I want to mention that heterodyne detection is a process of mixing two signals. For astronomical detection, a stellar signal is combined, or mixed with a stable, fixed-frequency signal (the “local oscillator”) onto a nonlinear detector; the frequency of the local oscillator (LO) is chosen to lie at the center of the band to be detected in the source. The multiplication of these two signals produces a detector response which contains frequencies equal to the sum and difference of the two input frequencies, while preserving the amplitude and phase information contained in the original stellar signal. Typically the difference frequency between the stellar and local oscillator signal frequencies (termed the intermediate frequency) is that which is desired because of the often greater flexibility of handling a relatively lower frequency signal. The heterodyne frequency conversion technique is particularly well-suited for detection of thermal infrared radiation, i.e. frequencies on the order of tens of THz. A mid-infrared stellar signal collected by a telescope may then be spatially mixed with radiation from a laser (which serves as the local oscillator), onto a photodiode which serves as the nonlinear (square law) detector. Intermediate frequencies on the order of GHz are typically obtained, and standard radio techniques are utilized for amplification, transmission,
filtering, recording, etc.
I hope this will help. I will attach links of few papers here. You may refer to these