Context. Exoplanet science has made staggering progress in the last two decades, due to the relentless exploration of new detection methods and refinement of existing ones. Yet astrometry offers a unique and untapped potential of discovery of habitable-zone lowmass planets around all the solar-like stars of the solar neighborhood. To fulfill this goal, astrometry must be paired with high precision calibration of the detector. Aims. We present a way to calibrate a detector for high accuracy astrometry. An experimental testbed combining an astrometric simulator and an interferometric calibration system is used to validate both the hardware needed for the calibration and the signal processing methods. The objective is an accuracy of 5 × 10 −6 pixel on the location of a Nyquist sampled polychromatic point spread function. Methods. The interferometric calibration system produced modulated Young fringes on the detector. The Young fringes were parametrized as products of time and space dependent functions, based on various pixel parameters. The minimization of function parameters was done iteratively, until convergence was obtained, revealing the pixel information needed for the calibration of astrometric measurements. Results. The calibration system yielded the pixel positions to an accuracy estimated at 4×10 −4 pixel. After including the pixel position information, an astrometric accuracy of 6 × 10 −5 pixel was obtained, for a PSF motion over more than five pixels. In the static mode (small jitter motion of less than 1 × 10 −3 pixel), a photon noise limited precision of 3 × 10 −5 pixel was reached.
The reduction of systematic effects is necessary to improve the accuracy in imaging and astrometry. For example, in Euclid Mission which aims at carrying out accurate measurements of dark energy and quantifying precisely its role in the evolution of the Universe, systematic effects need at be controlled to a level better than 10 −7 (Euclid, Science Book). To achieve this goal, a high-level of knowledge of the system point spread function (PSF) is required. This paper follows the concept-paper presented at the last SPIE conference 1 and gives the recent developments achieved in the design of the test bench for the intrapixel sensitivity measurements. The measurement technique we use is based on the projection of a high spatial resolution periodic pattern on the detector using the self-imaging property of a new class of diffractive objects named continuously self-imaging gratings (CSIG) and developed at ONERA. The principle combines the potential of global techniques, which make measurements at once on the whole FPA, and the accuracy of spot-scan-based techniques, which provide high local precision.
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