  We report the optical and dielectric properties in hafnium (Hf)-doped lithium
niobate (LN) crystals. We investigated samples of congruent composition with
various doping concentration varying from 0 to 8 mol%. The clamped and
unclamped values of the electro-optic coefficient r 22 of Hf-doped LN and the
corresponding dielectric permittivity as well, have been experimentally
determined and compared with the results obtained in undoped congruent LN
crystals. We show that the electro-optic and dielectric properties are only
slightly affected by the introduction of hafnium ions, and therefore Hf-doped
LN has the advantage of low photorefractive damage compared with the undoped
congruent LN.
