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Image slicers (SLI) are now standard equipment in astronomical instrumentation, particularly for Integral Field Spectroscopy (IFS). Our team at the Advanced Optical Fabrication Infrastructure (AOFI) has been tasked with the fabrication of the slicer-based IFU for GIRMOS (Gemini InfraRed Multi-Object Spectrograph), which contains 42 250-μm wide slices along with the corresponding pupil and field mirrors. Diamond turning image slicers is complicated as they often include tilted slices smaller than 500-μm wide. The surface finish of diamond-turned optics must be optimal in astronomical applications such as integral field spectroscopy. Here we present a test plan and characterization of the GIRMOS SLI system. One notable challenge is the disparity between room temperature testing and the cryogenic environment of the actual system. This requires the design of a warm model, which has been numerically validated. A comprehensive metrology process is implemented, utilizing equipment such as a Talysurf PGI Freeform profilometer, a ZYGO Verifire HD Fizeau interferometer, a coordinate measuring machine (CMM), a point source microscope (PSM) equipped with a motorized gimbal mount, a scanning electron microscope (SEM), and a custom SLI-M1 test bench. The test bench facilitates verification of intermediate pupil positions, calculation of the slices' tilts and curvatures, measurement of diffraction efficiency, and estimation of surface roughness through total integrated scatter (TIS) analysis. Additionally, the bench is used to characterize the pseudo-slit output by replacing front-end optics and enables the measurement of tilts on all surfaces using a precision motorized gimbal stage. The test plan presented establishes a robust methodology for comprehensive characterization, essential for high precision integral field spectroscopy in astronomical observations.
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