= Adiabatic optical following in a twisted nematic
{title2=$|\Delta k|\gg|\phi'|$}
When the <birefringence> separation of optical propagation constants $\Delta k=2\pi\Delta n/\lambda$ is large compared with the spatial rate of <rotation> of the <optic axes>, light with <linear polarization> in a local eigenpolarization follows the twisting <nematic director>. Thickness alone is insufficient if <birefringence> vanishes. Strong field alignment along the propagation direction suppresses the transverse optical anisotropy and hence the quarter-turn polarization <rotation>.
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