Preparation of Twist Cells, Optical Properties at Zero Field

1 Preparation of Twist Cells, Optical Properties at Zero Field 

A twist cell is usually formed by placing orienting glasses on top of each other. Then twist directions at angles tt/2 and —tt/2 are equally probable. Regions with different signs of twist are observable by interference methods 

FIGURE 4.12. Variation with voltage of the optical characteristics of twist cells between parallel polaroids d = 30 /xm, a mixtiure of nematic liquid crystal with Ae = +0.22, T = 23 C) [66]. (1) Transmission with a cell conventionally arranged to the polarization of the incident ray (2) transmission when the cell is rotated around the normal through 45 from the original position (3) phase lag calculated from curve 2. Axes to the right and bottom refer to (1) and (2) and axes to the left and top refer to (3). 

A nonzero tilt of the molecules to the cell surface Oq also results in a nonuniform twisting. In [71], it is suggested that the construction of twist cells with a certain pretilt angle will also eliminate the walls. 

As seen from Fig. 4.13 the Maiguin conditions at the output of the twist cell 

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