Focused Laser Heating Induced Local Reorientations of Chiral Nematic Liquid Crystals
Chih-Hsiang Kuo1, Jia-De Lin1*
1Department of Opto-Electronic Enginering, National Dong Hwa University, Hualien, Taiwan
* Presenter:Jia-De Lin, email:jdlin1218@gms.ndhu.edu.tw
This study investigates the photothermal effect of indium tin oxide (ITO) and its impact on the molecular arrangements of chiral nematic liquid crystal (N*LC) samples. When N*LC sandwiched between ITO glass substrates are irradiated by a Gaussian beam from optical tweezers, the laser light induces localized heating in the ITO layer, creating point heat sources within the N*LC sample that further influence the orientations of the N*LC molecules. If the laser power is sufficient, the sample can be locally heated to the phase transition temperature and form isotropic islands. The threshold laser power for forming isotropic islands is inversely related to the sample thickness. In contrast, the area of the isotropic islands is directly related to the laser power of the optical tweezers. Upon turning off the laser, the isotropic islands in N*LC samples with homogeneous alignment treatment will spontaneously return to the planar state with the aid of the anchoring forces from the surface boundaries. Consequently, defect structures with the topological charge of zero, such as oily streaks and focal conic domains within the planar N*LC samples, can be locally annealed and eliminated by generating and then removing the isotropic islands over there. In contrast, N*LC samples with hybrid alignment treatment leave long-lasting focal conic states where the isotropic islands were generated. The demonstrations shown in this work could have a high potential for the developments of high-quality reflective color filters and colorful boogie boards.


Keywords: optical tweezers, liquid crystals, chirality, defects, local heating