The Theoretical and Applied Optics Department (DOTA) of ONERA proposes a full-time post-doctoral position in optical design / signal processing (18 months), to deal with the investigation of robust and efficient signal processing for innovative stationary Fourier transform infrared spectrometers.

Context

There is a need for compact, hand-held, inexpensive spectrometers for the measurement of spectral signatures of agents, high temperature gases or ambient temperature objects. For measurements of weak signals in the infrared spectral range, the most part of the existing spectrometers are based on the technique of Fourier transform (FT) spectroscopy and use a Michelson interferometer with a scanning mechanism. For radiance measurements of rather low-temperature objects like soils or foliage, the entire spectrometer should be cooled to minimize the instrument self-emission and to assure a good definition of the field of view. For this, we have developed stationary concepts of FT spectrometers based on the use of a two-wave interferometer and a 2D focal plane array. Such instruments are well-suited for measurements on large spectral range (typically from 2.5 µm to 10 µm), with a moderate spectral resolution (of typically 10 cm-1), at potentially high rates (up to 200 Hz) and with good signal-to-noise ratios. The first spectra obtained with these prototypes are very promising, but some improvements are now required in order to fully meet potential applications standards.

Objectives of the post-doctoral position

In order to optimize current interferograms processing, the applicant will have first to improve our current direct model, then to perform its robust inversion, and finally to evaluate the proposed methodology on a benchmark of spectra.

This includes:

-         the development of a model of the observation function describing interferogram fringes. Some parameters like the optical path difference of pixels can be quite challenging to estimate, and this step will involve processing of measurement database, along with specification of further experiments

-         a relevant analysis of existing regularized inversion methods, which enable to account for a priori information on spectra, and selection of the more suitable for obtaining robust spectra from experimental data

-         the valorisation of results by publications in international conferences and journals.

The applicant must hold a PhD in optics or signal processing or have a good experience in engineering applied to these fields.