Lithium tantalate crystals of compositions ranging from 48.3 mol % to 50.0 mol % lithium oxide are fabricated by vapor transport equilibration. Light-induced refractive index changes of the crystals are investigated with holographic methods at usual cw-laser intensities (≈ 105 W/m 2) and with a single focused laser beam at high light intensities up to 2 × 107 W/m2. In stoichiometric crystals the index changes are reduced by more than two orders of magnitude when compared with congruently melting ones. Simultaneously, the normalized photoconductivity σph/I, where I is the light intensity, increases by nearly two orders of magnitude. Therefore, stoichiometric lithium tantalate is an attractive material for applications such as frequency conversion via quasi-phase matching. © 2004 American Institute of Physics.