title: Imaging colloidal particle induced topological defects in a nematic liquid crystal using third harmonic generation microscopy.
abstract: The nature of the third-harmonic generation (THG) process in a nematic liquid crystal is investigated for the case of tightly focused, low intensity, laser beams. Colloidal particle induced topological defects in a liquid crystal are visualized in three-dimensions using the dependence of the THG signal on both changes in non-linear susceptibility and the orientation of the liquid crystal director relative to the incident laser polarization state. We have found that the interpretation of THG images in a liquid crystal is complicated not only by the change in polarisation of the electric field as it propagates through the medium but also by anisotropic refractive index mismatch induced aberrations.
authors.forename: Rajesh S
authors.initials: RS
authors.lastname: Pillai
authors.forename: Masahito
authors.initials: M
authors.lastname: Oh-E
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yokoyama
authors.forename: G J
authors.initials: GJ
authors.lastname: Brakenhoff
authors.forename: Michiel
authors.initials: M
authors.lastname: Müller