Photorefractivity of zirconium-doped lithium niobate

In this work we study the photorefractive and electro-optical properties of Zirconium-doped congruent lithium niobate (LN) crystals. In order to set the ground for the utilization of these crystals in nonlinear wavelengthconversion devices, we investigate the dependence of the photorefractive properties of the crystals on dopant concentration and incident power. In our experiments the birefringence variations induced by a 532-nm laser beam are measured by using the Sénarmont method, in the ZrO2 concentration range 0-3mol% and intensity range 155- 1800 W/cm2. In order to investigate photorefractivity at high intensities, we have also utilized the direct observation of the distortion of the light spot transmitted by the crystal. In presence of photorefractivity, the transmitted light spot becomes smeared and elongated along the c-axis. Our data show that the threshold ZrO2 concentration can be in the range 2.5-3mol%. Considering that the growth of large homogeneous Zr:LN crystals should be easier than for Mg:LN, and that electrical poling of these crystals has already been demonstrated, Zr-doped LN could represent a more convenient choice than Mg:LN for the realization of room-temperature wavelength converters.