Domain Structure Studies in Phases of Bent-Shaped Molecules by Spatially Resolved Second Harmonic Microscopy

Abstract

This article arrived too late to be included in the appropriate section of the ILCC Proceedings, which is Structural Characterization.Several banana-shaped liquid crystalline molecules have been studied as active media for second harmonic generation (SHG) in their different thermotropic phases [1]. Besides the B 2 -and B 7 -phases, which exhibit SHG under external applied electric fields, the so-called ''blue'' B 4 -phase exhibits spontaneous SHG without application of any external field [2,3]. Both phases form a complex poly-domain structure which lead us to develop a SHG-Scanning microscope to perform a more detailed study of this complex systems. First experimental 2D-SHG-Scans in this molecules show the possibility to discriminate domains of different polar and NLO-properties, allowing a better understanding and analyses of this structures. A well defined polar structuring by external fields and analyses thereof is a prerequisite for the development of non-linear-optical (NLO)-applications of banana-shaped molecules like quasi-phase-matched (QPM)-waveguiding structures [4,5] or fast NLO switches.

Incorporation in Langmuir and Langmuir–Blodgett films of symmetric fluorine substituted bent-core liquid crystals: Morphological and optical properties

“…Thus, according to the MakerFringes method, angle dependent SHG-measurements were performed for mono-and multilayer LB-structures implementing both significant P-In/P-Out and S-In/P-Out laser beam polarization geometries as explained before. The estimated NLO-coefficients are in good agreement with those reported in the literature for bent-shaped compounds composed of several benzene rings [5,18,[34][35][36][37][38][39][40].…”

Bent-Core Liquid Crystals: Their Mysterious and Attractive World

“…However, the bent-core molecules usually produced only small domains, which sometimes consist of different molecular orientations and of coexistent states of ferroelectric/antiferroelectric and homochiral/racemic states. For the structural analysis of such structures, confocal microscopy 140) and SHG microscopy 141,142) are very useful.…”

POLAR MICRO STRUCTURES OF THE B2- AND B4-PHASES OF BENT-SHAPED LC-MOLECULES RESOLVED BY NONLINEAR OPTICAL MICROSCOPY

“…Domain parameters such as alignment and ordering, size and SHG activity have to be controlled in order to develop practical photonic prototypes. 14,19,20,23 In our experiments, the sample thickness may be considered to be smaller than its characteristic coherence length (usually in the range of tenths of microns); under this limit (l Film < l Film c ) the relation between the generated SHG intensity and the intensity of the fundamental wave can be expressed as…”