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Laser-directed hierarchical assembly of liquid crystal defects and control of optical phase singularities.

Ackerman PJ, Qi Z, Lin Y, Twombly CW, Laviada MJ, Lansac Y, Smalyukh II - Sci Rep (2012)

Bottom Line: However, they are typically hard to control in a reliable manner.Here we describe facile erasable "optical drawing" of self-assembled defect clusters in liquid crystals.Our findings bridge the studies of defects in condensed matter physics and optics and may enable applications in data storage, singular optics, displays, electro-optic devices, diffraction gratings, as well as in both optically- and electrically-addressed pixel-free spatial light modulators.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA.

ABSTRACT
Topological defect lines are ubiquitous and important in a wide variety of fascinating phenomena and theories in many fields ranging from materials science to early-universe cosmology, and to engineering of laser beams. However, they are typically hard to control in a reliable manner. Here we describe facile erasable "optical drawing" of self-assembled defect clusters in liquid crystals. These quadrupolar defect clusters, stabilized by the medium's chirality and the tendency to form twisted configurations, are shaped into arbitrary two-dimensional patterns, including reconfigurable phase gratings capable of generating and controlling optical phase singularities in laser beams. Our findings bridge the studies of defects in condensed matter physics and optics and may enable applications in data storage, singular optics, displays, electro-optic devices, diffraction gratings, as well as in both optically- and electrically-addressed pixel-free spatial light modulators.

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Laser-generated structures formed by twist-escaped disclination clusters.(a) POM image of a spiral structure. (b) POM image of an optically-generated phase grating composed of the finger structures. The inset shows the corresponding diffraction pattern obtained using a HeNe laser beam. (c) “Topological cat” from the cover of Ref.9 generated by steering the focused laser beam in the LC cell. (d) (e) Schematics of the director structure with a quadrupole of disclinations of positive and negative half-integer strengths (red and green filled circles, respectively) in (d) a nematic and (e) a cholesteric LC with the qudrupole of the defects running along the finger's length. (f) Experimental and (g) computer-simulated vertical 3PEF-PM cross-sections of the finger's structure in a plane orthogonal to the finger. (h) Computer-simulated director structure in the vertical cross-section of an individual finger. The director fields are visualized by use of cylinders representing rod-like molecules of the LC. “P” and “A” in (a) (b) and (c) mark crossed polarizer and analyzer in POM.
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f1: Laser-generated structures formed by twist-escaped disclination clusters.(a) POM image of a spiral structure. (b) POM image of an optically-generated phase grating composed of the finger structures. The inset shows the corresponding diffraction pattern obtained using a HeNe laser beam. (c) “Topological cat” from the cover of Ref.9 generated by steering the focused laser beam in the LC cell. (d) (e) Schematics of the director structure with a quadrupole of disclinations of positive and negative half-integer strengths (red and green filled circles, respectively) in (d) a nematic and (e) a cholesteric LC with the qudrupole of the defects running along the finger's length. (f) Experimental and (g) computer-simulated vertical 3PEF-PM cross-sections of the finger's structure in a plane orthogonal to the finger. (h) Computer-simulated director structure in the vertical cross-section of an individual finger. The director fields are visualized by use of cylinders representing rod-like molecules of the LC. “P” and “A” in (a) (b) and (c) mark crossed polarizer and analyzer in POM.

Mentions: In this work, we design a soft matter system with a delicate interplay of the effects of confinement and chirality to obtain twist-stabilized quadrupolar clusters of half-integer disclinations having opposite signs s = ±1/2 (Fig. 1). These line defects are then shaped into highly controlled computer-generated patterns, including reconfigurable phase gratings capable of inducing and controlling optical phase singularities in laser beams.


Laser-directed hierarchical assembly of liquid crystal defects and control of optical phase singularities.

Ackerman PJ, Qi Z, Lin Y, Twombly CW, Laviada MJ, Lansac Y, Smalyukh II - Sci Rep (2012)

Laser-generated structures formed by twist-escaped disclination clusters.(a) POM image of a spiral structure. (b) POM image of an optically-generated phase grating composed of the finger structures. The inset shows the corresponding diffraction pattern obtained using a HeNe laser beam. (c) “Topological cat” from the cover of Ref.9 generated by steering the focused laser beam in the LC cell. (d) (e) Schematics of the director structure with a quadrupole of disclinations of positive and negative half-integer strengths (red and green filled circles, respectively) in (d) a nematic and (e) a cholesteric LC with the qudrupole of the defects running along the finger's length. (f) Experimental and (g) computer-simulated vertical 3PEF-PM cross-sections of the finger's structure in a plane orthogonal to the finger. (h) Computer-simulated director structure in the vertical cross-section of an individual finger. The director fields are visualized by use of cylinders representing rod-like molecules of the LC. “P” and “A” in (a) (b) and (c) mark crossed polarizer and analyzer in POM.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3369196&req=5

f1: Laser-generated structures formed by twist-escaped disclination clusters.(a) POM image of a spiral structure. (b) POM image of an optically-generated phase grating composed of the finger structures. The inset shows the corresponding diffraction pattern obtained using a HeNe laser beam. (c) “Topological cat” from the cover of Ref.9 generated by steering the focused laser beam in the LC cell. (d) (e) Schematics of the director structure with a quadrupole of disclinations of positive and negative half-integer strengths (red and green filled circles, respectively) in (d) a nematic and (e) a cholesteric LC with the qudrupole of the defects running along the finger's length. (f) Experimental and (g) computer-simulated vertical 3PEF-PM cross-sections of the finger's structure in a plane orthogonal to the finger. (h) Computer-simulated director structure in the vertical cross-section of an individual finger. The director fields are visualized by use of cylinders representing rod-like molecules of the LC. “P” and “A” in (a) (b) and (c) mark crossed polarizer and analyzer in POM.
Mentions: In this work, we design a soft matter system with a delicate interplay of the effects of confinement and chirality to obtain twist-stabilized quadrupolar clusters of half-integer disclinations having opposite signs s = ±1/2 (Fig. 1). These line defects are then shaped into highly controlled computer-generated patterns, including reconfigurable phase gratings capable of inducing and controlling optical phase singularities in laser beams.

Bottom Line: However, they are typically hard to control in a reliable manner.Here we describe facile erasable "optical drawing" of self-assembled defect clusters in liquid crystals.Our findings bridge the studies of defects in condensed matter physics and optics and may enable applications in data storage, singular optics, displays, electro-optic devices, diffraction gratings, as well as in both optically- and electrically-addressed pixel-free spatial light modulators.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA.

ABSTRACT
Topological defect lines are ubiquitous and important in a wide variety of fascinating phenomena and theories in many fields ranging from materials science to early-universe cosmology, and to engineering of laser beams. However, they are typically hard to control in a reliable manner. Here we describe facile erasable "optical drawing" of self-assembled defect clusters in liquid crystals. These quadrupolar defect clusters, stabilized by the medium's chirality and the tendency to form twisted configurations, are shaped into arbitrary two-dimensional patterns, including reconfigurable phase gratings capable of generating and controlling optical phase singularities in laser beams. Our findings bridge the studies of defects in condensed matter physics and optics and may enable applications in data storage, singular optics, displays, electro-optic devices, diffraction gratings, as well as in both optically- and electrically-addressed pixel-free spatial light modulators.

Show MeSH