Figure 1.

Wavefront spacing in TIR. Left panel: subcritical θ < θ_c; middle panel: critical θ = θ_c; right panel: supercritical θ > θ_c. Wavefronts are shown as heavy solid lines. The plane of incidence is the x-z plane as shown. The right panel shows that the wavefront spacing for a supercritical θ > θ_c is squeezed by geometry in the x direction to be smaller than the spacing demanded by freely propagating light in medium 1 (shown as light vertical dashed lines). This squeezing forces the electric field in the z direction to decay exponentially. The heavy dashed arrows indicate propagation direction. A phase shift exists between wavefronts in medium 3 versus medium 1 for the supercritical case, but to clarify the depiction of wavefront spacing, it is not shown here.