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

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.

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Laboratory quantification of a plenoptic wavefront sensor with extended objects

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2269 ◽

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.

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Off-axis point spread function reconstruction from a dual deformable mirror adaptive optics system

10.1117/12.790026 ◽

2008 ◽

Cited By ~ 1

Author(s):

O. Keskin ◽

R. Conan ◽

C. Bradley ◽

C. Blain

Keyword(s):

Adaptive Optics ◽

Point Spread Function ◽

Deformable Mirror ◽

Point Spread ◽

Spread Function ◽

Adaptive Optics System ◽

Function Reconstruction

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A New Design of Large Stroke Micro-Deformable Mirror Actuated by Electrostatic Repulsive Force

2008 Second International Conference on Integration and Commercialization of Micro and Nanosystems ◽

10.1115/micronano2008-70058 ◽

2008 ◽

Cited By ~ 1

Author(s):

Fangrong Hu ◽

Jun Yao ◽

Chuankai Qiu ◽

Dajia Wang

Keyword(s):

Electric Field ◽

Resonant Frequency ◽

Adaptive Optics ◽

Bottom Electrode ◽

Sacrificial Layer ◽

Electrostatic Force ◽

Repulsive Force ◽

Deformable Mirror ◽

Optical Aberrations ◽

Out Of Plane

In this paper, a MEMS mirror actuated by an electrostatic repulsive force has been proposed and analyzed. The mirror consists of four U-shape springs, a fixed bottom electrode and a movable top electrode, there are many comb fingers on the edges of both electrodes. When the voltage is applied to the top and bottom electrodes, an asymmetric electric field is generated to the top movable fingers and springs, thus a net electrostatic force is produced to move the top plate out of plane. This designed micro-mirror is different from conventional MDM based on electrostatic-attractive-force, which is restricted by one-third thickness of the sacrificial layer for the pull-in phenomenon. The characteristic of this MDM has been analyzed, the result shows that the resonant frequency of the first mode is 8 kHz, and the stroke reaches 10μm at 200V, a MDM with large strokes can be realized for the application of adaptive optics in optical aberrations correction.

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Comparison of wavefront sensor models for simulation of adaptive optics

Optics Express ◽

10.1364/oe.17.020575 ◽

2009 ◽

Vol 17 (22) ◽

pp. 20575 ◽

Cited By ~ 1

Author(s):

Zhiwen Wu ◽

Anita Enmark ◽

Mette Owner-Petersen ◽

Torben Andersen

Keyword(s):

Adaptive Optics ◽

Wavefront Sensor ◽

Sensor Models

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

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937033 ◽

2020 ◽

Vol 636 ◽

pp. A88 ◽

Cited By ~ 1

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.

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