HARMONI is the first light, adaptive optics assisted, visible and near-infrared integral field spectrograph for the European Southern Observatory’s Extremely Large Telescope (ELT). As a ‘work-horse’ instrument, HARMONI will offer low, medium, and high spectral resolution volume phase diffraction gratings (VPH) across the I, z, J, H, and K-bands, operating at four spatial sampling scales including at the diffraction limit of the ELT. Consequently, understanding and controlling sources of wavefront error (WFE) is of critical importance to the instrument performance. We present a comprehensive overview of the WFE performance verification for the VPH element of the HARMONI infrared grating module. In collaboration with Wasatch Photonics, we compare the measured WFE at different test wavelengths to investigate the presence of any chromatic dependence or lack thereof. Finally, we discuss the origin of the observed wavefront error and the effectiveness of mitigation techniques such as magnetorheological finishing.
HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. It covers a large spectral range from 450 nm to 2450 nm with resolving powers from 3500 to 18000 and spatial sampling from 60 mas to 4 mas. It can operate in two Adaptive Optics modes - SCAO (including a High Contrast capability) and LTAO - or with NOAO. The project is preparing for Final Design Reviews. HARMONI is a work-horse instrument that provides efficient, spatially resolved spectroscopy of extended objects or crowded fields of view. The gigantic leap in sensitivity and spatial resolution that HARMONI at the ELT will enable promises to transform the landscape in observational astrophysics in the coming decade. The project has undergone some key changes to the leadership and management structure over the last two years. We present the salient elements of the project restructuring, and modifications to the technical specifications. The instrument design is very mature in the lead up to the final design review. In this paper, we provide an overview of the instrument's capabilities, details of recent technical changes during the red flag period, and an update of sensitivities.
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