IBIS 2.0: optical layout and polarimetric unit of the Interferometric BIdimensional Spectrometer 2.0

The IBIS 2.0 Interferometric BIdimensional Spectrometer 2.0 instrument combines two tunable Fabry-Ṕerot interferometers, narrowband interference filters, a polarimetric unit, fast cameras, and a proper Instrument Control System to perform high-resolution solar spectropolarimetric observations at high cadence with short exposures. A previous version of the instrument, named IBIS, operated at the Dunn Solar Telescope (DST) of the National Solar Observatory (NSO) from 2003 to 2019. IBIS 2.0 is planned to enter operations over the spectral range 580-860 nm at the Teide Observatory in 2023. In this paper we describe the final optical layout adopted for IBIS 2.0 along with its polarimetric unit, which is realized with two Liquid Crystals Variable Retarders and a Wollaston prism acting as a Polarizing Beam Splitter. We also present the final design of the Instrument Control System, the expected performances of the IBIS 2.0 instrument, and the planned sequence of operations.