Observation of dynamic behavior of enhanced optical Kerr effect in light-absorbing liquid.

We observed the dynamic behavior of the optical Kerr phenomenon in the isotropic phase of the liquid crystal, enhanced by the doping of the light-absorbing dye molecules. The system is regarded as a candidate of the Brownian motor, and the newly developed polarization modulation Kerr spectroscopy technique was successfully applied for the light-absorbing sample: The frequency spectra of the molecular orientation were obtained in the vicinity of the isotropic-nematic phase transition temperature. We examined the relaxation behavior as a function of the dye concentration giving the number of liquid crystal molecules dominated by a dye, and the temperature determining the size of the quasidomain of the molecular orientation. The result shows that the critical slowing down of the relaxation is not affected by the dopant, though the magnitude of Kerr constant drastically increases. It is also shown that the change in the elastic coherence length does not affect the enhancement phenomenon. This gives evidence for the idea of the Brownian motor as the mechanism of the enhanced optical Kerr effect.