ray approximation is not applied. Instead of the absorption coefficient (used in X-ray tomography), a time delay is considered, which is restored in the entire probed region. The developed method can be widely used in radiowave tomography or microwave tomography for remote non-destructive testing, diagnostics for the internal structures of inhomogeneous media and the restoration of the shapes of opaque objects based on multisensor sensing.

scholarly journals Prediction-Based Control for Nonlinear Systems with Input Delay

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
I. Estrada-Sánchez ◽  
M. Velasco-Villa ◽  
H. Rodríguez-Cortés
Keyword(s):  
Time Delay ◽  
Nonlinear Systems ◽  
Input Signal ◽  
Lyapunov Functional ◽  
The State ◽  
Constant Time Delay ◽  
Change Of Variable ◽  
Lipschitz Systems ◽  
Suitable Change ◽  
Prediction Strategy

This work has two primary objectives. First, it presents a state prediction strategy for a class of nonlinear Lipschitz systems subject to constant time delay in the input signal. As a result of a suitable change of variable, the state predictor asymptotically provides the value of the state τ units of time ahead. Second, it proposes a solution to the stabilization and trajectory tracking problems for the considered class of systems using predicted states. The predictor-controller convergence is proved by considering a complete Lyapunov functional. The proposed predictor-based controller strategy is evaluated using numerical simulations.

Use Of Adaptive Optics Element For Wavefront Error Correction In The Gemini CO2 Laser Fusion System

1980 ◽  
Author(s):  
V. K. Viswanathan ◽  
J. V. Parker ◽  
T. A. Nussmier ◽  
C. J. Swigert ◽  
W. King ◽  
...  
Keyword(s):  
Error Correction ◽  
Adaptive Optics ◽  
Laser Fusion ◽  
Fusion System ◽  
Wavefront Error

scholarly journals COSMOGRAIL

2018 ◽  
Vol 616 ◽  
pp. A183 ◽  
Author(s):  
V. Bonvin ◽  
J. H. H. Chan ◽  
M. Millon ◽  
K. Rojas ◽  
F. Courbin ◽  
...  
Keyword(s):  
Time Delay ◽  
Adaptive Optics ◽  
Signal To Noise Ratio ◽  
Companion Paper ◽  
Data Sets ◽  
Cosmological Constraints ◽  
La Palma ◽  
The Individual ◽  
Precise Time ◽  
Good Agreement

We present time-delay estimates for the quadruply imaged quasar PG 1115+080. Our results are based on almost daily observations for seven months at the ESO MPIA 2.2 m telescope at La Silla Observatory, reaching a signal-to-noise ratio of about 1000 per quasar image. In addition, we re-analyze existing light curves from the literature that we complete with an additional three seasons of monitoring with the Mercator telescope at La Palma Observatory. When exploring the possible source of bias we considered the so-called microlensing time delay, a potential source of systematic error so far never directly accounted for in previous time-delay publications. In 15 yr of data on PG 1115+080, we find no strong evidence of microlensing time delay. Therefore not accounting for this effect, our time-delay estimates on the individual data sets are in good agreement with each other and with the literature. Combining the data sets, we obtain the most precise time-delay estimates to date on PG 1115+080, with Δt(AB) = 8.3+1.5−1.6 days (18.7% precision), Δt(AC) = 9.9+1.1−1.1 days (11.1%) and Δt(BC) = 18.8+1.6−1.6 days (8.5%). Turning these time delays into cosmological constraints is done in a companion paper that makes use of ground-based Adaptive Optics (AO) with the Keck telescope.

Tomographic wavefront error estimation and measurement for Raven, a multi-object adaptive optics demonstrator

2012 ◽  
Author(s):  
Kate Jackson ◽  
Carlos Correia ◽  
Olivier Lardière ◽  
David Andersen ◽  
Colin Bradley
Keyword(s):  
Error Estimation ◽  
Adaptive Optics ◽  
Wavefront Error

Closer to the Theoretical Limit: Spherical Corrections to Aplanatic Solid Immersion Imaging with Adaptive Optics

2012 ◽  
Author(s):  
Y. Lu ◽  
E. Ramsay ◽  
C.R. Stockbridge ◽  
A. Yurt ◽  
F. H. Köklü ◽  
...  
Keyword(s):  
Refractive Index ◽  
Adaptive Optics ◽  
Spherical Aberration ◽  
Deformable Mirror ◽  
Substrate Thickness ◽  
Spot Intensity ◽  
Theoretical Limit ◽  
Thickness Tolerance ◽  
Theory And Experiment ◽  
Good Agreement

Abstract Aplanatic solid immersion lens (SIL) microscopy is required to achieve the highest possible resolution for next generation silicon IC backside inspection and failure analysis. However, aplanatic SILs are susceptible to spherical aberration introduced by substrate thickness mismatch. We have developed a wavefront precompensation technique using a MEMS deformable mirror and demonstrated an increase in substrate thickness tolerance in aplanatic SIL imaging. Good agreement between theory and experiment is achieved and spot intensity increases by at least a factor of two to three are demonstrated for thicknesses deviating several percent from ideal. This technique is also capable of fixing aberrations due to SIL fabrication, off-axis imaging and refractive index mismatch.

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