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The DPS mechanism will be exclusively utilized during the alignment and test phase. Upon completing the test phase, it will be mechanically locked at the best pre-determined focus so that it cannot be moved during the observation period.
The DPS has been conceptualized as a fixed and reproducible interface to the Main Bench Structure in the MICADO cryostat and as an adjustable unit containing the Detector Array mounted on the DPS frame installed on a linear guide on the base plate. A cryogenic linear actuator further acts as the linear guide during the alignment phase to bring the focal plane array into focus.
SHARK-NIR is an instrument which provides direct imaging, coronagraphic imaging, dual band imaging and low resolution spectroscopy in Y, J and H bands, taking advantage of the outstanding performance of the Large Binocular Telescope AO systems. Binocular observations will be provided used in combination with SHARK-VIS (operating in V band) and LMIRCam of LBTI (operating from K to M bands), in a way to exploit coronagraphic simultaneous observations in three different wavelengths.
A wide variety of coronagraphic techniques have been implemented in SHARK-NIR, ranging from conventional ones such as the Gaussian Lyot, to others quite robust to misalignments such as the Shaped Pupil, to eventually techniques more demanding in term of stability during the observation, as the Four Quadrant; the latter is giving in theory and simulations outstanding contrast, and it is supported in term of stability by the SHARK-NIR internal fast tip-tilt loop and local NCPA correction, which should ensure the necessary stability allowing this technique to operate at its best.
The main science case is of course exoplanets search and characterization and young stellar systems, jets and disks characterization, although the LBT AO extreme performance, allowing to reach excellent correction even at very faint magnitudes, may open to science previously difficult to be achieved, as for example AGN and QSO morphological studies.
The institutes participating to the SHARK-NIR consortium which designed and built the instrument are Istituto Nazionale di Astro Fisica (INAF, Italy), the Max Planck Institute for Astronomy (MPIA, Heidelberg, Germany) and University of Arizona/Steward Observatory (UoA/SO, Tucson, Az, USA). We report here about the SHARK-NIR status, that should achieve first light at LBT before the end of 2022.
This concept was only merely described and functionally tested in the framework of MAD, and subsequently, with a holographic diffuser. The latter produce a sort of random distribution of the light coming out from the pupil plane, leading to sort of inefficient modulation, as most of the rays are focused in the central region of the light diffused by such device. The bi-dimensional original grating is, in contrast, producing a well defined deterministic distribution of the light onto a specifically shaped pattern. A crude option has been already discussed as a possibility, and it is here generalized to holographic plates leading to various distribution of lights, including a circle whose diameter would match the required modulation pattern, or more cost effective approaches like the one of a square pattern. These holographic diffusers would exhibit also zero-th and high order patterns and the actual size of the equivalent modulation would be linearly wavelength dependent, leading to colour effects that requires a careful handling in order to properly choose the right amount of equivalent modulation.
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