Accurate interferometric method for the measurement of electro-optic coefficients: application to a single β-barium borate crystal

Abstract

A modified interferometric technique is shown to be able to determine even the small values of electro-optic (EO) coefficients with good accuracy. The experimental setup is a Michelson interferometer that includes an EO modulator in one arm and the crystal under study in the other arm. The method is based on the measurement of the reference modulator phase shift to compensate the phase shift induced by a dc field in the crystal under study. An original technique of detection ensures a better sensitivity since a refractive-index change of 10-7 and an optical path-length variation of λ/1000 can be achieved. The relative sign of EO coefficients, the change of the sample dimensions owing to the piezoelectric effect, and the influence of the temperature are successively discussed. The technique was applied to determine some EO coefficients of a standard lithium niobate crystal and all components of the EO tensor in a β-barium borate crystal.