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当外磁场强度比较小时,液晶不会发生Freedericksz转变。利用介电张量分析了扭曲型向列液晶在弱磁场中的旋光效应。通过理论分析表明,线性偏振光经过磁场中的扭曲型向列液晶,会产生左右两束椭圆偏振光。这两束椭圆偏振光在该液晶中的传播速度不同,导致光经过液晶盒后光电场振动面发生偏转。进一步分析表明,对于同一种波长的光,磁场强度越大,其电场振动面旋转角度越大。在相同的磁场强度下,光波长越短,其电场振动面旋转角度越大。如果加上高的偏置电压,使向列型液晶分子长轴方向与外磁场方向平行,线性偏振光经过磁场中的该扭曲型向列液晶,其振动面会也发生偏转。
When the external magnetic field intensity is relatively small, the Freedericksz transition does not occur in the liquid crystal. The optical rotation effect of twisted nematic liquid crystal in weak magnetic field was analyzed by dielectric tensor. Theoretical analysis shows that the linearly polarized light passes through the twisted nematic liquid crystal in the magnetic field and will generate two elliptically polarized beams on the left and the right. The propagation speed of the two elliptically polarized lights in the liquid crystal is different, resulting in deflection of the vibration field of the photoelectric field after passing the liquid crystal cell. Further analysis shows that for the same wavelength of light, the greater the magnetic field strength, the greater the angle of rotation of the electric field vibration plane. Under the same magnetic field intensity, the shorter the light wavelength, the larger the rotation angle of the electric field vibration plane. If a high bias voltage is applied so that the long axis direction of the nematic liquid crystal molecules is parallel to the direction of the external magnetic field, the linearly polarized light passes through the twisted nematic liquid crystal in the magnetic field to deflect the vibrating surface.