Jacques Baudrand

Self-coherent camera: first results of a high-contrast imaging bench in visible light

Extreme adaptive optics and coronagraphy are mandatory for direct imaging of exoplanets. Quasi-static aberrations limit the instrument performance producing speckle noise in the focal plane. We propose a Self-Coherent Camera (SCC) to both control a deformable mirror that actively compensates wavefront error, and calibrate the speckle noise. We create a reference beam to spatially modulate the coronagraphic speckle pattern with Fizeau fringes. In a first step, we are able to extract wavefront aberrations from the science image and correct for them using a deformable mirror. In a second step, we apply a post-processing algorithm to discriminate the companion image from the residual speckle field. To validate the instrumental concept, we developed a high contrast imaging bench in visible light. We associated a SCC to a four quadrant phase mask coronagraph and a deformable mirror (DM) with a high number of actuators (32x32 Boston Michromachines MEMS). We will present this bench and show first experimental results of focal plane wavefront sensing and high contrast imaging. The measurements are compared to numerical simulations.

Experimental results of multi-stage four quadrant phase mask coronagraph

In the framework of exoplanet direct imaging, a few coronagraphs have been proposed to overcome the large flux ratio that exists between the star and its planet. However, there are very few solutions that gather in the same time broad band achromaticity, a small inner working angle (shortest angular distance for planet detection), a good throughput for the planet light, and a mature technical feasibility. Here, we propose to use a combination of chromatic Four Quadrant Phase Mask coronagraphs to achromatize the dephasing of this well-studied monochromatic coronagraph. After describing the principle of the technique, we present preliminary results for a compact prototype. Contrast larger than 10000 are reached with more than 250 nm of spectral bandwidth in the visible. Stability over time and effect of the filtering is also discussed.

FUEGOS: multifiber area spectrograph for one Nasmyth focus of the VLT

FUEGOS (Fibre Unit for European General Optical Spectroscopy) is one of the foreseen focal instruments for the future ESO VLT (very large telescope). The goal is to provide the european community with first class equipment allowing high and low resolution spectroscopy for stellar and extragalactic observations in a large field. This large field of view, 30 arcmin provided by the VLT, is quite unique on 8 m class telescopes. The instrument is made of two parts: a fibre positioner attached to the Nasmyth rotator and a spectrograph sitting on the Nasmyth platform. The two assemblies are linked together with optical fibres. The instrument will include two different modes: the MEDUSA mode for the multi-object spectroscopy and the ARGUS mode for the 2D spectroscopy for extended objects. The multi-object positioner is of the robot type, based on a design using two gripper heads travelling simultaneously on a X-Y carriage. It locks magnetically 80 independent optical fibre bundles at object coordinates on a metallic focal surface. 2D spectroscopy is provided through a fibre anamorphoser in three different fields and spatial samplings. The spectrograph is of the white pupil type, based on a catadioptric design with spherical optics throughout. It gives access to spectral resolutions ranging from 1500 to 30000. The detector is a 2048 x 2048 CCD located inside the camera optics.

Theory and laboratory tests of the multi-stage phase mask coronagraph

A large number of coronagraphs have been proposed to overcome the ratio that exists between the star and its planet. The planet finder of the Extremely Large Telescope, which is called EPICS, will certainly need a more efficient coronagraph than the ones that have been developed so far. We propose to use a combination of chromatic Four Quadrant Phase Mask coronagraph to achromatize the dephasing of the device while maintaining a high rejection performance. After describing this multi-stage FQPM coronagraph, we show preliminary results of a study on its capabilities in the framework of the EPICS instrument, the planet finder of the European Extremely Large Telescope. Eventually, we present laboratory tests of a rough prototype of a multi-stage four-quadrant phase mask. On one hand, we deduce from our laboratory data that a detection at the 10-10 level is feasible in monochromatic light. On the other hand, we show the detection of a laboratory companion fainter than 10-8 with a spectral bandwidth larger than 20%.

ISIS IR: The first infrared fibre-fed spectrograph

ISIS IR is the first attempt to use fibre optics for near infrared spectroscopy (λ≤1.8μm). It is a field spectrograph (2D spectroscopy), and can work at various resolving powers (up to 25000). It can be transported anywhere, and soon it will be used at CFHT with one NICMOS 3-based camera.

JWST: A mid-IR coronagraph for imaging extrasolar planets

MIRI, the mid-IR instrument of JWST (JamesWebb Space Telescope), will include a coronagraphic device for which the ultimate goal is the detection and caracterization of extrasolar planets around nearby stars. In this paper, we describe the optical concept of MIRI and the instrumental choices that were made in phase A and B regarding the coronagraphic system. Finally, we will present numerical simulations that we carried out to evaluate the capability for detecting extrasolar giant gazeous planets.

Optical design of the FUEGOS high-resolution multiple fiber spectrograph

This paper describes the feasibility design of a high resolution multiple object fiber spectrograph. High resolution is obtained without cross dispersion with large 305 mm ruled length gratings and the use of the fiber link as an image slicer. The grating has a high groove density to provide a free spectral range larger than the CCD detector. The use of microlenses as focal converter at the slit has several implications on the design of the spectrograph. Unlike single object spectrographs, the presence of a significant telecentric slit field, 6 degrees long, makes the standard parabolic collimator inappropriate. A catadioptric collimator is used instead in double pass to image the intermediary spectrum sideways of the slit. The use of the white pupil and the good image quality of the collimator permit various camera options. The one foreseen is a f/1.25 finite conjugate catadioptric camera with a (2048)224 micrometers pixel detector.

Fiber link for the FUEGOS multiobject spectrograph

FUEGOS (Fibre Unit for European General Optical Spectroscopy) is one of the foreseen focal instrument for the future Europen VLT (Very Large Telescope). It is a multi-object spectrograph widely opened to stellar and extra-galactic programs. In the general concept of this instrument, the fibre link feeding the spectrograph slit from the telescope Nasmyth focus plays a major part. In addition to transporting light with maximum efficiency it is also asked to satisfy a set of very different specifications related to the spectrograph characteristics or to the particular conditions met at the VLT Nasmyth focus. We examine here the engineering solutions that were ultimately adopted and present the first results obtained with a fibre link prototype which was integrated with the help of a dedicated home- made instrumentation. More generally through this presentation, it will be demonstrated that fibre cables coupled with microlenses at both extremities could provide a simple and efficient solution for high resolution fibre fed spectrographs when it is possible to make use of the advantageous plate scale factor of large aperture telescopes.