A model is presented for computing the conoscopic figures produced by a uniformly oriented liquid crystal (LC) in a thin cell observed with a polarizing microscope. The method takes account of refraction and primary reflection at each interface within the cell but neglects multiple reflections. It is shown that the form of the isochromes in the figures is given qualitatively by the intersections of Bertin's surfaces with the LC surface but that refraction also influences the form of the isochromes. Examples of calculated conoscopic figures are presented, including the symmetric flash figure and the optic-normal figure. The way in which these are altered by small changes in the optic-axis orientation is demonstrated. To complete the model, the polarizing effect of the microscope condenser and objective lens systems is estimated by calculating the Fresnel coefficients for model lens systems; the effect on the conoscopic figures is noted. Finally the director tilt in a 7-μm chiral smectic C LC cell is determined by comparing an experimentally measured figure with a set of calculated figures.

© 1990 Optical Society of America

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