Vincent Garrel

The Subaru Coronagraphic Extreme Adaptive Optics System: Enabling High-Contrast Imaging on Solar-System Scales

The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is a multipurpose high-contrast imaging platform designed for the discovery and detailed characterization of exoplanetary systems and serves as a testbed for high-contrast imaging technologies for ELTs. It is a multi-band instrument which makes use of light from 600 to 2500nm allowing for coronagraphic direct exoplanet imaging of the inner 3 lambda/D from the stellar host. Wavefront sensing and control are key to the operation of SCExAO. A partial correction of low-order modes is provided by Subarus facility adaptive optics system with the final correction, including high-order modes, implemented downstream by a combination of a visible pyramid wavefront sensor and a 2000-element deformable mirror. The well corrected NIR (y-K bands) wavefronts can then be injected into any of the available coronagraphs, including but not limited to the phase induced amplitude apodization and the vector vortex coronagraphs, both of which offer an inner working angle as low as 1 lambda/D. Non-common path, low-order aberrations are sensed with a coronagraphic low-order wavefront sensor in the infrared (IR). Low noise, high frame rate, NIR detectors allow for active speckle nulling and coherent differential imaging, while the HAWAII 2RG detector in the HiCIAO imager and/or the CHARIS integral field spectrograph (from mid 2016) can take deeper exposures and/or perform angular, spectral and polarimetric differential imaging. Science in the visible is provided by two interferometric modules: VAMPIRES and FIRST, which enable sub-diffraction limited imaging in the visible region with polarimetric and spectroscopic capabilities respectively. We describe the instrument in detail and present preliminary results both on-sky and in the laboratory.

Gemini multiconjugate adaptive optics system review – II. Commissioning, operation and overall performance

The Gemini Multi-conjugate Adaptive Optics System - GeMS, a facility instrument mounted on the Gemini South telescope, delivers a uniform, near di↵raction limited images at near infrared wavelengths (0.95 µm - 2.5 µm) over a field of view of 120 00 . GeMS is the first sodium layer based multi laser guide star adaptive optics system used in astronomy. It uses five laser guide stars distributed on a 60 00 square constellation to measure for atmospheric distortions and two deformable mirrors to compensate for it. In this paper, the second devoted to describe the GeMS project, we present the commissioning, overall performance and operational scheme of GeMS. Performance of each sub-system is derived from the commissioning results. The typical image quality, expressed in full with half maximum, Strehl ratios and variations over the field delivered by the system are then described. A discussion of the main contributor to performance limitation is carried-out. Finally, overheads and future system upgrades are described.

Commissioning status of Subaru laser guide star adaptive optics system

The current status of commissioning and recent results in performance of Subaru laser guide star adaptive optics system is presented. After the first light using natural guide stars with limited configuration of the system in October 2006, we concentrated to complete a final configuration for a natural guide star to serve AO188 to an open use observation. On sky test with full configurations using natural guide star started in August 2008, and opened to a public one month later. We continuously achieved around 0.6 to 0.7 of Strehl ratio at K band using a bright guide star around 9th to 10th magnitude in R band. We found an unexpectedly large wavefront error in our laser launching telescope. The modification to fix this large wavefront error was made and we resumed the characterization of a laser guide star in February 2009. Finally we obtained a round-shaped laser guide star, whose image size is about 1.2 to 1.6 arcsec under the typical seeing condition. We are in the final phase of commissioning. A diffraction limited image by our AO system using a laser guide star will be obtained in the end of 2010. An open use observation with laser guide star system will start in the middle of 2011.

Performance of Subaru adaptive optics system AO188

Subaru adaptive optics system (AO188) is an 188-elements curvature sensor adaptive optics system that is operated in both natural and laser guide star modes. AO188 was installed at Nasmyth platform of the Subaru telescope and it has been successfully operating in the natural guide star mode since October 2008. The performance of AO188 in the natural guide star mode has been well verified from on-sky data obtained with the infrared camera and spectrograph (IRCS). Under normal seeing condition, AO188 achieves K-band Strehl ratio between 60% and 70% using R = 9.0 magnitude natural guide stars and it works well with faint guide stars down to R = 16.5 magnitude. We measured the FWHM and Strehl ratio of stellar images in globular clusters and found that the isoplanatic angle is approximately 30 arcsec. In this paper, we describe an overview of the operation procedure for AO188, as well as its performance such as angular resolution, Strehl ration, and sensitivity gain for detecting faint objects.

The Subaru coronagraphic extreme AO (SCExAO) system: wavefront control and detection of exoplanets with coherent light modulation in the focal plane

The Subaru Coronagraphic Extreme-AO (SCExAO) system is designed for high contrast coronagraphic imaging at small angular separations, and is scheduled to see first light on the Subaru Telescope in early 2011. The wavefront control architecture for SCExAO is optimized for scattered light control and calibration at small angular separations, and is described in this paper. Key subsystems for the SCExAO wavefront control architecture have been successfully demonstrated, and we report results from these tests and discuss their role in the SCExAO system. Among these subsystems, a technique which can calibrate and remove static and slow speckles which traditionally limit high contrast detections is discussed. A visible light lab prototype system at Subaru Telescope recently demonstrated speckle halo reduction to 2e-7 contrast within 2 2λ/D, and removal of static coherent speckles to 3e-9 contrast.

Coronagraphic Low-Order Wavefront Sensor: Postprocessing Sensitivity Enhancer for High-Performance Coronagraphs

Detection and characterization of exoplanets by direct imaging requires a coronagraph designed to deliver high-contrast at small angular separation. To achieve this, an accurate control of low-order aberrations, such as pointing and focus errors, is essential to optimize coronagraphic rejection and avoid the possible confusion between exoplanet light and coronagraphic leaks in the science image. Simulations and laboratory prototyping have shown that a coronagraphic low-order wavefront sensor (CLOWFS), using a single defocused image of a reflective focal-plane ring, can be used to control tip-tilt to an accuracy of 10-3 λ/D. This article demonstrates that the data acquired by CLOWFS can also be used in postprocessing to calibrate residual coronagraphic leaks from the science image. Using both the CLOWFS camera and the science camera in the system, we quantify the accuracy of the method and its ability to successfully remove light due to low-order errors from the science image. We also report the implementation and performance of the CLOWFS on the Subaru Coronagraphic Extreme-AO (SCExAO) system and its expected on-sky performance. In the laboratory, with a level of disturbance similar to that encountered in a post-AO beam, CLOWFS postprocessing has achieved speckle calibration to 1/300 of the raw speckle level. This is about 40 times better than could be done with an idealized PSF subtraction that does not rely on CLOWFS.

Wavefront control with the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system

The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system uses advanced coronagraphic technique for high contrast imaging of exoplanets and disks as close as 1 lambda/D from the host star. In addition to unusual optics, achieving high contrast at this small angular separation requires a wavefront sensing and control architecture which is optimized for exquisite control and calibration of low order aberrations. The SCExAO system was thus designed to include the wavefront sensors required for bias-free high sensitivity and high speed wavefront measurements. Information is combined from two infrared wavefront sensors and a fast visible wavefront sensors to drive a single MEMS type deformable mirror mounted on a tip-tilt mount. The wavefront sensing and control architecture is highly integrated with the coronagraph system.

A Highly Efficient Lucky Imaging Algorithm: Image Synthesis Based on Fourier Amplitude Selection

We propose a new algorithm dramatically enhancing the efficiency of the lucky imaging technique for AO-corrected images in the visible range. It is achieved by a selection based on the relative strength of signal for each spatial frequency in the Fourier domain, making a more efficient use of information contained in each frame. Realistic simulations show that our algorithm allows us to reach the diffraction limit in the visible range on an AO-equipped 8 m telescope and enhances the Strehl ratio of an AO long exposure by a factor of up to 4. It outperforms the lucky imaging technique at an equivalent selection ratio. The fraction of selected data in simulation is also boosted from two to eight times for a given Strehl-ratio performance.

The Subaru coronagraphic extreme AO project: progress report

In 2009 our group started the integration of the SCExAO project, a highly flexible, open platform for high contrast imaging at the highest angular resolution, inserted between the coronagraphic imaging camera HiCIAO and the 188-actuator AO system of Subaru. In its first version, SCExAO combines a MEMS-based wavefront control system feeding a high performance PIAA-based coronagraph. It also includes a coronagraphic low-order wavefront sensor, a non-redundant aperture mask and a visible imaging mode, all of them designed to take full advantage of the angular resolution that an 8-meter telescope has to offer. SCExAO is currently undergoing commissioning, and this paper presents the first on-sky results acquired in August 2011, using together Subarus AO system, SCExAO and HiCIAO.

The Subaru coronagraphic extreme AO project: first observations

In 2009 our group started the integration of the SCExAO project, a highly flexible, open platform for high contrast imaging at the highest angular resolution, inserted between the coronagraphic imaging camera HiCIAO and the 188-actuator AO system of Subaru. In its first version, SCExAO combines a MEMS-based wavefront control system feeding a high performance PIAA-based coronagraph. This paper presents some of the images obtained during the first engineering observations conducted with SCExAO in 2011: diffraction limited imaging in the visible as well as PIAA coronagraphy in the near infrared; along with the wavefront control strategies to be tested on sky during the next round of SCExAO observations, scheduled in the Fall 2012.