Description
HARMONI (High-Angular Resolution Monolithic Optical and Near-infrared Integral field spectrograph) is a first-generation instrument for the Extremely Large Telescope (ELT). It is currently under the final design reviews, and is expected to cover a spectral range between 470 and 2450 nm (not simultaneously) with resolving powers from 3300 to 18000. The light from the entire field of view of the instrument will be reformatted into four linear slits by the Integral Field Unit (IFU) subsystem, each of which feeds an independent spectrograph. One of the key modules constituting each of the four Integral Field Spectrographs (IFS) is the Infrared Grating Module (IGM), which will contain 10 transmission volume-phase holographic (VPH) gratings offering low, medium and high resolutions and mounted on a continuous rotary drive mechanism. Together with the collimator module, the IGM ensures that the deviation angle through each grating is optimal, and that the output angle is constant for all gratings. During this work, different prototype testing was performed to confirm that the stepper drive mechanism complies with the required repeatability (~7.5 µrad) and provides a resolution of 150 µrad per step, during homing and normal movements for grating selection, following the defined motion profile. The realisation of these tests, support the manufacture, assembly, integration and performance verification of the module.
