Symmetrical three-layer thin-film combinations are described which eliminate the difference in phase shift on reflection, of the S and P components of light incident beyond the critical angle. These three-layer combinations have low Herpin equivalent indices, but high enough material indices so that the critical angle is not exceeded until the final interface. Phase compensation is achieved at greater angles of incidence than those which can be compensated by single-layer films.
PAUL MAUER, "Phase Compensation of Total Internal Reflection," J. Opt. Soc. Am. 56, 1219-1221 (1966)