Optical Path
The light from the primary hits the adaptive secondaries (AdSecs). From there the tertiaries send the f/15 beams towards the LBTI Bent Gregorian Focal Station. The visible light (λ < 1μm) is redirected by the dichroic entrance window toward the pyramid sensor wavefront sensor (WFS) units. The infrared light is allowed to pass to the LBTI Universal Beam Combiner (UBC). The UBC is cryogenically cooled to maintain good performance in the infrared. The UBC is designed to reimage the two f/15 focal planes to a common focal plane with an f/15 envelope with optimized the image overlap, phase difference and image quality over a large field-of-view. The light from the beam combiner comes to focus ~ 125mm inside the entrance window for the Nulling and Imaging Camera (NIC).
Fig.2 – Schematic of UBC light path. Some liberty has been taken with the fold angles for clarity. Figure courtesy of Spalding et al. 2018
Fig.3 – Schematic of light path in NIC cryostat as of spring 2018. Figure courtesy of Spalding et al. 2018
The NIC houses the L and M band Infrared Camera (LMIRcam), and the Nulling Optimized Mid Infrared Camera (NOMIC). Light is split after the focal plane by a trichoric that sends 3-5μm light to LMIRcam while reflecting 2-2.4μm light to the phase camera (PhaseCam) and 8-13μm to NOMIC. A window can be used in place of the trichoric in order to observe bluer wavelengths with LMIRcam to take advantage of the full sensitivity range of the detector.
