The effect of an optical field on the nematic phase of the liquid crystal OCBP

Zolot’ko, A. S.; Kitaeva, V. F.; Kroó, N.; Соболев, Н. Н.; Chillag, L.

doi:10.1007/978-94-011-3180-3_10

Cited by 22 publications

(31 citation statements)

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“…The multiple diffraction rings have been demonstrated in a film made of (or a cell containing) a wide variety of materials, i.e., dense atomic vapors such as potassium and sodium,1~5) nematic liquid crystals,6~ll) solids,12) and liquids. 13) In reported experimental demonstrations using nematic liquid crystals, 6,8,9) several tens of diffraction rings have been observed at an optical intensity of several hundred watts per square centimeter for a sample thickness of several hundred micrometers; but for all the materials except for liquid crystals, the number of observed rings is fewer than two or three. The number of rings depends generally on the on-axis nonlinear phase shift suffered during the passage through the sarnple.…”

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confidence: 96%

Laser-Induced Diffraction Rings from an Absorbing Solution

Ogusu

Kohtani

Shao

1996

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We observed multiple diffraction rings of a cw Ar+ Iaser beam from a nitrobenzene solution 0L saturable absorber BDN (bis-(4-dimethylaminodithiobenzil)-nickel) caused by the spatial selL-phase modulation at low incident optical intensities. We obtained 37 rings for a 200-/Im thick sample at an optical intensity of 38 W/mm2. The refractive-index change An and effective nonlinear refractive index n2 were determined from the number of observed rings and by the z-scan technique. We obtained large values of An-0.1 and n2=-2 9xlO cm IW This large nonlinearity is attributed to a thermal effect resulting from linear absorption.The propagation of a laser beam in third-order nonlinear media with the intensity-dependent refractive index and absorption coefficient is accompanied by a variety of interesting phenomena. Among these are the selL-focusing and -defocusing, self-phase modulation, spatial ring formation, and bearn break-up. The spatial ring formation is understood to be induced by the spatial self-phase modulation arising from the laser-induced refractive index change. The multiple diffraction rings have been demonstrated in a film made of (or a cell containing) a wide variety of materials, i.e., dense atomic vapors such as potassium and sodium,1~5) nematic liquid crystals,6~ll) solids,12) and liquids.13) In reported experimental demonstrations using nematic liquid crystals,6,8,9) several tens of diffraction rings have been observed at an optical intensity of several hundred watts per square centimeter for a sample thickness of several hundred micrometers; but for all the materials except for liquid crystals, the number of observed rings is fewer than two or three. The number of rings depends generally on the on-axis nonlinear phase shift suffered during the passage through the sarnple. The phase shift depends on an optical intensity, magnitude and saturation value of the nonlinear refractive index, sample thickness, etc. The attainable refractive index change of nematic liquid crystals is about 0.1. The large nonlinearity is due to molecular reorientations of liquid crystals induced by an optical field and resulting birefringence.In this letter, we demonstrate the multiple diffraction rings from a solution of saturable absorber at low input powers and discuss the ring formation and the origin of the nonlinearity used. In fact, we accidentally found that diffraction rings were easily obtained in a solution of saturable absorber bis-(4-dimethylarnino-dithiobenzil)-nickel (BDN) during a z-scan measurement of its nonlinearity. We are using this dye as a nonlinear material to develop a high-speed fiber-type bistable device, the prototype of which the authors proposed earlier.14) BDN dye is a saturable absorber developed for Q-switching and modelocking of an Nd: glass laser operating at infrared.15) This dye has also been used for demonstrating a bistable FabryPerot resonator with a switching time of the order of nanoseconds.16) We used nitrobenzene as a solvent in our experiment. This solvent was selected for its durabi...

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confidence: 96%

Laser-Induced Diffraction Rings from an Absorbing Solution

Ogusu

Kohtani

Shao

1996

OPT REV

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“…The anisotropy of the elastic coefficients might also play a role. It is indeed known to lead to anisotropic reorientation patterns in conventional self-phase-modulation experiments [22]. More recently, broken circular symmetry has also been reported in the context of NLC reorientation under spin-orbit interaction [23].…”

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confidence: 91%

Observation of Self-Induced Optical Vortex Precession

Ketara

Brasselet

2013

Phys. Rev. Lett.

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“…16 This NLO effect on molecular reorientation has attracted attention owing to high NLO efficiency. [17][18][19][20][21][22] When the initial homeotropic (out-of-plane) orientation is changed to homogeneous orientation with light, a large change in the refractive index is induced, which leads to a large NLO effect. In addition, nematic LCs that have high optical nonlinearity reorient the molecular director at lower light intensity compared with conventional materials.…”

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Effect of surface treatment on molecular reorientation of polymer-stabilized liquid crystals doped with oligothiophene

Usui

Katayama

Wang

et al. 2016

Polym J

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Irradiation of dye-doped liquid crystals (LCs) with linearly polarized light leads to molecular reorientation, which manifests functional properties for various nonlinear optical (NLO) applications. Material designs with lower light intensity thresholds for molecular reorientation have been explored, and nematic LCs have been one of the most attractive choices because of the high NLO properties. Here we present a different approach to reduce light intensity for reorientation by modifying a substrate surface that controls initial molecular orientation in polymer-stabilized nematic LCs doped with oligothiophene. The surface of the glass substrate was treated with various concentrations of a silane coupler. Water contact angle measurement and analysis of samples using polarized optical microscopy revealed that surface anchoring in the initial state decreased as the silane coupler concentration decreased. The threshold intensity was successfully reduced by 30% simply by optimizing the silane coupler concentration. This finding clearly indicates that weak surface anchoring is key to the reduction of light intensity for molecular reorientation. INTRODUCTIONLiquid crystal (LC) materials have had a great impact on our modern information society. 1-3 Various LC materials and devices including LC displays, 3 smart windows, 4 reconfigurable optical elements 5 and tunable optical metamaterials 6 have been realized. 2 In these applications, light modulation is the most important factor and is achieved by orientational changes of LC molecules using an external field.Molecular reorientation of conventional LCs has been performed by an electric field. However, molecular reorientation triggered by an optical field has attracted attention because it enables the development of all-optical devices. 7,8 Such photoinduced molecular reorientation includes photochemical and photophysical processes. Photochemical processes control LC orientation through a photochemical reaction, for example, photoisomerization, photocrosslinking or photodegradation. [8][9][10][11][12][13][14] In contrast, a photophysical process exploits the nonlinear optical (NLO) effects of an LC. 7,15 When a homeotropic LC is vertically irradiated with linearly polarized light, the interaction between the optical field and the LC molecules generates a torque to rotate the molecular director along the polarization direction, leading to homogeneous (in-plane) orientation. On the other hand, rotation of the molecular director is disturbed both by the interaction between LCs and the glass substrate surface, a process which is also called surface anchoring, and by bulk elasticity. These torques reach a balance that determines a specific light intensity that allows

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The effect of an optical field on the nematic phase of the liquid crystal OCBP

Cited by 22 publications

References 3 publications

Laser-Induced Diffraction Rings from an Absorbing Solution

Laser-Induced Diffraction Rings from an Absorbing Solution

Observation of Self-Induced Optical Vortex Precession

Effect of surface treatment on molecular reorientation of polymer-stabilized liquid crystals doped with oligothiophene

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