Upper row: neutral free-free (H⁻) and ion free-free emissivities for the model with E_c = 20 keV and δ = 5, observed at t = 2.0 s, at each of four wavelengths. Red shading indicates neutral free-free dominance, and blue shading ion free-free dominance. The lower row shows the corresponding contribution functions, showing the enhancement of the optical depth at longer wavelengths as the ion free-free opacity increases. For these parameters, panel f) shows the chromosphere to become completely opaque by 200 μm. The dashed lines show the pre-flare emissivities.