The upGREAT Dual Frequency Heterodyne Arrays for SOFIA

We present the performance of the upGREAT heterodyne array receivers on the SOFIA telescope after several years of operations. This instrument is a multi-pixel high resolution ([Formula: see text]) spectrometer for the Stratospheric Observatory for Far-Infrared Astronomy (SOFIA). The receivers use 7-pixel subarrays configured in a hexagonal layout around a central pixel. The low frequency array receiver (LFA) has [Formula: see text] pixels (dual polarization), and presently covers the 1.83–2.07[Formula: see text]THz frequency range, which allows to observe the [CII] and [OI] lines at 158[Formula: see text][Formula: see text]m and 145[Formula: see text][Formula: see text]m wavelengths. The high frequency array (HFA) covers the [OI] line at 63[Formula: see text][Formula: see text]m and is equipped with one polarization at the moment (7 pixels, which can be upgraded in the near future with a second polarization array). The 4.7[Formula: see text]THz array has successfully flown using two separate quantum-cascade laser local oscillators from two different groups. NASA completed the development, integration and testing of a dual-channel closed-cycle cryocooler system, with two independently operable He compressors, aboard SOFIA in early 2017 and since then, both arrays can be operated in parallel using a frequency separating dichroic mirror. This configuration is now the prime GREAT configuration and has been added to SOFIA’s instrument suite since observing cycle 6.