Reference : UMR7326-ANAMEK-046
Workplace : MARSEILLE 13
Date of publication : Wednesday, September 14, 2022
Scientific Responsible name : Benoit Neichel
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 December 2022
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly
Description of the thesis topic
For direct imaging of exoplanets from the ground, the performance requirements of Adaptive Optics are extreme because any residual phase results in residual starlight that reduces the potential detectability of planets. The fundamental limits of such instruments lie in the quality of the wavefront measurement, with photon noise as a fundamental limit. Wavefront Sensing (WFS) is strongly linked to technological constraints on detectors, and pushes them towards ever faster detectors, without readout noise, and at ever larger sizes.
In this context, Fourier filtering WFSs are among the most sensitive available and are therefore excellent candidates for XAO instruments. For more than 5 years, our group (LAM/ONERA) has strongly pushed the development and concept validation of new Fourier filtering WFSs, in order to gain in maturity on their use, but also to propose innovative solutions (of filtering concept or exploitation of raw data coming from the ASO) to improve the sensitivity.
But sensitivity is only one side of WFS optimization, and often optimizing sensitivity comes at the cost of linearity. For example, if the performance of the non-modulated pyramid seems excellent, in practice it is very difficult, if not impossible, to make this device work, because of the non-linearity and saturation of this sensor.
We have recently shown that it would be possible to use several wavelengths in parallel, and use the chromatic scaling of the turbulence (known theoretically) to calibrate the signal actually measured. In other words, we compare the reconstructed phase at different wavelengths with the one expected theoretically, and this allows us to estimate and compensate for linearity errors. We could benefit from the extreme sensitivity of WFSs such as the unmodulated pyramid, but for 1st stage WFSs, which would see the full turbulence. This would simplify future XAO systems while approaching the ultimate performance of this type of analyzer.
The objectives of the thesis are:
1. Develop end-to-end simulations to model the exact behavior of a Fourier Filtering WFSs.
2. Demonstrate in simulation the concept of the "rainbow pyramid", and the robustness of this new sensor to large phase variations
3. Extrapolate the results to non-atmospheric phases, such as the famous "petalling" or "Low Wind Effect". Here the wavelength leverage should allow to resolve the 2pi indeterminations.
4. Set up a bench to experimentally validate the new concepts of linearization / non-atmospheric aberration measurements.
For the experimental aspects, we propose to use the PAPYRUS bench, available at LAM and OHP, on which a "classical" pyramid analyzer channel is available.
The Laboratory (LAM) will first provide access to the E2E simulation tools, and to the computing clusters. The LAM will then provide access to the experimental benches, with LOOPS and PAPYRUS.
The student will be integrated in the R&D Group, under the direction of Benoit Neichel.
Master in instrumentation, optics, physics or astronomy.
We talk about it on Twitter!