Measurement of electro-optic properties

In their ferroelectric state, the electro-optically useful PLZT compositions have an almost cubic structure, with the polar c axis being typically only about 1% longer than the a axes. Consequently the optical properties are almost isotropic and this, in part, is why high transparency can be achieved in the ceramic form. When an electric field is applied to the ceramic, domain alignment, or a field-enforced transition to the ferroelectric state, leads to the development of macroscopic polarization and so to uniaxial optical properties, i.e. the optic axis 

The birefringence is measured using apparatus of the type shown in Fig. 8.10(a). He-Ne laser light (/. = 0.633 /mi) is passed through the polarizer P, and then through the electroded specimen. The specimen is in the form of a polished plate, of thickness t typically 250 /mi, carrying gold electrodes with a gap of approximately 1mm. 

The Babinet compensator is a calibrated optical device comprising two wedge-shaped pieces of quartz arranged so that their optic axes, and the light path, are 

An expression is now derived for the light intensity transmitted by P2 in the case where the relative retardation introduced by the specimen is T and the compensator is removed. It is helpful to refer to Fig. 8.10(b) which represents the system viewed from the photodiode. If the amplitude transmitted by the polarizer P, is a sin(cot), then the. v and y components incident on the PLZT are 

On passing through the uniaxial negative PLZT the x component is retarded by an angle S = (T/2)2n, where T = tAn. The amplitude aT transmitted by P2 is 

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