This will count as one of your downloads.
You will have access to both the presentation and article (if available).
Development and initial testing of a fiber-fed Fourier transform spectrograph for solar spectroscopy
In this paper, we discuss the advantages of using EvWaCo to observe and characterize exoplanets with a space-based telescope. In the first section, we describe the system and present the current results obtained with the EvWaCo testbed. We also illustrate the capability of this coronagraph to detect the companion 30,000 times (respectively, 100,000 times) fainter than the central star at distances equal to 15 Airy radii (respectively, 30 Airy radii) from the PSF center in polychromatic and unpolarized light.
In the second section, we describe the design of the prototype dedicated to the on-sky tests of the instrument with the 2.4 m Thai National Telescope at horizon 2020. This prototype has been designed with the objective to reach a contrast equal to a few 10-4 at the inner working angle (IWA) equal to 3 λ/D from the star PSF center while observing through the atmosphere over the full photometric I-band. This prototype will include an adaptive optics specified to reach at λ ≈ 800 nm a Strehl ratio > 0.8 for magnitude m < 7.
In the third section, we show the theoretical performance of EvWaCo: a contrast comprised between a few 10-6 and 10-7 in the I-Band between 3 λ/D and 10 λ/D in the I-Band for an IWA equal to 3 λ/D with a Gaussian apodization in unpolarized light. We also show that similar contrasts performance are obtained in the V-, R-, bands, thus illustrating the EvWaCo quasi-achromaticity. Finally, we discuss the advantages and the limitation using the proposed concept for space-based observations and spectral characterization of exoplanets.
The EvWaCo concept has been demonstrated and this instrument is achromatic over the I-band of the Johnson- Cousins photometric system in unpolarized light. We have measured over this photometric band an Inner Working Angle (IWA) equal to 6 λ/D and contrasts of a few 10-6 at distances greater than 10 Airy radii from the star Point Spread Function (PSF) center.
This paper describes the continuation of the project, from this setup of demonstration to the first prototype operating on the sky at horizon 2020. The objective is to show the capability of the full system to provide IWA and raw contrasts close to the state-of-art performance with the Thai National Telescope, by observing through an unobstructed elliptical pupil of major axis length equal to 1 m. The system will demonstrate over the full I-band an IWA close to 3 λ/D and raw contrasts equal to a few 10-4 at a distance equal to the IWA from the PSF.
The current projects include: i) the development of a focal reducer for the 2.3 m Thai National Telescope (TNT), ii) the development of the Evanescent Wave Coronagraph dedicated to the high contrast observations of star close environment and iii) the development of low resolution spectrographs for the Thai National Telescope and for the 0.7 m telescopes of NARIT regional observatories. In each project, our activities start from the instrument optical and mechanical design to the simulation of the performance, the development of the prototype and finally to the final system integration, alignment and tests. Most of the mechanical parts are manufactured by using the facilities of NARIT precision mechanical workshop that includes a 3-axis Computer Numerical Control (CNC) to machine the mechanical structures and a Coordinate Measuring Machine (CMM) to verify the dimensions.
In this paper, we give an overview of the optical laboratory activities and of the associated facilities. We also describe the objective of the current projects, present the specifications and the design of the instruments and establish the status of development and we present our future plans.
During a phase-0 study performed in 2005 at CNES, ONERA and in the laboratories, the critical subsystems of the optical payload have been investigated and a preliminary system integration has been performed. These subsystems are mostly the broadband (2.5-5 μm) nuller and the cophasing system (visible) dedicated to the real-time control of the OPD/tip/tilt inside the payload. A laboratory breadboard of the payload is under definition and should be built in 2007.
The proposed way to tune the output beam is to use the diffraction effect with the so-called PMDG (Programmable Micro Diffraction Gratings ) diffractive MEMS. In that case, small moving structures can form programmable gratings, diffracting or not the incoming light.
In the proposed concept, the MOEMS is placed in the focal plane of a first diffracting stage (using a grating for instance). With such implementation, the MOEMS component can be used to select some wavelengths (for instance by reflecting them) and to switch-off the others (for instance by diffracting them). A second diffracting stage is used to recombine the beam composed by all the selected wavelengths. It becomes then possible to change and adjust the filter in λ and Δλ.
This type of implementation is very interesting for space applications (Astronomy, Earth observation, planetary observation). Firstly because it becomes possible to tune the filtering function quasi instantaneously. And secondly because the focal plane dimension can be reduced to a single detector (for application without field of view) or to a linear detector instead of a 2D matrix detector (for application with field of view) thanks to a sequential acquisition of the signal.
In that context, Alcatel Alenia Space has developed a nulling breadboard for ESA in order to demonstrate in laboratory conditions the rejection of an on-axis source. This device, the Multi Aperture Imaging Interferometer (MAII) demonstrated high rejection capability at a relevant level for exoplanets, in singlepolarized and mono-chromatic conditions.
In this paper we report on the new multi-axial configuration of MAII and we summarize our late nulling results.
View contact details
No SPIE Account? Create one
