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MIRI Spectrometer Pre-Optics

Spectrometer Pre - Optics

The Spectrometer pre-optics houses the the Image Slicers and the Dichroic/Grating wheels. Light enters the SPO from directly from the IOC. Light passes from the Image slicer, through a series of mirrors, to the FPM. The FPM is in the main optics (SMO). The SMO is being built by Astron.


Dichroic Wheels

The Dichroic Wheels are fixed to the filter wheel, alongside the Grating Wheels. All of which sits inside the SPO housing. However, the Filter Wheel and the Grating Wheels are produced by Max-Planck-Institut fur Astronomie (MPIA) and Astron (respectively). The wheel comprises three working positions to move gratings and dichroics simultaneously. Each is located on separate wheel discs. The two wheels feed light in to the four spectrometer channels inside MIRI. The system has to operate in the cryovacuum of 7k (as well as ambient conditions) during a ground-test of 3 years on Earth and a mission period of up to 10 years in space.

Dichroic Wheel

Integral Field Unit

The integral field is located in the SPO between the APO and the spectrometer. The system contains an entrance pupil, an input fold mirror, an image slicer mirror and exit pupil, two re-imaging mirror arrays, an output fold mirror and the exit slit. Light enters the IFU through the entrance pupil as provided by the APO. The beam is then directed towards the image slicer mirror by a 45 degree fold mirror. The image slicer is located at a magnified imager of the telescope focal plane provided by the APO.

Image Slicer

The purpose of the image slicer is to split the image into a number of slices, N, and direct the N output beams towards a series of N slits. These slits form the entrance to the MIRI spectrometer. The image slicer mirror re-images the entrance pupil onto a line of exit pupils. Following the exit pupil an array of N re-imaging mirrors is used to transfer the image from the slicer mirror to the line of output slits. Each output slit is therefore an image of the corresponding slice of the slicer mirror.

Image Slicer

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