Tight focusing of laser light using microlens array combined with radially polarised light converter

A facile method to prepare a liquid crystal polarisation conversion microlens array (LCPC MLA) is reported. One-step photolithography was used to form a microhole array patterned fluoropolymer poly (butenyl vinyl ether) (CYTOP) layer on the front and back side of a thin glass substrate. On the front side, LC droplets are radially aligned in the microholes, and a twisted radial arrangement texture is formed by the integration of another glass substrate coated with a parallel alignment layer to create the LCPC array. The MLA is located at the rear side of the thin glass substrate and each microlens centre is completely aligned with the centres of the LC droplets in the LCPC array. The LCPC array can convert linearly polarised light to radially polarised light and the MLA can focus the radially polarised light to a spot array. This tightly focused array has a high intensity and at each focused spot, a large component of the electric field is in the longitudinal direction. The LCPC MLA has a compact structure, good stability, and highly uniformity, and it shows potential for applications such as material processing, phase modulation, polarisation compensation, and polarisation imaging.

本研究报道了一种制备液晶偏振转换微透镜阵列（liquid crystal polarisation conversion microlens array, LCPC MLA）的简便方法。采用一步光刻法在薄玻璃基板的正反两面制备出图案化微孔阵列的氟聚合物聚(丁烯基乙烯基醚)(CYTOP)层。在基板正面，液晶液滴在微孔内呈径向排列；通过与另一层涂覆有平行取向层的玻璃基板贴合，形成扭曲径向排列织构，进而制备得到LCPC阵列。微透镜阵列位于薄玻璃基板的背面，且每个微透镜的中心与LCPC阵列中液晶液滴的中心完全对齐。LCPC阵列可将线偏振光转换为径向偏振光，而微透镜阵列可将径向偏振光聚焦为点阵光斑。该紧聚焦点阵具有较高的光强，且每个聚焦光斑的电场中存在较大的纵向分量。所制备的LCPC MLA结构紧凑、稳定性优异且高度均匀，在材料加工、相位调制、偏振补偿及偏振成像等领域具有应用潜力。