MOEMS-based instruments could be the next stepping stone for ground-based and space telescopes, allowing for multi-object spectroscopy in a 2D field of view. These programmable slit masks will optimize the SNR and generate compact and efficient spectro-imagers for Universe and Earth observation. BATMAN, a MOEMS-based spectro-imager for Universe observation to be installed at the TNG at the Canaria Islands, uses a Digital-Micromirror-Device to split the light between its imaging and spectrograph arms. ROBIN, the BATMAN demonstrator, confirmed its feasibility and image quality over the FOV.
A new design for a DMD-based high-resolution spectro-imager for Universe observation is presented: a solution using only one detector for all the wavelength range is obtained. We are dividing the 370 – 950 nm wavelength range into four channels and a spectral resolution of 15 000 is achieved for every one of them, all within an image quality below two detector pixels. Moreover, the 3-mirror design of the instrument implies a high throughput in comparison to catadioptric systems which are more commonly used for this science case.
A new MOEMS-based spectro-imager for Earth observation has been designed, with constraints of wide 2D field of view (3°×1°), image quality (< 2 pixels = 11 μm) and compacity. The instrument is panchromatic with a medium spectral resolution between 1000 and 2000, fitting in a 40 cm × 50 cm × 90 cm box. A 3-mirror solution for both imaging and spectrograph arms has been designed, using only aspheric surfaces thus allowing for easier alignment and tolerancing.
Next-generation infrared astronomical instrumentation for ground-based and space telescopes could be based on MOEMS programmable slit masks for multi-object spectroscopy (MOS). MOS is used extensively to investigate astronomical objects optimizing the Signal-to-Noise Ratio (SNR): high precision spectra are obtained and the problem of spectral confusion and background level occurring in slitless spectroscopy is cancelled. Fainter limiting fluxes are reached and the scientific return is maximized both in cosmology, in galaxies formation and evolution, in stellar physics and in solar system small bodies characterization. We are developing a 2048 x 1080 Digital-Micromirror-Device-based (DMD) MOS instrument to be mounted on the 3.6m Telescopio Nazionale Galileo (TNG) and called BATMAN. A two-arm instrument has been designed for providing in parallel imaging and spectroscopic capabilities. BATMAN will be mounted on the folded Nasmyth platform of TNG. Thanks to its compact design, high throughput is expected. The two arms with F/4 on the DMD are mounted on a common bench, and an upper bench supports the detectors thanks to two independent hexapods. The stiffness of the instrument is guaranteed thanks to a box architecture linking both benches. The volume of BATMAN is 1.4x1.2x0.75 m3, with a total mass of 400kg. Mounting of all sub-systems has been done and integration of the individual arms is under way. BATMAN on the sky is of prime importance for characterizing the actual performance of this new family of MOS instruments, as well as investigating the new operational procedures on astronomical objects (combining MOS and IFU modes, different spatial and spectral resolutions in the same FOV, absolute (spectro-) photometry by combining imaging and spectroscopy in the same instrument, automatic detection of transients …). This instrument will be placed at TNG by beginning-2019.
The space mission Arago is proposed as a candidate to ESA’s Cosmic Vision M5 call by the UVMag consortium. Arago is dedicated to the study of the dynamic 3D environment of stars and planets. Thanks to a high-resolution UV and visible spectropolarimeter, the instrument will detect and characterize the magnetic fields of the stars, their environment and its impact on exoplanets. Scientific requirements impose a wide spectral range from 119 to 888 nm with a single full-Stokes polarimeter followed by two high-resolution spectrographs. To achieve these stringent specifications, a polychromatic concept of polarimeter has been studied and tested thanks to a R and T study funded by CNES. Using an optimized combination of Magnesium Fluoride plates followed by a polarization analyzer, it measures all four Stokes parameters with a constant efficiency over the spectral range. This is performed with a sequence of 6 sub-exposures acquired with different plate angles. The two orthogonal polarized beams coming out of the polarimeter feed two spectrographs. The UV spectrograph has a spectral resolution of at least 25000 over its spectral range, while the visible spectrograph works at least at 35000. Finally, to image the high-resolution spectra, a CCD detector and a MCP were chosen for the visible and UV arms of the instrument respectively.
This paper describes the complete optical design of Arago’s instrument, as proposed to ESA as an answer to its M5 call, from the 1.3-m diameter telescope to the detectors. The design of the polarimeter is presented as well as the unusual way of demodulating the polarization information, in order to have a polychromatic polarimeter working with the same efficiency from FUV to NIR. The optical design of the UV and visible échelle spectrographs and their detection chains are also presented, as well as the achieved performances.