We present in this proceeding the results of the test phase of the GRAVITY+ adaptive optics. This extreme AO will enable both high-dynamic range observations of faint companions (including exoplanets) thanks to a 40×40 sub-apertures wavefront control, and sensitive observations (including AGNs) thanks to the addition of a laser guide star to each UT of the VLT. This leap forward is made thanks to a mostly automated setup of the AO, including calibration of the NCPAs, that we tested in Europe on the UT+atmosphere simulator we built in Nice. We managed to reproduce in laboratory the expected performances of all the modes of the AO, including under non-optimal atmospheric or telescope alignment conditions, giving us the green light to proceed with the Assembly, Integration and Verification phase in Paranal.
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. MgF2 being 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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