scholarly journals Calibration of the island effect: Experimental validation of closed-loop focal plane wavefront control on Subaru/SCExAO

2018 ◽  
Vol 610 ◽  
pp. A18 ◽  
Author(s):  
M. N’Diaye ◽  
F. Martinache ◽  
N. Jovanovic ◽  
J. Lozi ◽  
O. Guyon ◽  
...  
Keyword(s):  
Image Quality ◽  
Focal Plane ◽  
Closed Loop ◽  
Near Infrared ◽  
Experimental Tests ◽  
Relative Increase ◽  
Visible Range ◽  
Wavefront Control ◽  
Island Effect ◽  
Plane Wavefront

Context. Island effect (IE) aberrations are induced by differential pistons, tips, and tilts between neighboring pupil segments on ground-based telescopes, which severely limit the observations of circumstellar environments on the recently deployed exoplanet imagers (e.g., VLT/SPHERE, Gemini/GPI, Subaru/SCExAO) during the best observing conditions. Caused by air temperature gradients at the level of the telescope spiders, these aberrations were recently diagnosed with success on VLT/SPHERE, but so far no complete calibration has been performed to overcome this issue. Aims. We propose closed-loop focal plane wavefront control based on the asymmetric Fourier pupil wavefront sensor (APF-WFS) to calibrate these aberrations and improve the image quality of exoplanet high-contrast instruments in the presence of the IE. Methods. Assuming the archetypal four-quadrant aperture geometry in 8 m class telescopes, we describe these aberrations as a sum of the independent modes of piston, tip, and tilt that are distributed in each quadrant of the telescope pupil. We calibrate these modes with the APF-WFS before introducing our wavefront control for closed-loop operation. We perform numerical simulations and then experimental tests on a real system using Subaru/SCExAO to validate our control loop in the laboratory and on-sky. Results. Closed-loop operation with the APF-WFS enables the compensation for the IE in simulations and in the laboratory for the small aberration regime. Based on a calibration in the near infrared, we observe an improvement of the image quality in the visible range on the SCExAO/VAMPIRES module with a relative increase in the image Strehl ratio of 37%. Conclusions. Our first IE calibration paves the way for maximizing the science operations of the current exoplanet imagers. Such an approach and its results prove also very promising in light of the Extremely Large Telescopes (ELTs) and the presence of similar artifacts with their complex aperture geometry.

scholarly journals SCExAO: First Results and On-Sky Performance

2013 ◽  
Vol 8 (S299) ◽  
pp. 34-35 ◽  
Author(s):  
Thayne Currie ◽  
Olivier Guyon ◽  
Frantz Martinache ◽  
Christophe Clergeon ◽  
Michael McElwain ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Focal Plane ◽  
Closed Loop ◽  
Giant Planets ◽  
Wavefront Sensor ◽  
Strehl Ratio ◽  
Wavefront Control ◽  
Contrast Gain ◽  
First Results ◽  
Plane Wavefront

AbstractWe present new on-sky results for the Subaru Coronagraphic Extreme Adaptive Optics imager (SCExAO) verifying and quantifying the contrast gain enabled by key components: the closed-loop coronagraphic low-order wavefront sensor (CLOWFS) and focal plane wavefront control (“speckle nulling”). SCExAO will soon be coupled with a high-order, Pyramid wavefront sensor which will yield > 90% Strehl ratio and enable 106–107 contrast at small angular separations allowing us to image gas giant planets at solar system scales. Upcoming instruments like VAMPIRES, FIRST, and CHARIS will expand SCExAO's science capabilities.

scholarly journals Measurements of Speckle Lifetimes in Near-infrared Extreme Adaptive Optics Images for Optimizing Focal Plane Wavefront Control

2018 ◽  
Vol 130 (992) ◽  
pp. 104502 ◽  
Author(s):  
Sean B. Goebel ◽  
Olivier Guyon ◽  
Donald N. B. Hall ◽  
Nemanja Jovanovic ◽  
Julien Lozi ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Focal Plane ◽  
Near Infrared ◽  
Wavefront Control ◽  
Plane Wavefront

scholarly journals Closed-loop focal plane wavefront control with the SCExAO instrument

2016 ◽  
Vol 593 ◽  
pp. A33 ◽  
Author(s):  
Frantz Martinache ◽  
Nemanja Jovanovic ◽  
Olivier Guyon
Keyword(s):  
Focal Plane ◽  
Closed Loop ◽  
Wavefront Control ◽  
Plane Wavefront

scholarly journals On-sky verification of Fast and Furious focal-plane wavefront sensing: Moving forward toward controlling the island effect at Subaru/SCExAO

2020 ◽  
Vol 639 ◽  
pp. A52 ◽  
Author(s):  
S. P. Bos ◽  
S. Vievard ◽  
M. J. Wilby ◽  
F. Snik ◽  
J. Lozi ◽  
...  
Keyword(s):  
Focal Plane ◽  
Wavefront Sensing ◽  
Internal Source ◽  
Strehl Ratio ◽  
Atmospheric Conditions ◽  
Severe Problem ◽  
Island Effect ◽  
Wide Range ◽  
Plane Wavefront ◽  
Phase Screens

Context. High-contrast imaging (HCI) observations of exoplanets can be limited by the island effect (IE). The IE occurs when the main wavefront sensor (WFS) cannot measure sharp phase discontinuities across the telescope’s secondary mirror support structures (also known as spiders). On the current generation of telescopes, the IE becomes a severe problem when the ground wind speed is below a few meters per second. During these conditions, the air that is in close contact with the spiders cools down and is not blown away. This can create a sharp optical path length difference between light passing on opposite sides of the spiders. Such an IE aberration is not measured by the WFS and is therefore left uncorrected. This is referred to as the low-wind effect (LWE). The LWE severely distorts the point spread function (PSF), significantly lowering the Strehl ratio and degrading the contrast. Aims. In this article, we aim to show that the focal-plane wavefront sensing (FPWFS) algorithm, Fast and Furious (F&F), can be used to measure and correct the IE/LWE. The F&F algorithm is a sequential phase diversity algorithm and a software-only solution to FPWFS that only requires access to images of non-coronagraphic PSFs and control of the deformable mirror. Methods. We deployed the algorithm on the SCExAO HCI instrument at the Subaru Telescope using the internal near-infrared camera in H-band. We tested with the internal source to verify that F&F can correct a wide variety of LWE phase screens. Subsequently, F&F was deployed on-sky to test its performance with the full end-to-end system and atmospheric turbulence. The performance of the algorithm was evaluated by two metrics based on the PSF quality: (1) the Strehl ratio approximation (SRA), and (2) variance of the normalized first Airy ring (VAR). The VAR measures the distortion of the first Airy ring, and is used to quantify PSF improvements that do not or barely affect the PSF core (e.g., during challenging atmospheric conditions). Results. The internal source results show that F&F can correct a wide range of LWE phase screens. Random LWE phase screens with a peak-to-valley wavefront error between 0.4 μm and 2 μm were all corrected to a SRA > 90% and an VAR  ⪅  0.05. Furthermore, the on-sky results show that F&F is able to improve the PSF quality during very challenging atmospheric conditions (1.3–1.4″seeing at 500 nm). Closed-loop tests show that F&F is able to improve the VAR from 0.27–0.03 and therefore significantly improve the symmetry of the PSF. Simultaneous observations of the PSF in the optical (λ = 750 nm, Δλ = 50 nm) show that during these tests we were correcting aberrations common to the optical and NIR paths within SCExAO. We could not conclusively determine if we were correcting the LWE and/or (quasi-)static aberrations upstream of SCExAO. Conclusions. The F&F algorithm is a promising focal-plane wavefront sensing technique that has now been successfully tested on-sky. Going forward, the algorithm is suitable for incorporation into observing modes, which will enable PSFs of higher quality and stability during science observations.

scholarly journals Focal-plane wavefront sensing with the vector-Apodizing Phase Plate

2019 ◽  
Vol 632 ◽  
pp. A48 ◽  
Author(s):  
S. P. Bos ◽  
D. S. Doelman ◽  
J. Lozi ◽  
O. Guyon ◽  
C. U. Keller ◽  
...  
Keyword(s):  
Focal Plane ◽  
Closed Loop ◽  
Phase Plate ◽  
Wavefront Sensing ◽  
Internal Source ◽  
Maximum Throughput ◽  
Loop Correction ◽  
Common Path ◽  
Plane Wavefront ◽  
Zernike Modes

Context. One of the key limitations of the direct imaging of exoplanets at small angular separations are quasi-static speckles that originate from evolving non-common path aberrations (NCPA) in the optical train downstream of the instrument’s main wavefront sensor split-off. Aims. In this article we show that the vector-Apodizing Phase Plate (vAPP) coronagraph can be designed such that the coronagraphic point spread functions (PSFs) can act as wavefront sensors to measure and correct the (quasi-)static aberrations without dedicated wavefront sensing holograms or modulation by the deformable mirror. The absolute wavefront retrieval is performed with a non-linear algorithm. Methods. The focal-plane wavefront sensing (FPWFS) performance of the vAPP and the algorithm are evaluated via numerical simulations to test various photon and read noise levels, the sensitivity to the 100 lowest Zernike modes, and the maximum wavefront error (WFE) that can be accurately estimated in one iteration. We apply these methods to the vAPP within SCExAO, first with the internal source and subsequently on-sky. Results. In idealized simulations we show that for 107 photons the root mean square (rms) WFE can be reduced to ∼λ/1000, which is 1 nm rms in the context of the SCExAO system. We find that the maximum WFE that can be corrected in one iteration is ∼λ/8 rms or ∼200 nm rms (SCExAO). Furthermore, we demonstrate the SCExAO vAPP capabilities by measuring and controlling the 30 lowest Zernike modes with the internal source and on-sky. On-sky, we report a raw contrast improvement of a factor ∼2 between 2 and 4 λ/D after five iterations of closed-loop correction. When artificially introducing 150 nm rms WFE, the algorithm corrects it within five iterations of closed-loop operation. Conclusions. FPWFS with the vAPP coronagraphic PSFs is a powerful technique since it integrates coronagraphy and wavefront sensing, eliminating the need for additional probes and thus resulting in a 100% science duty cycle and maximum throughput for the target.

scholarly journals Broadband focal plane wavefront control of amplitude and phase aberrations

2012 ◽  
Author(s):  
Tyler D. Groff ◽  
N. Jeremy Kasdin ◽  
Alexis Carlotti ◽  
A. J. Eldorado Riggs
Keyword(s):  
Focal Plane ◽  
Wavefront Control ◽  
Plane Wavefront ◽  
Phase Aberrations

scholarly journals Comparing focal plane wavefront control techniques: Numerical simulations and laboratory experiments

2020 ◽  
Vol 635 ◽  
pp. A192 ◽  
Author(s):  
A. Potier ◽  
P. Baudoz ◽  
R. Galicher ◽  
G. Singh ◽  
A. Boccaletti
Keyword(s):  
Numerical Simulations ◽  
Focal Plane ◽  
Spectral Band ◽  
Wavefront Sensing ◽  
High Contrast ◽  
Contrast Imaging ◽  
Wavefront Control ◽  
Control Techniques ◽  
High Contrast Imaging ◽  
Plane Wavefront

Context. Fewer than 1% of all exoplanets detected to date have been characterized on the basis of spectroscopic observations of their atmosphere. Unlike indirect methods, high-contrast imaging offers access to atmospheric signatures by separating the light of a faint off-axis source from that of its parent star. Forthcoming space facilities, such as WFIRST/LUVOIR/HabEX, are expected to use coronagraphic instruments capable of imaging and spectroscopy in order to understand the physical properties of remote worlds. The primary technological challenge that drives the design of these instruments involves the precision control of wavefront phase and amplitude errors. To suppress the stellar intensity to acceptable levels, it is necessary to reduce phase aberrations to less than several picometers across the pupil of the telescope. Aims. Several focal plane wavefront sensing and control techniques have been proposed and demonstrated in laboratory to achieve the required accuracy. However, these techniques have never been tested and compared under the same laboratory conditions. This paper compares two of these techniques in a closed loop in visible light: the pair-wise (PW) associated with electric field conjugation (EFC) and self-coherent camera (SCC). Methods. We first ran numerical simulations to optimize PW wavefront sensing and to predict the performance of a coronagraphic instrument with PW associated to EFC wavefront control, assuming modeling errors for both PW and EFC. Then we implemented the techniques on a laboratory testbed. We introduced known aberrations into the system and compared the wavefront sensing using both PW and SCC. The speckle intensity in the coronagraphic image was then minimized using PW+EFC and SCC independently. Results. We demonstrate that both techniques – SCC, based on spatial modulation of the speckle intensity using an empirical model of the instrument, and PW, based on temporal modulation using a synthetic model – can estimate the wavefront errors with the same precision. We also demonstrate that both SCC and PW+EFC can generate a dark hole in space-like conditions in a few iterations. Both techniques reach the current limitation of our laboratory bench and provide coronagraphic contrast levels of ∼5 × 10−9 in a narrow spectral band (< 0.25% bandwidth). Conclusions. Our results indicate that both techniques are mature enough to be implemented in future space telescopes equipped with deformable mirrors for high-contrast imaging of exoplanets.

Optical Design of COLIBRÍ: A Fast Follow-up Telescope for Transient Events

2020 ◽  
Vol 09 (01) ◽  
pp. 2050001 ◽  
Author(s):  
J. Fuentes-Fernández ◽  
A. M. Watson ◽  
S. Cuevas ◽  
S. Basa ◽  
J. Floriot ◽  
...  
Keyword(s):  
Image Quality ◽  
Ambient Temperature ◽  
Focal Plane ◽  
Near Infrared ◽  
Optical Design ◽  
Field Of View ◽  
The Future ◽  
Transient Events

COLIBRÍ will be a Franco-Mexican 1.3-m telescope and imager for observing the visible and near infrared counterparts of transient events detected by the future SVOM mission. The imager is divided into two instruments: DDRAGO, with two 4k[Formula: see text][Formula: see text][Formula: see text]4k CCDs observing in [Formula: see text] and [Formula: see text], respectively, and CAGIRE, with one 2k[Formula: see text][Formula: see text][Formula: see text]2k LYNRED or H2RG detector observing in [Formula: see text]. DDRAGO will directly image the telescope focal plane with a field of view (FoV) of 26[Formula: see text][Formula: see text][Formula: see text]26 arcmin. CAGIRE will reimage the focal plane to make a pupil image available for a cold stop and adjust the plate scale to deliver a similar FoV. CAGIRE will not use a conventional collimator-camera configuration but rather an arrangement of lenses that sends the pupil image close to the focal plane after all of the reimaging optics. This allows most of the optics, including the infrared filters, to be at ambient temperature and avoids the complexity of having mechanisms and powered optics within the cryostat (CR). We present here the optical design of the system and a thorough analysis on the expected image quality of the instruments and the telescope.

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