DEVEROPEMENT OF NONLINEAR RELAXATION SPECTROMETER IN A FREQUENCY DOMAIN

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As a response to external field easily becomes nonlinear in soft condensed matters such as polymers and liquid crystals, the nonlinear relaxation spectroscopy is an useful method to investigate the dynamics of these matters. We have developed the nonlinear relaxation spectrometer in a frequency domain using a sinusoidal electric field as an input. In our system, harmonic distortion of the applied electric field has been removed by low-pass filter and the nonlinear responses have been extracted from response signals after cancel of the fundamental component by the digital balancing method. The digital balancing method makes it possible to measure the nonlinear spectra with high accuracy free from the dynamic range of the spectrometer.We have applied the developed system to ferroelectric liquid crystals in the SmC^* phase and checked the usefulness of the system. The measured linear and third-order nonlinear spectra are found to make good agreement with those calculated theoretically. We have succeeded in the evaluation of the material constants which are important in the display application such as spontaneous polarization and rotational viscosity by the comparison between those two spectra.We have also applied that system to the nonlinear electrooptic measurement, in which the intensity of the transmitted intensity through cells filled with ferroelectric liquid crystals is detected as an output signal. It is found the odd harmonic spectra offer the similar information to that obtained from the nonlinear dielectric spectra and the even harmonic spectra offer the information on the electric and optical anisotropy of liquid crystals.In conclusion, we have developed new nonlinear relaxation spectrometer and showed the usefulness of the system in the study of dynamics of liquid crystals.