Pitch determn. for cholesteric liq. crystal - using laser beam for passing through wedge cell on detector array

摘要

The pitch of cholesteric liq. crystals is determined by appts including a wedge cell with a cholesteric liquid crystal having a Grandjean texture and a source of light to produce a multi-reflection pattern of the empty cell. A diffraction pattern is produced on the disclination lines of the cholesteric liquid crystal. The appts comprises an He-Ne laser (1) and a wedge cell (2), partly filled with the cholesteric liquid crystal (4) leaving an air gap (3). The wedge angle (5) could be 1.15 deg. The detector (6) is an array of photodiodes or photomulti-pliers. The multireflection and/or diffraction pattern (7,8) is of measuring taken by altering the distance (9) of the detector array. ADVANTAGE: This method is capable the length of pitch(p) in a wide range of up to more than 100 mu with a high precision.