LINC-NIRVANA Adaptive Optics Control Application

Abstract. LINC-NIRVANA[1] is an imaging Fizeau interferometer, for use in near infrared wavelengths, being built for the Large Binocular Telescope[2]. Multi-conjugate adaptive optics (MCAO) increases the sky coverage and the field of view over which diffraction limited images can be obtained[3]. For its MCAO implementation, Linc-Nirvana utilizes four total wavefront sensors; each of the two beams is corrected by both a ground-layer wavefront sensor (GWS) and a high-layer wavefront sensor (HWS). The GWS controls the adaptive secondary deformable mirror (DM)[4], which is based on an DSP slope computing unit[5]. Whereas the HWS controls an internal DM via computations provided by an off-the-shelf multi-core Linux system. Using wavefront sensor data collected from a prior lab experiment, we have shown via simulation that the Linux based system is sufficient to operate at 1 kHz, with jitter well below the needs of the final system. Based on that setup we implemented an adaptive optics loop control application which includes the back-end number crunching loop pipeline from camera readout to the DM. All intermediate steps of the loop are controlled by modular engineering GUI front-ends for diagnostic and configuration. Those engineering front-ends can either be used together with the slope computing unit (Basic Computation Unit BCU) which is used by the GWS and the initial Pathfinder[6] setup or with the Linux based system (for MCAO operation of the HWS). The implementation of the Linux based system is done similar to the internal process of the BCU. In this way both systems provide the same functionalities an