Optical, mechanical and electronic design and integration of POMM, a polarimeter for the Observatoire du mont Mégantic

Leclerc, Mélanie; Côté, Pascal; Duchesne, François; Bastien, Pierre; Hernandez, O.; d'Istria, Pierre Colonna; Demers, Mathieu; Girard, Martine; Savard, Maxime; Lemieux, Dany; Thibault, Simon; Brousseau, Denis

doi:10.1117/12.2054773

Cited by 2 publications

(2 citation statements)

References 6 publications

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“…The polarization measurement method requires sampling the signal at many discrete angular orientations [2]. The channel for sky background noise compensation adds a second rotation system placed 93.7 mm off-axis from the main star channel.…”

Section: Backlash-less Cascaded Rotating Stagesmentioning

confidence: 99%

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POMM: design of rotating mechanism and hexapod structure

et al. 2014

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The new high precision polarimeter for the "Observatoire du Mont Mégantic" (POMM) is an instrument designed to observe exoplanets and other targets in the visible and near infrared wavebands. The requirements to achieve these observation goals are posing unusual challenges to structural and mechanical designers.In this paper, the detailed design, analysis and laboratory results of the key mechanical structure and sub-systems are presented.First, to study extremely low polarization, the birefringence effect due to stresses in the optical elements must be kept to the lowest possible values. The double-wedge Wollaston custom prism assembly that splits the incoming optical beam is made of bonded α-BBO to N-BK-7 glass lenses. Because of the large mismatch of coefficients of thermal expansion and temperatures as low as -40°C that can be encountered at Mont-Mégantic observatory, a finite element analysis (FEA) model is developed to find the best adhesive system to minimize stresses.Another critical aspect discussed in details is the implementation of the cascaded rotating elements and the twin rotating stages. Special attention is given to the drive mechanism and encoding technology. The objective was to reach high absolute positional accuracy in rotation without any mechanical backlash.As for many other instruments, mass, size and dimensional stability are important critera for the supporting structure. For a cantilevered device, such as POMM, a static hexapod is an attractive solution because of the high stiffness to weight ratio. However, the mechanical analysis revealed that the specific geometry of the dual channel optical layout also added an off-axis counterbalancing problem. To reach an X-Y displacement error on the detector smaller than 35µm for 0-45° zenith angle, further structural optimization was done using FEA. An imaging camera was placed at the detector plane during assembly to measure the actual optical beam shift under varying gravitational loading.

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Section: Backlash-less Cascaded Rotating Stagesmentioning

confidence: 99%

“…The overall design of the supporting structure was also studied carefully because of the mass limit that can be counter balanced on the Mont-Mégantic telescope while preserving the overall stiffness for pointing accuracy. Note that the optical and electronics design of POMM is discussed in details in a separate paper by Leclerc [2].…”

Section: Introductionmentioning

confidence: 99%