A series of detector systems for MUSE

The 24 IFU from MUSE are equipped with 4K x 4K CCD detectors which are operated at cryogenic temperature around 160 K. The large size of the chip combined with a rather fast camera (F/2) impose strong positioning constrains. The sensitive surface should remain in an angular envelope of less than 30 arc sec in both directions. The ambitious goal of having the same spectrum format on every detector imposes also a very accurate positioning in the image plane. The central pixel has to be located in a square smaller 50 microns relative to the external references. The first part of the paper describes the mechanical design of the detector head. We concentrate on the various aspects of the design with its very complex interfaces. The opto-mechanical concept is presented with an emphasis on the robustness and reliability. We present also the necessary steps for the extreme optimization of the cryogenic performance of this compact design driven with a permanent view of the production in series. The techniques and procedures developed in order to meet and verify the very tight positioning requirements are described in a second part. Then the 24 fully assembled systems undergo a system verification using one of the MUSE spectrographs. These tests include a focus series, the determination of the PSF across the chip and a subsequent calculation of the tip/tilt and shift rotation of the detector versus the optical axis.