Fabrication and characterization of aluminum image slicers

In order to study distant galaxies and extra-solar planets, image slicers are now widely used in most integral field spectrographs (IFSes). Nonetheless, their multiple small tilted surfaces make them particularly difficult to manufacture, but equipment such as that of AOFI (Advanced Optical Fabrication Infrastructure) of University Laval eases this process. In this regard, the AOFI team has been tasked with the fabrication and characterization of the image slicer of the GIRMOS (Gemini Infra-Red Multi-Object Spectrograph) instrument. However, first attempts to produce small slicer prototypes have shown an issue with a monolithic diamond turning approach: manufacturing time. To address this matter and minimize tool wear while achieving good surface quality and optical performance, we have developed a unique manufacturing procedure, based on aluminum mechanical sub assemblies. This paper discusses this strategy and the metrology tests that were then applied to the image slicer of GIRMOS, including the analyses of surface roughness and other parameters such as tilts, curvature and active area.