Reference and sample spectra of N₂ ice, measured by the TPS (solid lines) and FTIR (dashed lines) spectrometers at specified deposition steps, t_dep, and normalized by the maximum of the corresponding reference spectrum (for convenience). The low-frequency gray-shaded area shows the spectral range where distortions are expected owing to the THz beam diffraction at the sample aperture (Giuliano et al. 2019). The orange-shaded area near ≃2.0 THz (enlarged in the inset for clarity) indicates where the TPS and FTIR data overlap. The sensitivity of the TPS and FTIR measurements is characterized by the standard deviation of the corresponding instrumental noise, σ_TPS and σ_FTIR, as described by Gavdush et al. (2022).