Optical Performance and Results from the Alignment and Testing of the Cameras for the MOONS Spectrograph.

The MOONS (Multi-Object Optical and Near-infrared Spectrograph) is a twin, fibre-fed spectrograph for the VLT. Each spectrograph is fed with 512 fibres, the light from which is dispersed into three arms covering the RI, YJ and H bands. A separate camera is provided for each band, requiring six cameras to be produced and individually aligned. All six cameras have been assembled, aligned and cryogenically tested. The RI and YJ cameras, have been successfully integrated into the MOONS instrument cryostat and two more, including at least one of the H-band cameras are expected to be fitted for the next cool-down. Following an overview of the optical design of the camera, this paper presents the mechanical design together with stray light analysis and the inclusion of baffling. Six sets of optics have been provided by Bertin Winlight and an overview of their metrology data is presented. After assembly and pre-alignment of the first set of optics into the camera housing, a series of static and dynamic tests were carried out to ensure that the optics would remain in alignment following handling, transportation and ESO specified earthquake conditions. The pre-alignment stage and subsequent mechanical tests are described together with results from displacement and impulse testing. Because of the steep aspheric surfaces of the camera optics each set must be aligned in tilt and de-space at cryogenic temperatures. The facility specifically designed to accommodate the cryogenic alignment and stability testing of the MOONS cameras is presented and the fine alignment process under both warm and cryogenic conditions is described. Results from the final alignment stage and the stability of alignment under cryogenic cooling are presented and discussed.