The AIV concept of SHARK-NIR, a new coronagraph for the Large Binocular Telescope

Abstract

SHARK-NIR is one of the forthcoming instruments of the Large Binocular Telescope second generation instruments. Due to its coronagraphic nature, coupled with low resolution spectroscopy capabilities, it will be mainly devoted to exoplanetary science, but its FoV of 18 x 18 arcsec and very high contrast imaging capabilities will allow to exploit also other intriguing scientific cases. The instrument has been conceived and designed to fully exploit the exquisite adaptive optics correction delivered by the FLAO module, which will be improved with the SOUL upgrade, and will implement different coronagraphic techniques, with contrast as high as 10-6 up to 65 mas from the star. Despite the wavelength range of SHARK-NIR is 0.96-1.7 um, the instrument is designed to work in synergy with SHARK-VIS and with LMIRcam, on board of LBTI. The contemporary acquisition from these instruments will extend the wavelength coverage from M band down to the visible radiation. The physical location of the instrument, at the entrance of LBTI, imposes dimensional constraints to the instrument, which had been kept very compact. The folded optical design includes more than 50 optical elements, among which 4 Off-Axis Parabolas, 1 Deformable Mirror for the compensation of the Non Common Path Aberrations from the FLAO Wavefront Sensor, 2 detectors and 3 different kinds of coronagraph: Gaussian Lyot, Shaped Pupil and Four Quadrant Pupil Mask. Most of these optics are located onto an optical bench 500 x 400 mm, which makes SHARK-NIR an extremely dense instrument. This, together with the presence of 4 off-axis parabolas and of coronagraphs, such as the Four Quadrant, poorly tolerant to misalignments, requires a careful alignment and test phase, which needs the fine adjustement of many hundreds of degrees of freedom. We will give here an overview of the opto-mechanical layout of SHARK-NIR and of the identified alignment procedure, mostly optical, planned to take place in 2018.