Direct measurement of the dispersion of the electrogyration coefficientof photorefractive Bi 12 Ge O 20 crystals

We report on the direct measurement of the electrogyration coefficient of Bi 12 Ge O 20 sillenite crystals over the visible spectral range. The coefficient is directly measured on a (111)-cut crystal for which the electro-optic and electrogyratory effects are decoupled. The precision of the measurement method over various parameters including absorption and misorientation is examined. The value of the electrogyration coefficient is found to vary from 0.37 ± 0.03 to 0.05 ± 0.01 pm ∕ V for the 460 - 760 - nm spectrum range, which is within the upper boundaries that have been specified in previous experiments. It is also found that the electrogyration coefficient follows the dispersion law of optical activity and refractive index.