Complex Strain-Optical Coefficient Measurements by Means of Polarization Analysis of a Diffracted Light by Longitudinal Ultrasound

概要

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The theory to obtain the complex strain-optical coefficients was described for the liquids from polarization analysis of a diffracted light by longitudinal ultrasound. The polarization analyses on the isotropic phase of liquid crystal, 4-cyano-4-pentylbiphenyl (5CB) were carried out at 40, 50 and 60 °C in the frequency range from 5 to 25 MHz.For the +1st and -1st order diffracted lights, values of change in arc tangent of the ratio of electric field and the phase retardation between two polarizations were obtained as functions of square of the Raman-Nath parameter.From intercepts of those values, the complex strain-optical parameters were determined.The frequency dependences of the complex strain-optical parameters at 40, 50 and 60 °C were obtained and compared with those calculated by using the data of using the reorientational relaxation frequency and the flow birefringence per unit strain rate. Although some discrepancies are found at 40 and 50 °C, the results indicate applicability the proposed method to determine the strain-optical coefficients above MHz range.