Crystalline perfection, EPR, prism coupler and UV-VIS-NIR studies on Cz-grown Fe-doped LiNbO3: A photorefractive nonlinear optical crystal

Abstract

The Fe-doped (0.05 mol%) lithium niobate (LiNbO₃) bulk single crystal was gown by the Czochralski (Cz) method using a co-axial two zone low thermal gradient furnace. The crystalline perfection of the grown crystal was evaluated by high resolution X-ray diffractometry which showed that it does not contain any structural grain boundaries, and the dopants predominantly occupied vacancy sites of Li⁺ in the lattice. Electron paramagnetic resonance studies revealed the incorporation of Fe³⁺ ions at Li sites. The Z-cut optically polished 450 μm thick wafer was used for birefringence measurements on a prism coupler spectrometer with 632.8 nm wavelength and it was found that the difference in refractive index (Δn) for ordinary and extraordinary rays is 0.0833. The optical transmission/absorption spectra were studied by UV-VIS-NIR spectroscopy and this showed that the grown crystal has good optical sensitivity for 482 nm wavelength radiation. The present studies reveal that the crystal grown with a two zone low thermal gradient furnace has very good device properties which are needed for holographic data storage applications.