All optically generated, relocatable umbilic defects in a liquid crystal (LC) with positive dielectric anisotropy are reported. The studied samples are made with a Fe-doped LiNbO₃ substrate showing the bulk photovoltaic effect and an ITO coated glass plate as covering substrate. Umbilics are created upon exposure with a focused laser beam: They are induced via photo generated fields at the relocatable exposure beam position. The field distribution of these fields is normal to the sample plane at the exposure spot center and has increasingly high in-plane field components in radial direction: Ideal conditions to induce director reorientations with radial symmetry in a LC with positive dielectric anisotropy. The irradiated regions are studied with polarized probe light revealing the patterns characteristic for umbilic defects and the typical doughnut-shaped intensity distributions expected for optical vortex beams. The experimental findings are compared to calculated transmission profiles. Moreover, a LC with negative dielectric anisotropy was studied in the same type of sample for reference.

报告了具有正介电各向异性的液晶（LC）中所有光学产生的可重定位脐带缺陷。研究的样品由掺铁的LiNbO ₃制成衬底显示出整体光伏效应，并用ITO涂覆的玻璃板作为覆盖衬底。脐带是在聚焦激光束曝光后产生的：它们是通过可重定位曝光束位置处的光生场感应出来的。这些场的场分布在曝光点中心处垂直于样品平面，并且在径向方向上具有越来越高的平面内场分量：在具有正介电各向异性的LC中以径向对称性诱导指向矢重取向的理想条件。用偏振探测光研究辐照区域，揭示了脐带缺陷的图案特征和光学涡旋光束所期望的典型的甜甜圈状强度分布。将实验结果与计算出的透射曲线进行比较。此外，