In the fields of space, astronomy, and defense, the emergence of cooled infrared (IR) imaging systems with large focal plane array (FPA) formats and increasingly smaller pixels makes measuring the spatial response of pixels essential. This quantity reflects, on the one hand, the spatial distribution of the signal collected by the pixels and, on the other hand, through its modulation transfer function (MTF), the detector's ability to accurately reproduce the spatial details of the observed scene. It is a key tool:

•    for technologists seeking to optimize infrared detection structures.

•    for systems engineers working on high-performance optronic spatial instruments.

However, several constraints complicate these measurements: on the one hand, the cryogenic cooling required for these high-performance IR detectors, whose intrinsic and ambient background infrared fluxes are often a significant limitation, and on the other hand, the miniaturization of pixels, whose size tends to approach the wavelength. Additionally, there is a growing need for spectral measurements (at different light wavelengths) of this spatial response of infrared FPAs, in connection with the development of multispectral and hyperspectral systems. This raises questions about the influence of the infrared spectrum on the spatial response of such detectors, hence the need for "spectro-spatial” measurement and the importance of monochromatic MTF measurements.

To address these challenges, the ONERA laboratory has designed the MIRCOS cryogenic bench, a unique and versatile platform. This bench incorporates various pattern projection approaches (cryogenic optics, interferometric techniques, etc.), which are being continuously improved through ongoing research in order to achieve a metrological level of measurement of the spatial response of infrared detectors. Among the most promising methods (for addressing the challenge of small pixels and spectral requirements), interferometric techniques are based on comparing an interferogram imaged by the detector array with a simulated interferogram prior to detection. Through Fourier space processing, the 2D transfer function can be deduced from the loss of spatial information between these two quantities. However, the projected interferogram must both contain spatial frequencies of interest for small pixels and be perfectly simulated so as not to introduce significant bias into the restored transfer function. The proposed thesis thus aims to improve measurement performance by using a new innovative optical grating concept that allows 2D spatial frequencies to be projected onto a detector array, the amplitude of which is detected heterodynously along the optical axis. The  concept of this grating was initiated during the thesis of Pierre Arrondeau (thesis co-funded CNES-ONERA), opening up numerous scientific perspectives for addressing the issue of spatial response measurement.

Thanks to its specific signature along the optical axis, it enables precise deconvolution of MTF measurements using monochromatic illumination. A prototype in the infrared band [1-2] µm has already demonstrated the value of such a signature for metrological applications. The idea is therefore to continue along this path, with several scientific aspects to be addressed: optimization of patterns projected in the thermal infrared ([3-5] then [8-12] µm) by propagation simulation, possibility of hyperspectral measurement of the MTF, discretized data with a high signal-to-noise ratio covering both low spatial frequencies (for precise MTF normalization) and high spatial frequencies (required by small pixels). The project will be divided into two parts, theoretical and experimental: the doctoral student will be required to model the physical phenomena involved in the measurement, but also to design and develop new components and experimental benches. The student will benefit from the experience acquired by the team over several years working with the MIRCOS test bench and will be able to develop advanced skills in optics, interferometry, cryogenics, and infrared detection.

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For more Information about the topics and the co-financial partner (found by the lab!); contact Directeur de thèse - jerome.primot@onera.fr

Then, prepare a resume, a recent transcript and a reference letter from your M2 supervisor/ engineering school director and you will be ready to apply online before March 13th, 2026 Midnight Paris time!