Electric Fields Parallel to the Helix Axis

Many of the magneto-optic effects described earlier are readily observed in electric fields when the magnetic free energy term magnetic [= ( is replaced by the 

For the distorted structure E the helix axis will have small components in the x direction as before, and therefore in the small deformation approximation we have 

There is a further force/j, due to changes in the dielectric tensor as the chiral nematic 

The total electric force/eietuic acting on the chiral nematic layers is 

as was shown for the magnetic case (see Eq. 124), the threshold field, E, is proportional to pd). For long pitch systems and thick cells, these effects are readily observed [156-159] in moderate electric fields ( a few volts/micrometers) and this analysis has been extended to the general case of ac fields [134] to give 

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