High contrast AO test environment


Extreme AO and new light suppressing techniques

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Recapitulation

Goal

The goal of this project is to design and build an optical test environment that can mimic the E-ELT conditions and characterize the influence on the instrument performance by doing representative tests for the systems in EPICS, MICADO and METIS, especially the coronagraphs and phase plates.


Approach
The test-system will consist of a planet and star simulator, which will shine through a simulated Earth atmosphere. This light will be further transported through a system of mirrors and/or lenses, to simulate the telescope itself, before it reaches a deformable mirror. After this mirror the light will be split into two bundles, one for the wave front sensor and one for the "science" that might be guided through a coronograph before it reaches the detector.


Involved Partners
NOVA together with TNO and the Delft Center for Systems and Control.


Progress

Goal
The performance of many E-ELT instruments (like EPICS, MICADO and METIS) depends heavily on the ability of the Adaptive Optics (AO) system to correct for atmospheric turbulences. The increased resolution and contrast requirements also result in increased requirements for the adaptive optics. And in order to test optical components like phase-plates and coronagraphs, it is necessary that there is an optical test bed that can mimic these complicated AO systems.

 

The goal of this project is to design and build such a test environment and to do representative tests for the systems in EPICS, MICADO and METIS, especially the coronagraphs and phase plates. The system will be designed to do tests at optical wavelengths, but the results can immediately be applied to longer wavelengths (like for example METIS). The systems will be designed in such a way that an upgrade to longer wavelengths remains possible.



Approach
The system will exist of a planet and a star simulator, which will shine through an Earth atmosphere simulator. The light will go through a system of mirrors and/or lenses that simulate the telescope after which it falls on a deformable mirror. After this mirror the light will be split in two beams, one for the wave front sensor and a “scientific” beam which could go through a coronagraph before it falls on the detector. Because it is important in this research to verify the influence of a coronagraph or phase-plate on the performance of the whole system, a fast AO system is not required and the calculations to correct for the atmospheric disturbances can be done relatively slowly (typical time for changes in this set-up are in the order of 10Hz, while a real AOO system would work with 1kHz or higher.

 

The work has been distributed in different work packages.

 

WP1: The optical design of the test bed
In collaboration with the Dutch Pis of the different E-ELT instruments and with the aid of optical designers we will make an optical design for the test bed. As much as possible we will choose designs that are commercially available (COTS). The final design will be reviewed by experts.


WP2: MAIT
During the Manufacturing Assembly Integration and Test (MAIT) phase, we will procure the different components and assemble and integrate them into the system. Each module shall first be tested individually before it will be integrated into the system.


WP3: Static and dynamic demonstration of the adaptive optics system.
At the start we will demonstrate that the system can correct for the induced “atmospheric turbulence”. When this is successful we will add to the computer model of the test bed the static aberrations between the wavefront sensor and the scientific detector.  Different "Point Spread Function" (PSF) reconstruction algorithms will be tested by the facility.

 

WP4: Investigate the effects of apodized phase plates on the astrometric capabilities of MICADO
MICADO will make diffraction limited images, however in crowded fields it cannot be excluded that the Point Spread Function (PSF) of bright background sources disturb the image of weak objects. This will limit the possibilities for astrometry and other high contrast high resolution applications.

Certain types of Apodized Phase Plates (APPs) might provide a solution for this problem. They can suppress the background due to the telescope PSF significantly. This will decrease the brightness and therefore the sensitivity of the instrument, but due to the strongly increased contrast this can still be a very useful solution. When designing the test bed, we make sure that the APPs can be tested

 

WP5: Coronagraph and Polarimetry measurements
The coronagraphic module will be used to design and test different coronapgraphs for both EPICS as well as METIS. Both the static as well as the dynamic performance will be compared. Based on this information, design choices to improve our instrument performance will be made for the two instruments mentioned earlier.



Status

A PhD –student  started in September 2011 . Based on the tests that have been done up to now, already significantly improved APPs could be designed.

vapp_tiled

The point spread function of the vAPP at three different wavelengths, showing the achromatic behaviour.


psf_1e-4

Simulation of a new concept for the vAPP coronograph. The two Point Spread Functions are split by the coronograph itself, allowing to reduce the number of optical elements from 3 to 1.

Involved Partners
The work is performed by NOVA, and is further supported by TNO and Delft Center for Systems and Control


Publications

Performance characterization of a broadband vector Apodizing Phase Plate coronagraph
Gilles P.P.L. Otten, Frans Snik, Matthew A. Kenworthy, Matthew N. Miskiewicz and Michael J. Escuti
2014, Optics Express, 22, 24, 30287
http://www.opticsinfobase.org/oe/fulltext.cfm?uri=oe-22-24-30287&id=305355

Vector Apodizing Phase Plate coronagraph: prototyping, characterization and outlook
Gilles P.P.L. Otten, Frans Snik, Matthew A. Kenworthy, Matthew N. Miskiewicz, Michael J. Escuti and Johanan L. Codona
2014, SPIE, 9151, 91511R
http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1915147


Focal-plane wavefront sensing with high-order adaptive optics systems
Korkiakoski, V., Keller, C. U., Doelman, N., Kenworthy, M., Otten, G., Verhaegen, M.
2014, SPIE, 9148, 91485D
http://adsabs.harvard.edu/abs/2014SPIE.9148E..5DK

Combining vector-phase coronagraphy with dual-beam polarimetry
Snik, F., Otten, G., Kenworthy, M., Mawet, D., Escuti, M.
2014, SPIE, 9147, 91477U
http://adsabs.harvard.edu/abs/2014SPIE.9147E..7US

Glossarium

COTS
Commercdial Of The Shelf, implying that you can already buy it and no development trajectory is required.


PSF

Point Spread Function, indicates how spread out a pointsource becomes  after passing through several optical elements when it fall on the detector.

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