Self-induced liquid crystal q-plate by photoelectric interface activation

Kravets, Nina; Podoliak, Nina; Kaczmarek, Malgosia; Brasselet, Étienne

doi:10.1063/1.5082598

Cited by 12 publications

(9 citation statements)

References 29 publications

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“…Treating the cell confining walls (both ITO-coated glass and the interface of Fe/LN with the LC) can provide a homeotropic anchoring condition for the LC, corresponding with an unperturbed condition. In the recent experimental work of Kravets and co-workers, 39 it was shown that the photoassisted dc electric field can induce spin–orbit optical vortex generation with high purity and efficiency (>90%). Here, light induced photovoltaic (PV) field in the Fe/LN has a distribution in the LC media.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Prediction of Umbilics Creation in Nematic Liquid Crystals with Positive Dielectric Anisotropy

Habibpourmoghadam

2019

ACS Omega

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Optically assisted electrical generation of umbilic defects, arising in homeotropically aligned nematic liquid crystal cells and known as topological templates for the generation of optical vortices, are reported in nematic liquid crystals with positive dielectric anisotropy in detail. It is shown that nematic liquid crystals with positive dielectric anisotropy can serve as a stable and efficient medium for the optical vortex generation from both linearly and circularly polarized input Gaussian beams. Hybrid cells made from a thin layer of nematic liquid crystal confined between a photoresponsive slab of iron-doped lithium niobate and a glass plate coated with an active material, i.e., indium tin oxide, were studied. Exposure to a laser beam locally induces a photovoltaic field in the iron-doped lithium niobate substrate, which can penetrate into the liquid crystal film and induce realignment of molecules. The photovoltaic field drives charge carrier accumulation at the interface of indium tin oxide with the liquid crystal, which effectively modifies the shape and symmetry of the electric field. The photovoltaic field has a continuous radial distribution in the transverse xy-plane, weakening with increasing distance from the light irradiation center, where the electric field is normal to the cell plane. Umbilics are created as a result of the liquid crystal tendency to realign parallel to the electric field. Numerical studies of the transmitted intensity profiles in between linear polarizers reveal optical vortex pattern (of four and eight brushes) characteristics for the umbilical defects. The application of crossed circular polarizers results in annular-shaped intensity patterns as a result of spin-to-orbital angular momentum conversions, which give rise to the optical vortices.

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Section: Introductionmentioning

confidence: 99%

Theoretical Prediction of Umbilics Creation in Nematic Liquid Crystals with Positive Dielectric Anisotropy

Habibpourmoghadam

2019

ACS Omega

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“…Electric field in the illuminated NLC cell by a light beam at normal incident to the surfaces can have a fringe profile in the planar configuration as a result of the SPR effect. The induced fringe electric field inside the LC volume is capable of realigning NLCs (with positive and negative dielectric anisotropies) from initial homeotropic alignment when shone by a low laser power (of a few mW) at a reduced threshold voltage [74][75][76][77], as schematically shown in Figure 4. Independent of the sign of the dielectric anisotropy, radial director field distributions in the transverse plane were seen as a result of director realignments from initial homeotropic alignment induced by the SPR effect [74][75][76][77].…”

Section: Generation Of Optical Vortices In the Nlc Context Due To The Spr Effectmentioning

confidence: 99%

“…The induced fringe electric field inside the LC volume is capable of realigning NLCs (with positive and negative dielectric anisotropies) from initial homeotropic alignment when shone by a low laser power (of a few mW) at a reduced threshold voltage [74][75][76][77], as schematically shown in Figure 4. Independent of the sign of the dielectric anisotropy, radial director field distributions in the transverse plane were seen as a result of director realignments from initial homeotropic alignment induced by the SPR effect [74][75][76][77]. This leads to the formation of optical vortices (Ovs) [78][79][80] from an incident plane wave.…”

Section: Generation Of Optical Vortices In the Nlc Context Due To The Spr Effectmentioning

confidence: 99%

Photorefractive Effect in NLC Cells Caused by Anomalous Electrical Properties of ITO Electrodes

Habibpourmoghadam

2020

Crystals

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In a pure nematic liquid crystal (NLC) cell, optically induced charge carriers followed by transports in double border interfaces of orientant/LC and indium-tin-oxide (ITO)/orientant (or LC) can cause removal of screening of the static electric field inside the LC film. This is called surface photorefractive effect (SPR), which induces director field reorientation at a low DC electric field beyond the threshold at a reduced Fréedericksz transition and, as a result, a modulation of the LC effective refractive index. The studies conducted on the photoinduced opto-electrical responses in pure nematic LC cells biased with uniform static DC electric fields support the SPR effect (attributed to the photoelectric activation of the double interfaces). The SPR effect was further studied in LC cells with photoresponsive substrates, which act as a source of a bell-shaped electric field distribution in the LC film if no ITO electrode was employed. In an equipped cell with ITO, the photovoltaic electric field induces charge carrier redistribution in the ITO film, hence the SPR effect. This paper is aimed at highlighting all the evidences supporting ITO film as one of the fundamental sources of the SPR effect in pure NLC cells under the condition of applying low optical power and low DC voltage. An optically induced fringe electric field stemming from inhomogeneous photo-charge profiles near the electrode surfaces is expected in the LC film due to the semiconducting behavior of the ITO layer.

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“…Indeed, several pinning strategies have been proposed to fix them in place, hence getting rid of previous limitations associated to random location of the defects [13] while preserving electrical tuning capabilities. Namely, boundary-assisted electrical pinning using pixelated electrodes [15], optically-assisted electrical pinning using photoresponsive substrates under ac [16] or dc [17] electric fields, and magnetic pinning using static ring magnets [18]. All these works offer a palette of clear aperture ranging typically over three decades from microscopic to macroscopic scales, as illustrated in figure 1.…”

Section: Introductionmentioning

confidence: 99%

Taming the swirl of self-structured liquid crystal q-plates

Kravets

Brasselet

2020

J. Opt.

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Spontaneously formed liquid crystal topological defects under external fields offer a natureassisted route to the creation of geometric phase optical vortex generators (q-plates). Here we report on the consequences of the unavoidable swirled transverse spatial distribution of the optical axis of such optical elements on the beam shaping and we propose a swirl-compensation scheme based on the arithmetic of geometric phase optical elements.

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Self-induced liquid crystal q-plate by photoelectric interface activation

Cited by 12 publications

References 29 publications

Theoretical Prediction of Umbilics Creation in Nematic Liquid Crystals with Positive Dielectric Anisotropy

Theoretical Prediction of Umbilics Creation in Nematic Liquid Crystals with Positive Dielectric Anisotropy

Photorefractive Effect in NLC Cells Caused by Anomalous Electrical Properties of ITO Electrodes

Taming the swirl of self-structured liquid crystal q-plates

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