A holographic optical element to measure the transparency of the atmosphere at the Rubin-LSST observatory

• Marc Moniez (LAL (CNRS/IN2P3))

Room: 200/0-Auditorium - Auditorium P. Lehmann A 1.20 m diameter auxiliary telescope equipped with a slitless spectrograph has been installed near the main 8.40 m telescope of the Rubin-LSST project. This device is designed to monitor variations in the transparency of the atmosphere as a function of wavelength and time, in order to know in real time the effective shape of the passbands of the main telescope. The spectrograph initially designed on the basis of a periodic grating was unable to obtain a good quality spectrum over the entire wavelength range (400nm to 1050nm) for reasons that will be explained in the seminar. We have developed a thin dispersive holographic optical element, which has been operational since February 2021, which has not only enabled us to obtain spectra with the best possible resolution, but also with a diffraction efficiency that is almost double that of the initial device. I will describe the stages of this project, the objectives of which are to achieve photometric accuracy of the order of one per thousand with the Rubin-LSST main telescope, and to improve the performance of images taken under non-photometric conditions.