It is well known that the photorefractive effect in lithium niobate almost vanishes doping with Mg, Zn, or In, giving the opportunity of taking advantage of its oscillator-type nonlinear optical properties useful in applications such as second harmonic generation, self- focusing, optical bistability, etc.
In this work, direct measurements of photoconductivity coefficients and photorefractive gains at cw 532 nm for six LiNbO3 samples at two c-axis orientations with different Mg content levels have been obtained. A direct relationship between the increase of photoconductivity and the photorefractive inhibition was not observed. In addition, only a slight influence of photoconductivity on holographic erasure time of diffraction gratings has also been found. An explanation for these unexpected results considering the distribution of magnesium ions with respect to polar axis is proposed.