Calculation of the thicknesses l_CO, I, l_CO, II and the complex refractive index n of the CO ice films (see Fig. 3). Panel a: time delays between the ballistic THz pulses of the reference (0) and sample (1) waveforms, δt₀₁; the first satellite pulse (2) and the ballistic pulse (1) of the sample waveform, δt₁₂; and the second satellite pulse (3) and the ballistic pulse (1) of the sample waveform, δt₁₃ (the pulses are delineated as in Fig. 3). Panels b and c: estimates for the thicknesses of the two ice films as a function of the total deposition time t_dep for the different deposition intervals of Δt_dep = 4, 5, and 6 min; the first assumption for the real part of the refractive index of ice is between and 1.255 ± 0.035; for the imaginary part we first set .