Laser Induced Kerr effect spectroscopy

凝胶、乳液和生物系统等复杂流体作为新型功能材料可应用于各个行业，因此引起了物理学家的极大兴趣。复杂流体的特性可归因于它们的大自由度，如分子构象和缔合。分子取向是形成液晶相的重要顺序之一，对液晶相的形成起着重要的作用。本研究的目的是建立一种在宽频率范围内观察液体材料取向分子动力学的新实验系统。我们成功地开发了连续波激光器的光学克尔效应光谱技术。分子的各向异性形状必然伴随着各向异性介电性。偏振激光束的电场诱导分子取向，用光学椭偏仪测量分子取向的克尔效应。在向列各向同性相变温度附近观察到线虫的临界现象。对该系统进行了改进，用于观察分子旋转的动态过程。采用宽带电源驱动波克尔斯电池，实现了激光偏振的高频控制。复响应函数的精确测量为液晶的相变和分子动力学提供了重要的信息。我们首次在不同种类液晶的频域中观察到光学克尔效应的弛豫。激光诱导分子取向技术将成为研究液晶相变机理的有力工具。

Complex fluids such as gels, emulsions and bio-systems attract a great physical interest since they could be applied for various industries as new functional materials. The characteristic properties of the complex fluids can be attributed to their large degree of freedom, such as molecular conformation and association. The molecular orientation is one of the important orders, which plays a significant role in creating the liquid crystal phase. The purpose of the study is to develop a new experimental system for observing the orientational molecular dynamics of liquid materials in a wide frequency range.We successfully developed the optical Kerr effect spectroscopy technique with a continuous wave laser. The anisotropic shape of the molecule necessarily accompanies the anistropic dielectricity. The electric field of the polarized laser beam induces the molecular orientation, which is measured by the optical ellipsometry as the Kerr effect. The critical phenomenon was observed for the nematogen near the nematic-isotropic phase transition temperature. The system was improved to observe the dynamic process of molecule rotation. The Pockels cell was driven with a wide band power supply for the high frequency control of the laser polarization. The complex response function was accurately measured, which gives us an important information on the phase transition and the molecular dynamics of liquid crystals. We observed the relaxation of the optical Kerr effect for the first time in the frequency domain in various kinds of liquid crystals. The laser induced molecular orientation technique would be a powerful tool for the investigation of the mechanism of phase transition of liquid crystals.