The Ultraviolet Imager (UVI) is a challenging instrument developed in the frame of the SMILE mission, a collaboration between ESA and CAS. The UVI instrument is a CMOS-based ultraviolet camera developed to image Earth's northern auroral regions. It is centered on the 160-180 nm UV waveband, with a 10° × 10° field of view. At the core of the instrument, four thin film-coated mirrors guide light into its detector and ensure most of the signal filtering, crucial to achieve an out-of-band rejection ratio as low as possible to reject light from solar diffusion, dayglow and unwanted atomic lines. We developed an interferometric coating based on an MgF2/LaF3 multilayer stack deposited by ion-assisted electron-beam deposition. We gradually improved our evaporation setup to reach a high degree of homogeneity, precision and repeatability on the material thicknesses, over the entire mirrors surface. The reflectivity maximum is above 85% and the wavelength at which it occurs is adjustable within 1 nm, while the out-of-band reflectivity between 120 and 155 nm and between 200 nm and 1100 nm is kept below 6% on average never exceeding 8 %. The coating has been space qualified and shows stable performances in conditions representative of the instrument operation environment (thermal cycling under vacuum, radiations, UV exposure…). @en

We describe the state of development of a white light interferometer to characterize the cryogenic mirrors for GW detector on operation. We include the first experimental results from the proof of concept of the metrology instrument. The instrument will characterize the topology as well as the vibration of the mirrors. This development takes place in the frame of the E-TEST project. E-TEST is one of the technology demonstrators for the future Einstein Telescope (ET). ET is dedicated to the measure and characterization of gravitational waves. The prototype built by E-TEST includes a large silicon mirror of 40 cm diameter suspended by innovative vibration isolation hanging modules. To reach the detection specification, the mirror is cooled down at cryogenic temperatures around 20 K. Nevertheless, even after the isolation, the mirror may not reach perfect stability once at cryogenic temperatures. Furthermore, the mirror may experience surface topology changes and wavefront deformation due to the extreme variations in temperature and gradient. With our metrology instrument, we can obtain on a single camera frame a set of interferogram maps of the area observed on the mirror at different optical path differences. To do this, we design an innovative phase mask for a white light low-coherence interferometer. In addition, we implement new algorithms for the white light interferogram analysis, avoiding the limitations of the conventional Phase Shifting Interferometry algorithms.

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