The study of Fresnel lens in twisted-nematic liquid crystal fabricated by Sagnac interferometer

• Main Authors: Tian-yi Jhuang, 莊田易
• Other Authors: Chie-tong Kuo
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/32qyse

碩士 === 國立中山大學 === 物理學系研究所 === 105 === This study presents a focusing efficiency and focal length tunable Fresnel lens with liquid crystals fabricated by a Sagnac interferometer. When the Fresnel-pattern green beam, formed by the Sagnac interferometer, is irradiated on the azo-dye doped liquid-crystal mixture, the azo-dye molecules will undergo the trans-cis photoisomerization and then generate photo-alignment effect in the bright (odd) zone, which results that the direction of liquid-crystal molecules will perpendicular to the linearly polarized pump beam. The various structures of liquid crystals in the odd and even zones will produce the phase difference, resulting in a Fresnel lens generated. The focusing efficiency of proposed Fresnel lens can be controlled by the external AC voltages. The experimental results show that the focusing efficiency can reach its maximum of 31.5 % under applied voltage of 3.1 V. In addition, the photo-alignment effect of azo dyes can be erased through the thermally method and rewritten by the pump beam with different Fresnel-like pattern, which leads to the Fresnel lens with various focal lengths.