NONLINEAR ELECTROOPTICAL SPECTRA OF FREE STANDING FILMS OF FERRO AND ANTIFERROELECTRIC LIQUID CRYSTALS

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As a response to external field easily becomes nonlinear in soft condensed matters such as liquid crystals, we have developed the measurement system of nonlinear electrooptical relaxation spectrum in a frequency domain as a new method to obtain the information on the structure and dynamics of liquid crystals. In our system, by using a sinusoidal electric field as an input, we can detect nonlinear responses separately as respective higher harmonic components of fundamental frequency. We can also obtain the information on anisotropy in electrical and optical properties of liquid crystals and distinguish the forms of interaction between electric field and liquid crystals by their higher harmonic responses.We have applied the developed system to ferroelectric liquid crystals (FLCs) in the SmC* phase and antiferroelectric liquid crystals (AFLCs) in SmCィイD2AィエD2* Phase. The measured linear and nonlinear spectra are found to make good agreement with those calculated theoretically. By analysis of measured spectra with the theoretically calculated ones, we have obtained useful information on the dynamics of FLCs and AFLCs. Especially in AFLCs, we have succeeded in measurement of the antiferrroelectric Goldstone mode by second-order nonlinear spectrum, but no relaxation behavior has been observed in the linear spectrum.We have also applied the developed system to free standing films of FLCs with various thickness. In films thicker than the pitch of helical structure, the new relaxation mode whose relaxation frequency depends on thickness of film has been found other than Gold-stone mode as is also observed for FLCs in cells. By varying temperature, thickness of a film and applied electric field, we have obtained the new information on the dynamics of FLCs confined in a quasi-two dimensional system.