弱磁场中向列相液晶的磁光效应

Magnetic-Optics Effect of Nematic Liquid Crystal in Weak Magnetic Field

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。

The structure of twisted namatic liquid crystal does not change under weak magnetic field. The rotation of polarization of light in the twisted nematic liquid crystal with the applied weak magnetic field is analyzed using the dielectric rate tensor. The theoretical results show that linearly polarized light transmitting this liquid crystal can produce left-hand and right-hand elliptically polarized light, which corresponds to the different speed of propagation. This leads to the rotation of polarization of light when it passes through this liquid crystal. A method to calculate rotation angle which results from the combination of the left-hand and right-hand elliptically polarized light is given. The dependence of the transmitted ratio of light on the applied magnetic field is founded. Under the same wavelength of light, the more intense the magnetic field strength, the larger the rotated angle of polarization of light. At the same magnetic field strength, The shorter the wavelength of light, the larger the rotated angle of polarization of light. When the directors of liquid crystal are parallel to the direction of the magnetic field, the polarization rotation of light can also been observed.