Thermal tests of birefringent plates in molecular adhesion for spatial ultra-violet polarimetry

Maëlle Le Gal; Coralie Neiner; Matthieu Louvel de Monceaux; Napoléon Nguyen-Tuong; Jérôme Parisot; Claude Collin; Jean-Michel Reess; Marion Bonafous; Cyrille Blanchard; Aurélien Pelleau; Pierre Baudoz; Martin Pertenais; Vincent Costes; Frank Brachet; Elsa Locatelli; Jean-Michel Desmarres

doi:10.1117/12.2561439

13 December 2020 Thermal tests of birefringent plates in molecular adhesion for spatial ultra-violet polarimetry

Maëlle Le Gal, Coralie Neiner, Matthieu Louvel de Monceaux, Napoléon Nguyen-Tuong, Jérôme Parisot, Claude Collin, Jean-Michel Reess, Marion Bonafous, Cyrille Blanchard, Aurélien Pelleau, Pierre Baudoz, Martin Pertenais, Vincent Costes, Frank Brachet, Elsa Locatelli, Jean-Michel Desmarres

Author Affiliations +

Proceedings Volume 11451, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV; 1145132 (2020) https://doi.org/10.1117/12.2561439
Event: SPIE Astronomical Telescopes + Instrumentation, 2020, Online Only

Conference Poster

Abstract

High-resolution spectropolarimetry is a technique used to study many astronomical objects including stellar magnetic fields. It has mainly been used on ground for optical and, more recently, infrared (IR) observations. Space mission projects including ultra-violet (UV) high-resolution spectropolarimetry, such as Pollux onboard LUVOIR proposed to NASA, are being studied in Europe under CNES leadership. Bringing a spectropolarimeter into space means that the instrument should be prepared for space environment including temperatures. The UV polarimeter we are considering is composed by a rotating modulator and an analyzer. Both components are made of magnesium fluoride (MgF₂). The modulator is a rotating block of waveplates in molecular adhesion, each plate having its own fast axis. The analyzer is a Wollaston prism, also made with molecular adhesion. MgF₂being birefringent, the plates and prism are anisotropic and will dilate and retract due to thermal changes differently along their fast and slow axes. Each plate having its own fast axis, the thermal changes will create stress at the interfaces, i.e. at the molecular adhesion between the plates. This study focuses on the most critical part: the plates of the modulator. To demonstrate the resistance of the modulator and increase its technological readiness level (TRL), an optical bench including interferometry has been set at the Paris Observatory. It allows us to observe in real time the state of the molecular adhesion between plates as they are submitted to thermal changes in a vacuum chamber. Additional samples have been tested in a thermal vacuum chamber at CNES. This article describes the modulator using molecular adhesion, the test experiments, and the conclusion of this thermal study. Although molecular adhesion broke in 2 samples during thermal cycling, most samples survived which provides encouraging results for this technique.

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Maëlle Le Gal, Coralie Neiner, Matthieu Louvel de Monceaux, Napoléon Nguyen-Tuong, Jérôme Parisot, Claude Collin, Jean-Michel Reess, Marion Bonafous, Cyrille Blanchard, Aurélien Pelleau, Pierre Baudoz, Martin Pertenais, Vincent Costes, Frank Brachet, Elsa Locatelli, and Jean-Michel Desmarres "Thermal tests of birefringent plates in molecular adhesion for spatial ultra-violet polarimetry", Proc. SPIE 11451, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation IV, 1145132 (13 December 2020); https://doi.org/10.1117/12.2561439

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