arXiv subjects

Julien Michelot

Publications and source records attributed to Julien Michelot.

4 recordsLinked to original sources

arXiv2026

Pixel-Level Calibration for Space-Based High Precision Astrometry Using Young's Fringes

The detection of Earth-like exoplanets via astrometry necessitates centroiding precision at the 0.3 microarcsec level, thereby imposing stringent constraints on the focal plane geometry of space telescopes. The AGATE focal plane instrument, a proposed component of the NASA Habitable Worlds Observatory (HWO), aims to achieve this objective through the calibration of the intra-pixel response function of CMOS detectors to an accuracy of 50 micropixel (220 nm The present paper proposes a Young's fringes-based calibration method, derived from those employed by JPL and IPAG, for the purpose of mapping the pixel response barycenter offsets across the detector. Using a Pyxalis GIGAPYX-4600 CMOS sensor, we demonstrate via simulations and laboratory measurements that (1) a precision of 500 micropixel is achievable with 10,000 frames (current setup); (2) inter-pixel capacitance crosstalk and fringe hyperbolicity are dominating the errors at small and large scales, respectively; and, (3) an iterative inverse problem approach with a hyperbolic fringe model is proposed to overcome paraxial approximation limits for 1 Gpix focal planes. These results pave the way for on-board calibration of HWO's astrometric instrument, ensuring the sub-microarcsec precision required for exo-Earth detection.

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arXiv2025

System Analysis for a high-precision high-accuracy Astrometric instrument for HWO

This study presents a comprehensive system analysis for an instrument onboard the Habitable Worlds Observatory (HWO), designed for high-precision, high-accuracy differential astrometry, with the primary scientific goal to determine the mass of Earth-like planets around the nearest Sun-like stars. The analysis integrates the definition of the mission profile, the instrumental concept architecture, and an error budget that breaks down the key contributors to the sub-micro arcses precision required for a single measurement. A portion of this budget addresses photo-center estimation for both the target and calibration stars used in differential astrometry. Other major contributors are related to instrumental control of systematics in the reconstruction of differential angle measurements from pixel data (focal plane calibration) to on sky line of sight (telescope distortion calibration). End-of-mission astrometry requires multiple observations (typically 100) of the same target distributed over the mission lifetime. We assess the mission profile to estimate the fraction of survey time required for astrometric survey to achieve the science objective. The proposed architecture of the instrument concept is derived from error budget and mission constraints based on a large visible detector array composed of an assembly of multiple CMOS sensor chips resulting in an overall gigapixel focal plane. We evaluate the Technology Readiness Level (TRL) and propose a way forward reaching TRL 5 level for key technologies by the Mission Consolidation Review in 2029.

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arXiv2025

Experimental tests of the calibration of high precision differential astrometry for HWO

Many different scientific applications require sub-micro arcsecond precision astrometry, including researching rocky exoplanets in the vicinity of the Sun and studying dark matter. The Habitable Worlds Observatory (HWO) is a promising candidate to carry an astrometric instrument because it provides a stable, space-based telescope with a large aperture, which allows faint sources and small displacements to be observed. This paper presents the characterization of an appropriate detector for an astrometric instrument: the 46Mpx Gigapyx from Pyxalis. Moreover it explains the implementation of a testbed enabling interferometric characterization of pixel positions. Finally, the paper introduces a method for calibrating the telescope's optical distortion. This method was implemented in simulation and tested thanks to an optical bench developed at IPAG in France.

astro-ph.IM↗

arXiv2025

GIGAPYX sensor performance in space environments

We present the results of the GIGAPYX-4600 image sensor in space environment, more specifically under different types of irradiations (protons and heavy ions). The GIGAPYX-4600 is a state-of-the-art 46M pixel multi-purpose, backside illuminated CMOS image sensor. The sensor features high-speed (200 fps), low-noise (< 2e-rms), rolling shutter readout. It has been fabricated using 65 nm node CMOS technology, making use of capacitive deep trench isolation, thus exhibiting good MTF as well as excellent dark current characteristics. The GIGAPYX image sensor family is meant to be easily scalable thanks to a novel use of stitching technology. The assessed sensor features an impressive 46 Mpixels, but the sensor family is meant to be scaled up to 220 M pixels. The idea of this study was to investigate the radiation hardness of a commercially available off-the-shelf (COTS) image sensor that could be suitable for space-borne applications, such as earth observation or satellite vicinity surveillance. In the near future a radiation hard readout electronic for this sensor family will be made available off-the-shelf by Pyxalis. This presentation will overview the different sensor key performances evolutions after proton irradiation up to a total fluence of 2.3e11 p+/cm${}^2$ (62 MeV): dark current, dark current non-uniformity (DCNU), noise, non-linearity, saturation charge and photo-response non-uniformity (PRNU). As expected, degradations mostly occur on the dark current, DCNU and temporal noise. The orders of magnitude of the degradation are in the range of the already published high performance CIS technologies. Results obtained from heavy ions irradiations will demonstrate that the GIGAPYX is not only latch-up free at least up to 57 Mev.cm2/mg, but resistant to the blooming effects induced by a SET at pixel level thanks to its capacitive deep trench isolations. Various SEE effects have been studied, demonstrating encouraging results for such COTS device in order to fly, in particular in GEO orbit. All these radiations results will be used as inputs in designing space camera based on the GIGAPYX sensors, compatible with multiple-mission types.

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