Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University, Kent, Ohio 44242, USA.
Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433, USA.
Nature. 2016 Mar 17;531(7594):352-6. doi: 10.1038/nature17141. Epub 2016 Mar 7.
Chiral nematic liquid crystals--otherwise referred to as cholesteric liquid crystals (CLCs)--are self-organized helical superstructures that find practical application in, for example, thermography, reflective displays, tuneable colour filters and mirrorless lasing. Dynamic, remote and three-dimensional control over the helical axis of CLCs is desirable, but challenging. For example, the orientation of the helical axis relative to the substrate can be changed from perpendicular to parallel by applying an alternating-current electric field, by changing the anchoring conditions of the substrate, or by altering the topography of the substrate's surface; separately, in-plane rotation of the helical axis parallel to the substrate can be driven by a direct-current field. Here we report three-dimensional manipulation of the helical axis of a CLC, together with inversion of its handedness, achieved solely with a light stimulus. We use this technique to carry out light-activated, wide-area, reversible two-dimensional beam steering--previously accomplished using complex integrated systems and optical phased arrays. During the three-dimensional manipulation by light, the helical axis undergoes, in sequence, a reversible transition from perpendicular to parallel, followed by in-plane rotation on the substrate surface. Such reversible manipulation depends on experimental parameters such as cell thickness, surface anchoring condition, and pitch length. Because there is no thermal relaxation, the system can be driven either forwards or backwards from any light-activated intermediate state. We also describe reversible photocontrol between a two-dimensional diffraction state, a one-dimensional diffraction state and a diffraction 'off' state in a bilayer cell.
手性向列液晶——也被称为胆甾相液晶 (CLC)——是自组装的螺旋超结构，在热成像、反射式显示器、可调谐滤色片和无镜激光等方面具有实际应用。理想情况下，希望能够对手性向列液晶的螺旋轴进行动态、远程和三维控制，但这具有挑战性。例如，通过施加交流电场、改变基底的锚定条件或改变基底表面的形貌，可以将螺旋轴相对于基底的取向从垂直变为平行；另外，通过直流场可以驱动平行于基底的螺旋轴的面内旋转。在这里，我们报告了仅通过光刺激对手性向列液晶的螺旋轴进行三维操纵，以及其手性的反转。我们使用这项技术实现了光激活的、大面积的、可逆的二维光束转向——以前需要使用复杂的集成系统和相控阵光学来实现。在光的三维操纵过程中，螺旋轴依次经历从垂直到平行的可逆转变，然后在基底表面上进行面内旋转。这种可逆操纵取决于细胞厚度、表面锚定条件和螺距长度等实验参数。由于没有热弛豫，系统可以从任何光激活的中间状态向前或向后驱动。我们还描述了在双层单元中，二维衍射态、一维衍射态和衍射“关闭”态之间的可逆光控。
