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SPIRou / Infrared SpectroPolarimeter

2017 September: A second pupil slicer for SPIRou

SPIRou gets a new pupil slicer for its cryogenic spectrograph

A second pupil slicer

The second SPIRou pupil slicer during
tests at IRAP / OMP
(©S.Chastanet – CNRS/OMP)

The second pupil slicer of the SPIRou spectrograph was manufactured and delivered at IRAP / OMP by Winlight Optics, in South-Est France. This slicer duplicates the previous one in its functionalities ( with slight changes to improve its overall performances. The best of the two slicers will be used for observations while the second one will act as a spare if the main one gets damaged during operations.

This extremely compact opto-mechanical device is positioned at the entrance of the spectrograph to split the image coming out of the triple 90-µm fiber (at beam aperture f/4) into a series of 12 images (3 sets of 4 images, with one set per fiber) aligned in a 1.5-mm slit that feeds the spectrograph (at beam aperture f/8). In addition to feeding the spectrograph with maximum efficiency with no loss in spectral resolution, the slicer is equipped with octagonal fluoride fibers enhancing the scrambling of the incoming light and hence the stability of the image delivered to the spectrograph.

The various pictures illustrate the complexity of this miniature optical system consisting of a 8mm collimator, a pupil-slicing mirror (4 tilted flat mirror sections), a mirror stack (12 tilted 0.11-mm mirrors assembled by molecular adhesion) and a V-groove assembly hosting the three 90-µm octagonal fibers.

Comparison tests with the first slicer and final acceptance are ongoing, carried out by Yoan Micheau from IRAP / OMP.

Second slicer #2

Internal view of the slicer miniature optical system (©S.Chastanet – CNRS/OMP)

Second slicer #3

Light is injected through the 90-µm fibers positionned in v-grooves below the pupil slicing mirror, and comes out as a triple set of 4 slices formed on the mirror stack above the slicing mirror.
(© S. Chastanet – CNRS/OMP)

Second slicer #1

Testing the pupil slicer on the IRAP / OMP test bench (© S. Chastanet – CNRS/OMP)