Electro-Optics of Cubic and Tetragonal Blue Phase Liquid Crystals Investigated by Two-Beam Interference Microscopy

The electro-optic properties of cholesteric blue phase (BP) liquid crystals is investigated by two-beam interference microscopy. The technique can facilitate the evaluation of BP materials, since only a single measurement is required to determine the two important electro-optic coefficients, i.e., t...

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Published inApplied physics express Vol. 6; no. 6; pp. 062603 - 062603-4
Main Authors Yoshida, Hiroyuki, Yabu, Shuhei, Tone, Hiroki, Kikuchi, Hirotsugu, Ozaki, Masanori
Format Journal Article
LanguageEnglish
Published The Japan Society of Applied Physics 01.06.2013
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Summary:The electro-optic properties of cholesteric blue phase (BP) liquid crystals is investigated by two-beam interference microscopy. The technique can facilitate the evaluation of BP materials, since only a single measurement is required to determine the two important electro-optic coefficients, i.e., the Kerr and electrostriction coefficients, of BPs. Moreover, field-induced symmetry transitions can be observed microscopically, making this a powerful tool to investigate the structure--property relationship in BPs. Herein, we observe field-induced transitions from cubic BPs I and II to the centered tetragonal BP X, and investigate the influence of this transition on the Kerr coefficient.
Bibliography:Experimental setup of the TBIM. LS, laser; THL, tungsten halogen lamp; BS, non-polarizing beam splitter; M, aluminum mirrors; L, achromatic doublet lens; S, sample; OL, objective lens ($5\times$); P, polarizer; BPF, band-pass filter; A, analyzer; NF, notch filter; IL, imaging lens; MMF, multimode fiber; SM, spectrometer (Ocean Optics USB-4000); C, CMOS camera (Thorlabs DCC1240C). Typical datasets obtained using the TBIM. (i) Polarized reflection microscopy images, (ii) interference fringes superimposed on polarized microscopy images, or (iii) interference fringes alone can be obtained depending on the filter used. (iv) Reflection spectrum obtained simultaneously from the ITO-coated region. Data are shown for different applied fields of (a) 0, (b) 2.6, and (c) 5.3 V/μm. Field-induced phase transition into the cholesteric fonal conic texture is clearly visible at 5.3 V/μm. Electric field dependence of the relative refractive index and Bragg reflection wavelength in (a) BP I (45.7 °C) and (b) BP II (46.2 °C). Kossel Diagrams in (c) BP I (observed with $\lambda=406$ nm) and (d) BP II ($\lambda=437$ nm), showing the four-fold symmetry of BP X at electric fields above threshold. Temperature dependences of the Kerr and electro-striction coeffeicients of the sample containing (a) 7 wt % and (b) 6 wt % chiral dopant. The error bars on each point shows the deviation that can result from the fluctuations in the phase measurement, which is $3\times 10^{-4}$.
ISSN:1882-0778
1882-0786
DOI:10.7567/APEX.6.062603