The fringe and flexure tracking detector of the LBT LINC-NIRVANA beam-combiner instrument

Abstract

LINC-NIRVANA is a near-­infrared (1-­2.4 micron) beam-­combiner instrument for the Large Binocular Telescope (LBT). LINC-NIRVANA is being built by a consortium of groups at the Max-­Planck-­Institut fur Astronomie in Heidelberg, the Osservatorio Astrofisico di Arcetri in Florence, the Universitat zu Koln, and the Max-­Planck-­Institut fur Radioastronomie in Bonn. The MPI fur Radioastronomie is responsible for the near­-infrared detector for the fringe and flexure tracking system (FFTS). We describe the design and construction of the detector control electronics as well as the first laboratory measurements of performance parameters of the NIR detector for the fringe and flexure tracking system of the LBT LINC-NIRVANA instrument. This detector has to record LBT interferograms of suitable reference stars in the FOV at a frame rate of the order of 200 frames per second using, for example, 32 x 32-­pixel subframes. Moreover, special noise reduction techniques have to be applied. The fringe-­tracker interferograms are required for monitoring and closed-­loop correction of the atmospheric optical path difference of the two LBT wavefronts (see C. Straubmeier et al., "A fringe and flexure tracking system for LINC-NIRVANA: basic design and principle of operation"). We will describe our laboratory measurements of maximum frame rate, readout noise, photometric stability, and other important parameters together with first measurements of laboratory simulations of LBT interferograms.