FEA of the MUSE opto-mechanical model and comparison with on-site measurements

The Multi Unit Spectroscopic Explorer (MUSE) - the Very Large Telescope (VLT)'s mainstay instrument - has enabled significant astrophysical discoveries for nearly a decade. This study aims to use the insights gained from MUSE to refine and enhance the design of BlueMUSE, the blue-optimised panoramic integral field spectrograph which is the next ambitous development for the VLT. While acknowledging the existing MUSE design's effectiveness and scientific contributions, the objective of this paper is to understand and improve upon its thermal stability aspects. Thermal fluctuations cause flux variations in the spectrograph traces captured by the detector, which could compromise the quality of the scientific data between calibration sessions. A detailed Finite Element Analysis (FEA) of the MUSE system was conducted using ANSYS Workbench, Zemax OpticStudio and Math-Works MATLAB to simulate thermal, structural, and optical behaviors. This involved creating a comprehensive model, including the Instrument Field Unit (IFU), Field Splitter Unit (FSU), Fold Mirrors (FM1, FM2), and lenses, with a focus on their thermal responses. Mechanical shifts due to temperature variations were integrated into a Zemax optical model to assess their impact on system stability. By comparing these simulation results with empirical data, the model's accuracy was verified, and key areas for further thermal optimization were identified. The study also explores potential improvements for the anticipated BlueMUSE instrument, which could influence the design of future spectroscopic instruments.