The dependence of the critical angle (ϕ_c in the figure) on the value of ε_3f < 0, above which the wave number κ_z is no longer limited by the value of ε_3f when this is negative. When ε_3f > 0 the value of must be less than ε_3f for propagation of hybrid homogeneous modes. If ε_3f < 0, there will be an angle ϕ_crit above which there will be propagation of inhomogeneous modes. The arrow in the diagram shows the critical angle when ε_3f = −2.7889.