CARS polarized microscopy of three-dimensional director structures in liquid crystals.pdfVIP

1 CARS polarized microscopy of three-dimensional director structures in liquid crystals A.V. Kachynski 1 , A.N. Kuzmin 1 , P.N. Prasad 1,a , and I.I. Smalyukh 2,b 1 The Institute for Lasers, Photonics, and Biophotonics, University at Buffalo, The State University of New York, Buffalo, NY 14260, USA 2 Department of Physics and Liquid Crystal Materials Research Center, University of Colorado at Boulder, Boulder, CO 80309, USA We demonstrate three-dimensional vibrational imaging of director structures in liquid crystals using coherent anti-Stokes Raman scattering (CARS) polarized microscopy. Spatial mapping of the structures is based on sensitivity of a polarized CARS signal to orientation of anisotropic molecules in liquid crystals. As an example, we study structures in a smectic material and demonstrate that single-scan CARS and two-photon fluorescence images of molecular orientation patterns are consistent with each other and with the structure model. Long-range orientational order is an important property of liquid crystals (LCs) [1]. Local average molecular orientations are described by the director nn ?? ?≡ , which is an optical axis in the uniaxial LC materials. Non-invasive imaging of the three-dimensional (3-D) spatial patterns of )(? rn r is important for fundamental LC research and for a broad range of technological applications. Fluorescence Confocal Polarizing Microscopy (FCPM) [2] visualizes 3-D director fields by taking advantage of (a) doping anisometric dyes that homogeneously distribute and align in the LC and (b) polarized excitation and fluorescence detection. In this approach, the absorption/emission transition dipoles of elongated dye molecules follow )(? rn r and the polarized confocal imaging visualizes the 3-D director patterns [2]. However, this approach requires doping a specially selected dye that at small concentrations would provide strong contrast without affecting the LC properties. The labeling-free