Pascal Puget

High-order adaptive optics requirements for direct detection of extrasolar planets: Application to the SPHERE instrument

The detection of extrasolar planets implies an extremely high-contrast, long-exposure imaging capability at near infrared and probably visible wavelengths. We present here the core of any Planet Finder instrument, that is, the extreme adaptive optics (XAO) subsystem. The level of AO correction directly impacts the exposure time required for planet detection. In addition, the capacity of the AO system to calibrate all the instrument static defects ultimately limits detectivity. Hence, the extreme AO system has to adjust for the perturbations induced by the atmospheric turbulence, as well as for the internal aberrations of the instrument itself. We propose a feasibility study for an extreme AO system in the frame of the SPHERE (Spectro-Polarimetry High-contrast Exoplanet Research) instrument, which is currently under design and should equip one of the four VLT 8-m telescopes in 2010.

Study of the dynamic aberrations of the human tear film

The dynamic aberrations introduced by the human tear film are studied by measuring the topography of the tear film surface on 14 subjects using a curvature sensing setup. The RMS wavefront error variation of the data obtained is presented showing the non-negligible contribution of the tear film to overall eye aberrations. The tear film wavefronts are decomposed in their constituent Zernike terms, showing stronger contributions from 4th order terms and terms with vertical symmetry, and the temporal behaviour of these aberrations is analysed.

Final performance and lesson-learned of SAXO, the VLT-SPHERE extreme AO: from early design to on-sky results

The extreme AO system, SAXO (SPHERE AO for eXoplanet Observation), is the heart of the SPHERE system, feeding the scientific instruments with flat wave front corrected from all the atmospheric turbulence and internal defects. We will present the final performance of SAXO obtained during the instrument AIT in Europe as well as the very first on-sky results. The main requirements and system characteristics will be recalled and the full AO loop performance will be quantified and compared to original specifications. It will be demonstrated that SAXO meets or even exceeds (especially its limit magnitude and its jitter residuals) its challenging requirements (more than 90% of SR in H band and a 3 mas residual jitter). Finally, after 10 years of AO developments, from early design to final on-sky implementations, some critical system aspects as well as some important lesson-learned will be presented in the perspective of the future generation of complex AO systems for VLTs and ELTs.

Curvature sensor for the measurement of the static corneal topography and the dynamic tear film topography in the human eye

A system to measure the topography of the first optical surface of the human eye noninvasively by using a curvature sensor is described. The static corneal topography and the dynamic topography of the tear film can both be measured, and the topographies obtained are presented. The system makes possible the study of the dynamic aberrations introduced by the tear film to determine their contribution to the overall ocular aberrations in healthy eyes, eyes with corneal pathologies, and eyes wearing contact lenses.

The SPHERE IFS at work

SPHERE is an extrasolar planet imager whose goal is to detect giant extrasolar planets in the vicinity of bright stars and to characterize them through spectroscopic and polarimetric observations. It is a complete system with a core made of an extreme-Adaptive Optics (AO) turbulence correction, a pupil tracker and NIR and Visible coronagraph devices. At its back end, a differential dual imaging camera and an integral field spectrograph (IFS) work in the Near Infrared (NIR) (0.95 ≤λ≤2.32 μm) and a high resolution polarization camera covers the visible (0.6 ≤λ≤0.9 μm). The IFS is a low resolution spectrograph (R~50) operates in the near IR (0.95≤λ≤1.6 μm), an ideal wavelength range for the detection of planetary features, over a field of view of about 1.7 x 1.7 square arcsecs. Form spectra it is possible to reconstruct monochromatic images with high contrast (10-7) and high spatial resolution, well inside the star PSF. In this paper we describe the IFS, its calibration and the results of several performance which IFS underwent. Furthermore, using the IFS characteristics we give a forecast on the planetary detection rate.

SPHERE IFS optical concept description and design overview

Integral field spectroscopy coupled with an extreme adaptive optics system and coronagraphy allows a marked improvement of the standard spectroscopic simultaneous differential imaging calibration technique. Hence, with an integral field spectrograph (IFS) direct imaging of extrasolar giant planets becomes potentially feasible over a wide range of ages, masses, and separations from the hosting stars. This aim represents the prime goal of the planet finder instrument for the VLT (SPHERE). Inside SPHERE, the IFS channel exploits various spectral features of the candidate planets in the near infrared, in order to reduce the speckles noise at the level of the stellar background noise, over a field of view comprised between the coronagraphic inner working angle and the outer working angle provided by the SPHERE extreme adaptive optic system (SAXO). The IFS allows then to realize an extensive spectroscopic simultaneous differential imaging calibration technique, and at least in few cases, to get the spectrum of the candidate extrasolar giant planets. Here we present the IFS baseline design, which is based upon a new optical concept we developed for its integral field unit (BIGRE). When applied to the technical specifications of SPHERE IFS, a BIGRE integral field unit is able to take into account all the effects appearing when integral field spectroscopy is used in diffraction limited conditions and for high-contrast imaging purposes. Finally a BIGRE-oriented IFS optical design is shown here to reach the requested high optical quality by standard lenses-based optical devices.

OMEGA IR spectral imager for Mars 96 mission

The goal of the OMEGA instrument (planned to fly the Mars96 Orbiter) is to monitor the past and present evolution of Mars through visible and infrared spectral mapping of its surface. The spectral range (0.5 to 5.1 micrometers) includes signatures of major and minor components of both the surface and the atmosphere of Mars. The spectral and spatial resolutions required and the high signal to noise ratio lead to a three channel instrument: (1) A visible spectrometer (whiskbroom type) with a bidimensional silicon array (288 by 384 elements 23 by 23 micrometers) and a refractive telescope illuminating a holographic grating. (2) A two-channel infrared spectrometer (pushbroom type) based on linear InSb array (128 elements). A reflective telescope and a scanning device give the imaging capability. The IR detectors, cooled at 77 K were developed in France by the Societe Anonyme de Telecommunication (SAT) for this instrument with adapted geometry and specific two band filters. A specific electronic was developed for this instrument, especially one digital electronics based on a transputer associated to a digital signal processor in order to obtain a high efficiency, error free, data compression. After its space qualification, the instrument was fully calibrated at the Institut dAstrophysique Spatiale (IAS) Orsay.

Calibration and data reduction for planet detection with SPHERE-IFS

The 2nd generation VLT instrument SPHERE will include an integral field spectrograph to enhance the capabilities of detection of planetary companions close to bright stars. SPHERE-IFS is foreseen to work in near IR (0.95-1.65 micron) at low spectral resolution. This paper describes the observing strategies, the adopted hardware solutions for calibrating the instrument, and the data reduction procedures that are mandatory for the achievement of the extreme contrast performances for which the instrument is designed.

BIGRE: a new double microlens array for the integral field spectrograph of SPHERE

IFS is the Integral Field Spectrograph for SPHERE, a 2nd generation instrument for VLT devoted to the search of exoplanets. To achieve the performances required for the IFS a new device sampling the focal plane has been designed, prototyped and tested in laboratory. This device named BIGRE consists of a system made of two microlens arrays with different focal lengths and thickness equal to the sum of them and precisely aligned each other. Moreover a mask has been deposited on the first array to produce a field stop for each lenslet. Laboratory tests confirmed that specifications and properties of the prototype are met by state of the art on optics microlens manufacturing. To characterize the device, a simulator of IFS has been built in laboratory and the BIGRE properties have been tested in real working conditions, showing that the design of the double array fulfills IFS requirements.

Camera of the Infrared Space Observatory

The Infrared Space Observatory (ISO) camera (ISOCAM) is designed to map selected regions of the sky in the spectral region from 2.5 to 17 μm at various spatial and spectral resolutions and at high sensitivity (at >4 μm, <1 mJy/10 s in 200 5). It will make images, within the 3-arcmin field of view of the ISO telescope, with two 32 x 32 IR array detectors: an InSb charge injection device (CID) for the 2.5- to 5.5-μm range and a Si:Ga direct voltage readout for the 4- to 17-μm range. Four different pixel fields of view are available on each channel: 1.5, 3, 6, and 12 arcsec. The spectral range can be selected in each channel by a set of about 10 fixed bandpass filters (resolution from 2 to 100) and continuous variable filters (resolution ≈45); polarization measurements are possible as well. A very wide range of astrophysical problems can be tackled with ISOCAM. We present a brief description of the program planned by the ISOCAM team.