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CAGIRE is the near infrared camera of the Colibrí robotic telescope, designed for the follow-up of SVOM alerts, mainly Gamma Ray Bursts (GRBs), and the quick imaging of sky regions where transient sources are detected by the SVOM satellite. CAGIRE is based on the Astronomical Large Format Array (ALFA) 2k x 2k SWIR sensor from the French consortium CEA-LYNRED. In the context of CAGIRE the sensor is operated in “Up the Ramp” mode to observe the sky in a square field of view of 21.7 arcmin on a side, in the range of wavelengths from 1.1 to 1.8 μm. An observation with CAGIRE consists of a series of short (1-2 minutes) exposures during which the pixels are read out every 1.3 second, continuously accumulating charges proportionally to the received flux, building a ramp.
The main challenge is to quickly process and analyse these ramps, in order to identify and study the near infrared counterparts of the bursts, within 5 minutes of the reception of an alert. Our preprocessing, which is under development, aims at providing reliable flux maps for the astronomy pipeline. It is based on a sequence of operations. First, calibration maps are used to identify saturated pixels, and for each pixel, the usable (non saturated) range of the ramp. Then, the ramps are corrected for the electronic common mode noise, and differential ramps are constructed. Finally, the flux is calculated from the differential ramps, using a previously calibrated map of pixel non-linearities. We present here the sequence of operations performed by the preprocessing, which are based on previous calibrations of the sensor response. These operations lead to the production of a flux map corrected from cosmic-rays hits, a map depicting the quality of the fit, a map of saturated pixels and a map of pixels hit by cosmic-rays, before the acquisition of the next ramp. These maps will be used by the astronomy pipeline to quickly extract the scientific results of the observations, like the identification of uncatalogued or quickly variable sources that could be GRB afterglows.
The direct imaging of exoplanets using coronagraphic instruments provides a good example of an astronomical application that can greatly benefit from such developments. Exoplanets imaging is very demanding in terms of optical surface quality, however, the majority of coronagraphic instruments use off axis optics, which manufacturing of such optics could present some drawbacks: either the optics are cut out of a parent large mirror, resulting in a material loss, or the surfaces are machined with sub-aperture tools, resulting in high spatial frequency ripples which must be avoided for this application.
Thanks to 3D printing and topology optimisation we created an innovative warping harness design which can generate any off axis parabola shapes with only one actuator. We optimised the harness thickness distribution in order to reach non symmetrical deformation composed of astigmatism and coma. The warping is applied by micrometric screws and the high transmission factor of the system allows to keep stable the final error budget despite the error introduced by the warping harness fabricated by 3D printing. Several warping harness designs and materials were explored for the prototyping phase. This study is part of WFIRST satellite which will be launch in 2024 by NASA to observe galaxies via a wide field instrument and also perform exoplanet direct imaging via coronagraph. In the case of the WFIRST coronagraphic instrument, eight off axis parabolas are used to relay the beam from one pupil to another. We present the first prototyping results dedicated to the WFIRST off axis parabolas. Deformation surface results are performed by interferometric measurements and compared to Finite Element Analysis predictions.
We describe here the first concave curved CMOS detector developed within a collaboration between CNRS-LAM and CEA-LETI. This fully-functional detector 20Mpix (CMOSIS CMV20000) has been curved down to a radius of Rc =150mm over a size of 24x32mm2. We present here the methodology adopted for its characterization and describe in detail all the results obtained. We also discuss the main components of noise, such as the readout noise, the fixed pattern noise and the dark current. Finally we provide a comparison with the at version of the same sensor in order to establish the impact of the curving process on the main characteristics of the sensor.
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