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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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Generation of phase singularities with interlinked screw-edge dislocations.(a) The POM image of a grating with two slightly separated elementary dislocations of opposite signs of Burgers vector. (b) Corresponding diffraction pattern with only 0th and 1st diffraction orders shown. (c) 3D representation of the phase profile corresponding to the first-order diffraction beam. The inset shows the corresponding 2D representation of the same phase singularity. The vertical green lines mark the screw dislocations.
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f4: Generation of phase singularities with interlinked screw-edge dislocations.(a) The POM image of a grating with two slightly separated elementary dislocations of opposite signs of Burgers vector. (b) Corresponding diffraction pattern with only 0th and 1st diffraction orders shown. (c) 3D representation of the phase profile corresponding to the first-order diffraction beam. The inset shows the corresponding 2D representation of the same phase singularity. The vertical green lines mark the screw dislocations.

Mentions: Beams with more sophisticated controlled singular phase distributions can be obtained from a Gaussian beam diffracted by phase gratings with multiple edge dislocations. For example, when two spatially separated elementary edge dislocations of opposite Burgers vectors b are introduced into a periodic grating (Fig. 4a), the intensity profiles of beams in the diffraction pattern shown in Fig. 4b change dramatically as compared to diffraction patterns due to gratings with individual edge dislocations (Fig. 3). The corresponding phase distributions (Fig. 4c) reveal inter-connected screw-edge dislocations: two screw dislocations having elementary charge of opposite signs are connected by an edge dislocation in the phase profile across which the phase has a sharp jump from −π to +π262728. On the other hand, two slightly separated dislocations with the same b in a grating shown in the supplementary Fig. S6a produce two off-axis rotating elementary phase singularities of the same sign N = ±1 in the ndo = ±1 beams and 2ndo such defects in the beams of higher order26. The angle α between the straight line linking two phase singularities in the first-order beam and the straight line between two edge dislocations in the grating varies with the distance dc from the phase grating to the camera detector as shown in the supplementary Fig. S6b, according to theoretically predicted dependence (see supplementary material)26.


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)

Generation of phase singularities with interlinked screw-edge dislocations.(a) The POM image of a grating with two slightly separated elementary dislocations of opposite signs of Burgers vector. (b) Corresponding diffraction pattern with only 0th and 1st diffraction orders shown. (c) 3D representation of the phase profile corresponding to the first-order diffraction beam. The inset shows the corresponding 2D representation of the same phase singularity. The vertical green lines mark the screw dislocations.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Generation of phase singularities with interlinked screw-edge dislocations.(a) The POM image of a grating with two slightly separated elementary dislocations of opposite signs of Burgers vector. (b) Corresponding diffraction pattern with only 0th and 1st diffraction orders shown. (c) 3D representation of the phase profile corresponding to the first-order diffraction beam. The inset shows the corresponding 2D representation of the same phase singularity. The vertical green lines mark the screw dislocations.
Mentions: Beams with more sophisticated controlled singular phase distributions can be obtained from a Gaussian beam diffracted by phase gratings with multiple edge dislocations. For example, when two spatially separated elementary edge dislocations of opposite Burgers vectors b are introduced into a periodic grating (Fig. 4a), the intensity profiles of beams in the diffraction pattern shown in Fig. 4b change dramatically as compared to diffraction patterns due to gratings with individual edge dislocations (Fig. 3). The corresponding phase distributions (Fig. 4c) reveal inter-connected screw-edge dislocations: two screw dislocations having elementary charge of opposite signs are connected by an edge dislocation in the phase profile across which the phase has a sharp jump from −π to +π262728. On the other hand, two slightly separated dislocations with the same b in a grating shown in the supplementary Fig. S6a produce two off-axis rotating elementary phase singularities of the same sign N = ±1 in the ndo = ±1 beams and 2ndo such defects in the beams of higher order26. The angle α between the straight line linking two phase singularities in the first-order beam and the straight line between two edge dislocations in the grating varies with the distance dc from the phase grating to the camera detector as shown in the supplementary Fig. S6b, according to theoretically predicted dependence (see supplementary material)26.

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
Related in: MedlinePlus