Electro-optical properties of near-stoichiometric and congruent lithium tantalate at ultraviolet wavelengths

We measured the unclamped electro-optic coefficients r13 and r33 of near-stoichiometric and congruent lithium tantalate (LiTaO3) from lambda=633 nm down to the absorption edge at ~275 nm. Electro-optical coefficients up to r33=52+/-1 pm/V have been determined at lambda=275 nm. The reduced half-wave voltage at 275 nm is vpi=300+/-10 V for r33 and vpi=560+/-20 V for the configuration employing rc=r33−(no/ne)3r13. We propose a two-oscillator polarization potential model that well describes our data in the UV. In the investigated wavelength range the values for stoichiometric and congruent LiTaO3 differ by less than 3%, which is below the accuracy of our measurements. In addition, the refractive indices in the UV were measured, and more precise Sellmeier parameters for the UV and visible were determined based on the previous and new refractive-index data.