Experimental determination of effective electro-optic coefficient and electric screening field factor in the electrically induced birefringent Bi12TiO20 crystal by using an oblique incidence setup

We present an alternative procedure to determine the effective electro-optic coefficient (reff) and the electric screening field factor by measuring the optical intensity variation induced by an applied electric field (EApp), which is transmitted through an undoped photorefractive Bi12TiO20 (BTO) crystal in an oblique incidence setup. The transmitted intensity variation (TIV) was modeled taking into account the transmission coefficients for the polarization plane parallel and perpendicular to the incidence plane, as well as the birefringence induced by the EApp, which changes the components of the polarization vector of the light beam. The measurements were performed with infrared radiation at 780 nm and provided reff=5.5±0.2 pm/V. It allowed us to conclude, with support of results from the literature, that the region without dispersion of the electro-optic coefficient in the BTO crystal ranges from 510 nm to at least 780 nm. The procedure proposed here can be used for distinct wavelengths and seems to be suitable for other electrically induced birefringent materials.