Optical Reorientation and Trapping of Nematic Liquid Crystals Leading to the Formation of Micrometer-Sized Domain

摘要

We report on observation of optical reorientation of homogeneous nematic liquid crystals (LCs) thin slab of 4'-penthyl-4-cyanobiphenyl induced by a tightly focused near-infrared laser beam. We found that for laser beam with intensity higher than 56 MW/cm~2 the optical reorientation unusually transforms to a new metastable domain, which grows with laser irradiation time up to a dimension much larger than that of the focal spot. The optically reoriented LCs with refractive index mismatch compared to the surroundings can act as a micrometer-sized "ghost particle", leading to the generation of optical trapping and manipulation of the optically reoriented LCs. By using confocal Raman microspectroscopy, we show that the dichroic ratio in the confined focal volume changes upon the domain formation with an increase in the total Raman intensity, indicating that microscopic depolarization leading to deorientation or nematic → isotropic phase transition and possible microscopic densification takes place by the tightly focused laser beam.