Laser Induced Kerr effect spectroscopy

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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.