Orientational structures in cholesteric droplets with homeotropic surface anchoring

Krakhalev, M. N.; Rudyak, Vladimir Yu.; Prishchepa, O. O.; Gardymova, Anna P.; Emelyanenko, A. V.; Liu, Jui Hsiang; Zyryanov, V. Ya.

doi:10.1039/c9sm00384c

Cited by 25 publications

(29 citation statements)

References 58 publications

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“…The orientational structures in cholesteric droplets with the unique conical boundary conditions with the director tilt angle θ 0 = 50 • have been studied. In such droplets, various combinations of topological features were revealed that are inherent to both nematic droplets with conical anchoring [47] and cholesteric droplets with homeotropic boundary conditions [42]. The axisymmetric twisted axial-bipolar configuration characterised by two boojums and the surface circular defect at the droplet's equator is formed at N 0 ≤ 2.9.…”

Section: Discussionmentioning

confidence: 99%

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Optical Textures and Orientational Structures in Cholesteric Droplets with Conical Boundary Conditions

2020

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Cholesteric droplets dispersed in polymer with conical boundary conditions have been studied. The director configurations are identified by the polarising microscopy technique. The axisymmetric twisted axial-bipolar configuration with the surface circular defect at the droplet’s equator is formed at the relative chirality parameter N 0 ≤ 2.9 . The intermediate director configuration with the deformed circular defect is realised at 2.9 < N 0 < 3.95 , and the layer-like structure with the twisted surface defect loop is observed at N 0 ≥ 3.95 . The cholesteric layers in the layer-like structure are slightly distorted although the cholesteric helix is untwisted.

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Section: Discussionmentioning

confidence: 99%

“…The layer-like structure with the double twisted defect loop [33,35,[38][39][40] or structures with several points defects [36,37] are formed at large N 0 > 2.5. When 2.9 < N 0 < 5.8, the axisymmetric structure with the surface circular defect at the droplet's equator is formed [41,42].…”

Section: Introductionmentioning

confidence: 99%

Optical Textures and Orientational Structures in Cholesteric Droplets with Conical Boundary Conditions

2020

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“…In order to demonstrate manipulation of laser mode profile over p o changes, a series of modes were taken by increasing the intracavity chirality (Figure 3j). [ 29 ] When no chiral dopant is induced, no pitch will be formed within the droplet. The nematic LC droplet is therefore comparable to the mode in glass bead in a FP cavity.…”

Section: Figurementioning

confidence: 99%

Tunable Microlasers Modulated by Intracavity Spherical Confinement with Chiral Liquid Crystal

Zhang

Yuan

Qiao

et al. 2020

Advanced Optical Materials

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inside or outside a Fabry−Pérot (FP) cavity to control the optical properties of laser emission. [8][9][10][11][12][13] Most studies focused on either the tunability of laser modes or switching of lasing wavelengths. However, the capability to control both lasing spectra and laser modes in a microresonator remains challenging due to the lack of efficient mechanisms to overcome mode competitions. Conventional FP cavity relies on two highly reflected planar mirrors to form a resonator, in which whole-body interactions between the electromagnetic field and the gain medium can be utilized for intracavity detection and manipulation. [14][15][16][17][18] The structure of within the FP cavity can also alter the lasing output characteristics sensitively (e.g., laser mode, threshold, and lasing spectrum). Herein, we developed a tunable laser by configuring the optical confinement, chirality, and polarization at the nanoscale with liquid crystals (LCs) in FP microcavity. LCs have received emerging attention owing to its tunability, in which the orientation of the elongated LC molecules will change under an external stimulus. Additionally, anisotropic optical characteristics can be manipulated dynamically by changing the internal structures in cholesteric LC (CLC). Based on the unique features, LCs have been extensively used in biosensing, temperature detection, and whispering-gallery mode (WGM) laser resonators. [19][20][21][22][23][24] As the chiral dopant increases in CLC droplets, the number of periodic refractive index variation (periodic shells) increases to form higher structural confinement and chirality. Recent studies have further applied CLC microdroplets to obtain spherical or lateral confinement of optical modes. [25][26][27] In this work, we explored the lasing properties of a hybrid FP cavity by modulating light confinement and interactions in a FP resonator. Different configurations of micro-/nanostructured CLC−WGM droplet allowed the versatile design of optical confinement, chirality, and molecular orientation. Taking advantage of the vast complexity and tunability of CLCs, this novel concept provides a simple yet highly versatile method to manipulate laser modes and lasing wavelengths. Three representative CLC structures were prepared and analyzed in this work, with the pitch length (p o ) designed to be larger (p o >> λ), close to (p o ∼ λ), and smaller (p o < λ) than the lasing wavelength (λ). Figure 1a shows that as the pitch length becomes smaller, Manipulation of laser emission offers promising opportunities for the generation of new spatial dimensions and applications, particularly in nanophotonics, super-resolution imaging, and data transfer devices. However, the ability to control laser modes and wavelength in a microcavity remains challenging. Here, a novel approach is demonstrated to control laser modes by manipulating the 3D-optical confinement, chirality, and orientations in a Fabry−Pérot microcavity with cholesteric liquid crystal droplets. Different configurations of intracavity micro-/nanost...

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“…17 For these and related structures, the collective, 53 rotational, 54,55 and translational 43 motions, optical 56,57 and transport 46 properties, self-assembly within chains, 58 loops, 59 arrays [59][60][61] and clusters, 62 and interaction with colloidal particles 63 have been the focus of detailed experimental studies, mostly conducted in solid wedge-shaped and flat glass cells, and rarely in other geometries, namely microchannels 64,65 and droplets. 66,67 Cholesteric fingers of the first 14 (CF-1s) and second 10,18 (CF-2s) types are linear regions of twist about one cholesteric pitch wide, which contain line singularities in the pitch, but not in the director. 4 As both types do not contain line singularities in the director (only in the cholesteric pitch), we will refer to either of them as "non-singular fingers" in the following.…”

Section: Smentioning

confidence: 99%

Topological solitons, cholesteric fingers and singular defect lines in Janus liquid crystal shells

et al. 2020

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Orientational structures in cholesteric droplets with homeotropic surface anchoring

Abstract: The dependency of orientational structures in cholesteric droplets with homeotropic surface anchoring on the helicity parameter has been studied by experiment and simulations.

Cited by 25 publications

References 58 publications

Optical Textures and Orientational Structures in Cholesteric Droplets with Conical Boundary Conditions

Optical Textures and Orientational Structures in Cholesteric Droplets with Conical Boundary Conditions

Tunable Microlasers Modulated by Intracavity Spherical Confinement with Chiral Liquid Crystal

Topological solitons, cholesteric fingers and singular defect lines in Janus liquid crystal shells

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