arXiv subjects

Arnaud Striffling

Publications and source records attributed to Arnaud Striffling.

4 recordsLinked to original sources

arXiv2026

Modelling Fourier filtering wavefront sensors for PSD-based methods: the AOPERA tool

Compensation of the atmospheric turbulence thanks to adaptive optics (AO) has now become commonly used for VLT or ELT class telescopes in order to retrieve a resolution close to their diffraction limit. Following the increasing trend of AO system, there is also a stronger necessity for simulations in order to understand and predict their performance facing different observing conditions, that are the evolution of the atmospheric turbulence or the diversity of AO guide source. The so-called PSD based methods are well adapted to the demand thanks to their simplicity and speed. Moreover, they provide a comprehensive breakdown error budget and impact on focal plane, that is of high interest especially in the case of extreme adaptive optics. Their drawback is the challenge to describe non-linear wavefront sensors (WFS) such as the pyramid WFS or the Zernike WFS. There is a necessity to develop fast yet accurate methods to describe the behaviour of AO systems including sensitive WFS. We thus develop a method to compute the AO system response (electromagnetic phase power spectral density, and point spread function) including the non-linear behaviour of the wavefront sensor within PSD-based numerical tools. Mathematical formalism to describe the FF-WFS sensitivity combined to non-linearity management greatly improve the accuracy of description of AO systems through numerical simulations. After a mathematical description of the method, its numerical implementation is compared with end-to-end simulations using the OOPAO tool. Indeed end-to-end simulations are reproducing the response of AO systems with high fidelity, especially regarding WFS sensitivity and non-linearity. Similarity of results for the fitting error, temporal error and noise error proves the validity of our method in managing Fourier filtering WFS sensitivity and non-linearity.

astro-ph.IM↗

arXiv2026

RISTRETTO: Assembly and Testing of the Seven-spaxel, High-resolution, Diffraction-limited Spectrograph

The RISTRETTO project aims at the direct detection of the reflected light of extra-solar planets to measure albedos and detect possible biosignatures, using the high-contrast / high-resolution method. We report on the assembly, lab-testing and on-sky testing of the seven-spaxel high-resolution single-mode spectrograph which was built ahead of the rest of the instrument. The spectrograph is a high resolution echelle spectrograph build for high spectral fidelity being uder vacuum and thermally controlled. Once the assembly has been completed we had the chance to test it on sky using OHP 1.52 m telescope using the PAPYRUS AO system for injection in our spectrograph.

astro-ph.IM↗

arXiv2026

Closing the loop on-sky with a vector-Zernike wavefront sensor using a convolutional neural network as phase reconstructor

Context: The new giant segmented mirror telescopes will use adaptive optics to reach the fundamental limits in resolving power. To accomplish this, new wavefront sensors (WFS) have been designed to fulfill the requirements, but they may require non-linear reconstruction techniques to operate given the nature of the signal of the WFSs Aims: In this article we show that it is possible to use non-linear reconstructors to extend the dynamic range of one of the most sensitive wavefront sensors far beyond the designed limits: the Zernike wavefront sensor (ZWFS). Methods: We trained a convolutional neural network (CNN) completely in simulation to perform the phase reconstruction of a vector-ZWFS (v-ZWFS), a higher dynamic-range variant of the ZWFS. Contrary to the linear method, the CNN uses the information across the full frame to reconstruct the phase at each point, enabling it to resolve the ambiguities introduced by the periodic response of the ZWFS and thereby extend its effective capture range. We developed a two-step training strategy that ensured closed-loop stability and used a physically informed loss function to maximize the performance of the CNN. Results: We successfully closed the loop on-sky with the v-ZWFS using the CNN in observing conditions that the linear reconstructor could not converge to a stable flat wavefront. In cases where both reconstruction methods were working, the CNN outperformed the linear method in almost all cases, and in favorable seeing conditions we were even able to close the loop with the ZWFS acting as a first stage WFS, highlighting the extended dynamic range brought by the use of a non-linear wavefront reconstructor. Conclusions: We conclude that the use of non-linear wavefront reconstructor can extend the use cases of adaptive optics systems, especially when the WFS used shows highly non-linear behaviors.

astro-ph.IM↗

arXiv2026

Characterization and on-sky testing of photonic, AWG-based astronomical spectrographs

Astrophotonics is a field that intends to meet the needs of next-generation instruments at a small footprint, low cost, and high stability, compared to bulk-optics-based alternatives. Much development effort is driven by the stringent requirements of direct detection and characterization of exoplanets. Our team works in characterizing Arrayed-Waveguide Grating (AWG) chips for photonics-based, high-resolution, near infrared spectro-interferometry. AWG spectrographs allow to test the feasibility of photonic spectro-interferometers for exoplanet characterization, another step towards fully photonic instruments for astronomy. We present the current status of our AWG characterization and a preliminary on-sky qualification campaign at the PAPYRUS AO system. We present the CoLiBRIS-AWG spectrograph prototype built for on-sky testing, and preliminary results using our high-resolution (H band, R~18000) AWG for observations of Arcturus (alpha Bo\"otes) and Betelgeuse (alpha Orionis). This work contributes to assessing the capabilities of photonic spectroscopy for the development of future compact instruments.

astro-ph.IM↗