Far-infrared Array Receiver (FAR) for SOFIA

In this paper, we present the design for a 16-channel heterodyne array receiver for use on SOFIA. The array will be capable of using either hot-electron bolometers or membrane mounted Schottky diodes in efficient, low-cost waveguide mounts. Focal plane arrays will be constructed to target astrophysically important lines between approximately 1.9 and 3 THz. Due to the prevailing physical conditions in the interstellar medium, this frequency range is one of the richest in the FIR portion of the spectrum. An array receiver designed for this wavelength range will make excellent use of the telescope and the available atmospheric transmission, and will provide a new perspective on stellar, chemical, and galaxy evolution in the present as well as past epochs. The proposed system uses the most sensitive detectors available in an efficient optical system. The local oscillator will be a compact CO₂ pumped far-infrared laser specifically developed for SOFIA. The backend spectrometer will be a 4×4 array of acousto-optic spectrometers (AOS). The spectrometer utilizes proven hardware and technologies to provide broadband performance (≥1 GHz per AOS channel) and high spectral resolution (1 MHz). The proposed instrument will be the fastest and most sensitive heterodyne receiver ever to operate in its wavelength regime.