Influences of Fe3+ ions on rapid growth and laser-induced nonlinear refraction of potassium dihydrogen phosphate crystal

For rapidly grown KDP crystal, the whole growth zone is composed of prismatic- and pyramidal-sector. In order to further understand the distinctions between them, KDP crystals doped with Fe3+ in trace amount were selected to explore the influences of metal cation with high-valence on growth characteristics, Optical quality and nonlinear refraction. The growth characteristics for as-grown crystals indicate that the growth rate of prismatic sector can be obviously inhibited by Fe3+ ions with less than 15 ppm due to the stronger electronegativity of (100) face. With the increase of Fe3+, the crystal and optical qualities show significantly lower trends, especially for the prismatic sector. The influence of Fe3+ ions on nonlinear refraction was observed by Z-scan technique, which shows that self-focusing effect could be caused in high-intensity laser system because of the nonlinear refractive index obtained with a positive sign. Specially, nonlinear refraction effects along II-type and z-cut in prismatic area both show a significant variation with increase of Fe3+, while a negligible effect on nonlinear refraction is proved for pyramidal sector. Additionally, the generation of nonlinear refraction is mainly attributed to the electron-cloud distortion of H2PO4- groups, and the changes in prismatic sector may be due to the existence of (FeO4)(2-) groups.