Vibration measurements at the Large Binocular Telescope (LBT)

Abstract

The Large Binocular Telescope (LBT) is an international collaboration, with partners from the United States, Italy, and Germany. The telescope uses two 8.4-meter diameter primary mirrors to produce coherent images with the combined light along with adaptive optics. The correct functioning and optimum performance of the LBT is only achieved through a complex interplay of various optical elements. Each of these elements has its individual vibration behaviour, and therefore it is necessary to characterize the LBT as a distributed vibration system. LINC-NIRVANA is a near-infrared image-plane beam combiner with advanced, multi-conjugated adaptive optics, and one of the interferometric instruments for the Large Binocular Telescope (LBT). Its spectral range goes from 1.0 μm to 2.45 μm, therefore the requirements for the maximum optical path difference (OPD) are very tight (λ/10 ~ 100 nm). 1 During two dedicated campaigns, the vibrations introduced by various actuators were measured using different kinds of sensors. The evaluation of the obtained data allows an estimation of the frequency and amplitude contributions of the individual vibration sources. Until the final state of the LBT is reached, further measurements are necessary to optimize and adapt the equipment and also the investigated elements and configurations (measurement points and directions, number of sensors, etc.).