Deformed lying helix transition and lasing effect in cholesteric LC layers at spatially periodic boundary conditions

Palto, S. P.; Shtykov, N. M.; Kasyanova, I. V.; Гейвандов, А. Р.; Rybakov, D. O.; Simdyankin, I. V.; Артемов, В. В.; Gorkunov, M. V.

doi:10.1080/02678292.2019.1655169

Cited by 10 publications

(11 citation statements)

References 26 publications

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“…Thus, all the parameters (elastic coefficients, low frequency dielectric anisotropy and optical anisotropy) used in the current simulations are close to values characteristic of the E7 LC. The boundary conditions are also close to those achieved experimentally in [16]. Despite some preliminary experimental study of the lasing in the DLH systems done in [16], the results of this numerical study are still to be tested experimentally.…”

Section: Numerical Simulation Methodssupporting

confidence: 72%

“…The boundary conditions are also close to those achieved experimentally in [16]. Despite some preliminary experimental study of the lasing in the DLH systems done in [16], the results of this numerical study are still to be tested experimentally.…”

Section: Numerical Simulation Methodssupporting

confidence: 72%

“…The simulations include two stages. At the first stage a DLH transition [16] is simulated, when the virtual CLC layer with the planar texture (helix axis along the layer normal) is transformed by an electric field to the DLH state. At the second stage the optical and lasing properties of the DLH state are studied for different extents of the helix deformation.…”

Section: Numerical Simulation Methodsmentioning

confidence: 99%

“…The parameters of the virtual CLC in this study correspond to a real CLC material that was designed and experimentally studied in the work [16]. This experimental CLC was made on the basis of the popular E7 (Merck) nematic mixture by doping it with both optically active compound, providing a natural helix pitch of 260 nm, and DCM lasing dye.…”

Section: Numerical Simulation Methodsmentioning

confidence: 99%

“…Typically, additional electric fields and temperature treatment are necessary in order to get the ULH textures. Recently, it was demonstrated that CLC layers with the helix axis along the normal plane can be transformed to the layers with the in-plane helix axis under a permanently applied electric field in cells with the periodic (planar/homeotropic) boundary conditions [16]. However, because the electric field is permanently applied, the lying helix is deformed (it is why such CLC layers were called in [16], deformed lying helix (DLH) layers).…”

Section: Introductionmentioning

confidence: 99%

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The Field-Induced Stop-Bands and Lasing Modes in CLC Layers with Deformed Lying Helix

Palto

2019

Crystals

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Waveguide optical properties of a cholesteric liquid crystal (CLC) layer with a deformed lying helix (DLH) have been studied by numerical simulations using the finite difference time domain method. The DLH structure, when the helix’s axis is oriented in plane of a CLC layer, is induced by an electric field in a virtual CLC cell with periodic (planar/homeotropic) boundary conditions at one of the alignment surfaces. This in-plane helical structure is stable only in a permanently applied electric field providing the helix deformation. In this work the polarized light reflectance spectra have been studied at different electric fields and light impingement into a waveguide formed by the DLH layer. It is found that for light propagating along the helix axis the reflectance spectrum has multiple stop-bands centred at wavelengths , which is different from set of bands located at , and characteristic of CLC spectra for the Grandjean-plane textures subjected to distortion by an electric or magnetic field perpendicular to the helix axis, where j is a natural number, p is the helix pitch and is the average refractive index. Each of the higher order (j > 1) bands consists of three polarization-dependent sub-bands. In the case of an amplifying CLC DLH layer, depending on an extent of the helix deformation, the lasing modes can be excited at different edges of the sub-bands. While at the strongest deformation the lasing is preferable at the edges of the central sub-band; a lower extent of deformation makes favourable conditions for the lasing at edges of the two other sub-bands.

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Section: Numerical Simulation Methodssupporting

confidence: 72%

Section: Numerical Simulation Methodssupporting

confidence: 72%

Section: Numerical Simulation Methodsmentioning

confidence: 99%

Section: Numerical Simulation Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Field-Induced Stop-Bands and Lasing Modes in CLC Layers with Deformed Lying Helix

Palto

2019

Crystals

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Photoaligned Chiral Liquid Crystal Grating with Hysteresis Switching

Nys

Berteloot

Neyts

2022

Advanced Optical Materials

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ubiquitous in nature (beetle exoskeletons, DNA, etc.) and show many intriguing material properties. CLC is a versatile soft matter system to study chiral superstructures and can be successfully applied in electro-optic devices including color filters, reflective displays, tunable lasers, beam steering devices, etc. [3a,6] The self-assembly of CLC in a periodic helical structure leads to the formation of a photonic bandgap for circularly polarized light and is often exploited in these devices.The presence of chirality in the LC material often gives rise to the existence of multiple metastable states, depending on the anchoring properties, the amount of chirality, and the cell pretreatment. [7,8] Even in cells with uniform planar anchoring, regions with a different number of chiral periods can coexist. In general, different cooling rates, electricfield treatments or optical excitations can give rise to another chiral bulk configuration. Textural transitions in the CLC state often give rise to hysteresis behavior in the electro-optic switching. In some cases this is unwanted and textural transitions are suppressed (e.g., by polymer stabilization) to obtain fast and hysteresis free optical switching. [7a] However, the formation of different metastable topological structures, relying on the competition between surface anchoring, elasticity, and chirality, is sometimes also actively sought for. It is well-known that confinement-unwound CLC systems offer an interesting playground for the formation of cholesteric fingers, bubbles and elastic quasiparticles. [8] Dynamic tuning and reconfiguring of these (metastable) topological states, by low-frequency or optical-frequency electric fields, has been demonstrated and light control by this soft-photonics platform was investigated. [9] The use of uniform alignment layers, as obtained by mechanical rubbing at the confining substrates, has been well studied but limits the number of director configurations that can be achieved. During the last decades a lot of attention was given to photoalignment techniques that allow spatially nonuniform alignment with high resolution and offer the flexibility to stabilize complex LC configurations. At the inner surface of the two confining substrates a photosensitive material can be deposited that adopts a preferential orientation, determined by the polarization direction of incident blue or UV light. Patterning of the alignment direction has been demonstrated with the help of interference illumination, direct-write illumination, plasmonic patterning, illumination structured by a spatial light modulator (SLM), etc. [10] Different alignment patterns at the top and bottom substrate can be combined, by assembling the cell after Metastable topological states are known to arise when chiral liquid crystal (CLC) is infiltrated in a geometry with strong confinement. This study demonstrates an alternative approach to obtain multistable states, by combining patterned surface anchoring with CLC in a less confined geometry. Long pitch CLC is introduc...

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Flexoelectric effects on escaped twisted configurations of nematic liquid crystal 5CB with chiral dopants in a cylindrical cavity

et al. 2020

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Deformed lying helix transition and lasing effect in cholesteric LC layers at spatially periodic boundary conditions

Cited by 10 publications

References 26 publications

The Field-Induced Stop-Bands and Lasing Modes in CLC Layers with Deformed Lying Helix

The Field-Induced Stop-Bands and Lasing Modes in CLC Layers with Deformed Lying Helix

Photoaligned Chiral Liquid Crystal Grating with Hysteresis Switching

Flexoelectric effects on escaped twisted configurations of nematic liquid crystal 5CB with chiral dopants in a cylindrical cavity

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