The Simons Observatory Large Aperture Telescope (LAT) is a crossed Dragone optical design with a 6 meter diameter aperture to explore CMB science at small angular scales. The incoming light reflects off a 6 meter wide primary mirror (M1) and a 6 meter wide secondary mirror (M2) before coming to a focus at the LAT receiver (LATR). The LAT has a usable 7.8° field-of-view at 90 GHz. The focal plane of the telescope is perpendicular to the incoming light allowing the LATR to operate in a horizontal configuration; a separate mechanism is used to rotate the receiver about its long axis as the telescope elevation structure moves M1 and M2 in rotation. M1 and M2 are formed from aluminum panels backed by a carbon fiber support structure with the surface controlled by a series of actuators. Vertex Antennentechnik GmbH is manufacturing the LAT for delivery and installation in Chile in 2021.

The LAT couples incoming light to the LATR’s 13 optics tubes, each with a 35 cm diameter window aperture. The initial SO deployment will populate seven optics tubes with three 6” detector wafers in each, for a total of over 30,000 detectors. Light from the telescope passes through a set of ambient temperature hexagonal windows and infrared blocking filters at 80 K and 40 K before reaching the 4 K optics tube. Each optics tube contains three silicon lenses to refocus the light on the detector arrays. The detectors are cooled by the LATR’s cryogenic systems to 100 mK.

The Large Aperture Telescope Receiver (LATR) is being integrated and tested at the University of Pennsylvania under the direction of Professor Mark Devlin.