Optical properties of nematic microlenses doped with chiral nanoparticles
Optical properties of nematic microlenses doped with chiral nanoparticles
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DOI：
10.1117/12.2568570
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发表时间：
2020-08
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影响因子：
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通讯作者：
Kelum Perera;Alham Nemati;E. Mann;T. Hegmann;A. Jákli
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文献类型：
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作者：
Kelum Perera;Alham Nemati;E. Mann;T. Hegmann;A. Jákli
非手性分子的向列液晶或手性分子的外消旋混合物在悬浮于亚毫米大小的网格中并浸入水中时，在圆偏振片之间形成扁平薄膜并显示均匀的纹理。最近的研究表明，在液晶中加入手性掺杂剂后，薄膜呈现出双折射颜色径向变化的同心环形光学结构，同时薄膜呈现双凸结构。弯曲的形状加上简并的平面锚定导致光轴沿薄膜平面的径向变化，提供了主导成像的Pancharatnam-Berry型相位透镜。本文描述了加入手性纳米粒子形成的向列型液晶微透镜的初步结果。结果表明，纳米颗粒的螺旋扭转力比最强分子手性掺杂剂的螺旋扭转力大一个数量级。从我们在这里提出的观察，我们能够估计形状和透镜的几何焦距，并证明其性能作为一个光学器件。使用手性纳米粒子制造微透镜可以通过纳米粒子吸收的光来调节，或者对于磁性纳米粒子，可以通过磁场来调节。此外，在已知NP浓度下的焦距测量为测量手性纳米颗粒的螺旋扭转力提供了一种新的方法。
Nematic liquid crystals of achiral molecules or racemic mixtures of chiral ones form flat films and show uniform textures between circular polarizers when suspended in sub-millimeter size grids and submersed under water. Recently it was shown that on addition of chiral dopants to the liquid crystal, the films exhibit optical textures with concentric ring patterns with radial variation of the birefringence color, while the films become biconvex. The curved shape together with degenerate planar anchoring leads to a radial variation of the optical axis along the plane of the film, providing a Pancharatnam-Berry type phase lens that dominates the imaging. Here we describe preliminary results of nematic liquid crystal microlenses formed by the addition of chiral nanoparticles. It is found that the helical twisting power of the nanoparticles, the key factor to form the lens, is an order of magnitude greater than that of the strongest molecular chiral dopants. From the observations we present here, we were able to estimate the shape and the geometric focal length of the lens and demonstrated its performance as an optical device. The use of chiral nanoparticles to make microlenses may allow tuning by light that the nanoparticles absorb or, for magnetic NPs, by magnetic fields. Further, the measurement of focal length at known NP concentration offers a new method to measure the helical twisting power of chiral nanoparticles.