Ellipsometric investigation of the electro-optic and electrostrictive effects in anodic Ta 2 O 5 films

Abstract
A computer-controlled ellipsometer was used to detect and measure the increase in thickness, the decrease in refractive index and the development of birefringence which occur on applying fields up to a few hundred MV m‒1 to anodic oxide films made in dilute sulphuric acid on tantalum. The films were shown to be optically isotropic and homogeneous at zero field but to be optically anisotropic with field applied. There is a rapid change in index and thickness when a field is first applied, followed by a slower change with relaxation time of the order of 10 s. Both the index and the thickness changes are quadratic in the field, as is to be expected for a material which is isotropic with no field applied.

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