A discussion on molecular absorption noise in the terahertz band

This paper focuses on molecular absorption noise caused by molecular absorption in the higher frequency bands, such as THz band (0.1–10 THz). This transmission induced noise has been predicted to exist in the THz band, since the conservation of energy requires the conservation of the absorbed energy in the medium. There exist multiple models for the molecular absorption noise. Most of them focus only on the transformation of the absorbed energy directly into antenna temperature. This paper aims at giving additional perspectives to the molecular absorption noise. It is shown that the molecular absorption noise can be investigated with multiple different approaches, strongly affecting on the predicted strength and behavior of the noise. The full molecular absorption noise model is not given in this paper. Instead, we study the molecular absorption noise from different perspectives and give their derivations and the general ideas behind the noise modeling.