English: Phase shift (advance) at "internal" reflection (dense-to-rare incidence), including total internal reflection, for refractive indices of 1.55, 1.5, and 1.45 ("internal" relative to "external"). On the angle-of-incidence scale (horizontal axis), Brewster's angle is where δ_p (red) falls from 180° to 0°, and the critical angle is where both δ_p and δ_s (red and blue) start to rise again. To the left of the critical angle is the region of partial reflection, where both reflection coefficients are real (phase 0° or 180°) with magnitudes less than 1. To the right of the critical angle is the region of total reflection, where both reflection coefficients are complex with magnitudes equal to 1. In that region, the black curves show the phase advance of the p component relative to the s component, as exploited in the Fresnel rhomb. It can be seen that a refractive index of 1.45 is not enough to give a 45° phase difference, whereas a refractive index of 1.5 is enough (by a slim margin) to give a 45° phase difference at two angles of incidence.