arXiv subjects

Adrien Girardot

Publications and source records attributed to Adrien Girardot.

5 recordsLinked to original sources

arXiv2026

Pollux UV & FUV polarimeters: first lab results

Pollux is a high-resolution spectropolarimeter proposed by a European consortium for the Habitable Worlds Observatory (HWO). Its design covers a broad spectral range from the far-ultraviolet (FUV) to the near-infrared (97-1\,750 nm), with polarimetric channels relying on \ch{MgF2} birefringent optics in the mid- and near-UV (MUV-NUV), and on an innovative all-reflective polarimeter in the FUV, where no birefringent material is available. To validate these polarimeters, whose required polarimetric precision is $10^{-3}$, a dedicated vacuum ultraviolet test bench has been developed, with two configurations: one for the MUV-NUV range (120-290 nm) and one for the FUV range (98-120 nm). We present the first laboratory results obtained with this bench. On the MUV-NUV configuration, the full optical chain has been integrated: a first polarised spectrum of the deuterium lamp was acquired, the polarisation generation subsystem was validated against Mueller matrix predictions, and a first end-to-end polarimetric measurement was performed. On the FUV configuration, the windowless deuterium plasma source has been characterised, the alignment strategy of the K-mirror modulator has been implemented, and the mirror-based analyser has been manufactured and tested, showing a polarisation extinction ratio of 10 at 120 nm. These results demonstrate the operation of the bench and pave the way for the characterisation of the polarimetric precision of the Pollux polarimeters, increasing the Technology Readiness Level of UV spectropolarimetry for HWO.

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arXiv2026

Pollux: high-resolution precision spectroscopy and polarimetry for the Habitable Worlds Observatory

Pollux is a high-resolution spectrograph and spectropolarimeter (R from 65000 to 100000) covering a spectral range from 100 nm to 1750 nm, proposed by a European consortium to equip NASA s Habitable Worlds Observatory (HWO). This instrument aims to revolutionize the study of stellar and (exo)planetary systems, as well as cosmic ecosystems, by combining high spectral resolution, broad and simultaneous spectral coverage, temporal stability, and unique UV spectropolarimetric capabilities, thus opening a new parameter space for astrophysics.

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arXiv2026

Pollux: decisions affecting the optical architecture of a high-resolution spectrograph and polarimeter for the Habitable Worlds Observatory

POLLUX is a candidate European instrumental contribution to the Habitable Worlds Observatory. It is a high-resolution spectrograph with polarimetric capabilities, covering from the far ultraviolet (FUV; 100nm) to the near infrared (NIR; 1.75mum). Such a broad spectral coverage is achieved by splitting the instrument into five channels, each comprising an echelle spectrograph: FUV, medium-UV (MUV), near-UV (NUV), optical (OPT), and NIR. A set of custom-made dichroics enables simultaneity across the MUV, NUV, OPT, and NIR channels.We present the latest developments in the optical design of the three UV channels. Specifically, we estimate the impact of telescope residual jitter on resolving power and sampling and discuss possible options to enable pure spectroscopy in the FUV channel without implementing a fully retractable polarimeter and to compensate the defocus when inserting MUV and NUV polarimeters. Finally, we estimate the impact of detector size limitation and potential advantages of shrinking or extending the wavelength coverage in the NUV channel.

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arXiv2026

Pollux test bench: from NUV to FUV polarimetric measurements

Pollux is a high-resolution spectropolarimeter proposed by an European consortium for HWO. The current design of Pollux features four spectropolarimetric channels, three of which are in the UV range. For the near-UV (NUV) [236-472 nm] and mid-UV (MUV) [118-236 nm] channels, the polarimeters consist of waveplates and prisms made of MgF2, a birefringent material. However, no such birefringent material can be used for the far-UV (FUV) channel [100-123 nm]. Therefore, the polarimeter for this FUV channel is composed solely of mirrors in an innovative assembly. In this talk, we aim to detail the architecture of the test bench that will allow us to validate the performance of these different polarimeters, as part of the HWO GOMaP. Given that we are working in the vacuum ultraviolet (VUV) range, the test bench operates in a vacuum chamber in a clean room. We will discuss the adaptable architecture of the bench based on wavelength and the measurement methodology that we will implement to test if the polarimeters achieve the precision of $10^{-3}$ required for the Pollux instrument. With this test bench, we will successfully increase the Technology Readiness Level (TRL) of UV spectropolarimeters and, for the first time, develop a means to test FUV spectropolarimetry.

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arXiv2025

Space UV polarimeters

Several space missions are proposed or planned for the coming two decades dedicated or including mid- to high-resolution spectropolarimetry on a wide UV band. This includes the European instrument Pollux for the NASA HWO flagship mission, the NASA SMEX candidate Polstar, and the French nanosatellite demonstrator CASSTOR. We are developing UV polarimeters for these missions thanks to a R&D program funded by CNES. For the mid- and near-UV, i.e. above 120 nm, birefringent material (MgF2) can be used to produce a polarimeter. This is the baseline for Polstar, CASSTOR, and the MUV and NUV channels of Pollux. Prototypes have been built and tested with excellent results, and further tests are ongoing to fully characterize them. For the FUV channel of Pollux however, it is not possible to use this technology and we have instead studied a design based on mirrors only. We will present the various missions and instruments, their technical challenges, as well as the R&D work performed on UV polarimeters and the proposed design solutions.

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