Light-controlled helical pitch and dynamic gratings

Boychuk, V. N.; Gerus, Igor I.; Iljin, Andrey G.; Parka, Janusz

doi:10.2478/s11772-009-0009-8

Cited by 9 publications

(8 citation statements)

References 16 publications

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“…Final LC mixtures were introduced into cells having different gap -from 1-2 to 20 µm. The exact procedures of cell preparation and details of the properties of LC systems were reported elsewhere [4,10,12].…”

Section: Experimental Techniquesmentioning

confidence: 99%

“…The beam of He-Ne laser (632.8 nm) was used for probing the residual grating kinetics. A simple photo-diode measuring system was described elsewhere [10,12].…”

Section: Experimental Techniquesmentioning

confidence: 99%

“…Chiral nematic LC's have been successfully employed for light modulation due to electrically-controlled optical activity [1,2], switchable diffractive gratings [3] or as the media for dynamic holography with high diffraction efficiency [4,5]. A very low energy is needed for the substantial change of the intrinsic helical pitch when photosensitive chiral additives are used that allowed for efficient colour image recording [6,7], tunable CLC lasers [8,9], light polarisation control [10,11] as well as diffraction grating recording [12].…”

Section: Introductionmentioning

confidence: 99%

“…In the very simple consideration, however, it is possible to limit the account of light-induced changes in CLC with the only two parameters: optical activity of LC layer (resulting in the modulation of the light polarisation plane orientation, ψ Δ , of the outcoming wave) and the average refractive index of the medium (accounted for the modulation of the usual phase retardation, λ π δ nd Δ = 2 ) [12]. The intensity of light wave diffracting on such a grating was shown to be: modulation of either the pitch or refractivity will result in a strong detuning of the probing light wave with respect to SR maximum and will bring in a strong nonlinear response of CLC over a very wide temporal range.…”

Section: Introductionmentioning

confidence: 99%

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Dynamic gratings in a chiral nematic liquid crystal

Iljin¹,

Salo

Tereshchenko³

2010

SPIE Proceedings

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Extremely strong dispersion of light is characteristic of the frequency domain of photonic band gap (PBG) boundary that in case of a chiral nematic liquid crystal (CLC) results in a strong frequency dependence of the optical activity of a CLC layer.In the present work the nonlinear behaviour of the rotation of light polarisation plane is investigated in the spectral region of the selective reflection (SR) band when the light-induced modulation of the helical pitch is achieved by means of the either temperature pitch dependence or photo-stimulated changes of the molecular conformation of the chiral dopant. Nonlinear optical modulation of the optical activity allows for recording of dynamic diffraction gratings with peculiar polarisation states of the diffracting orders. At the edge of the SR band the change of phase retardation between circular eigen waves of differing handedness well exceeds pi/2 even for a few-micron-thick LC layer. Given the proper choice of the experimental parameters the effective parameter of cubic nonlinearity in such a system could surmount by orders of magnitude that characteristic of the "giant" optical nonlinearity of liquid crystals. Chiral nematic LC with light-controlled helical pitch were investigated from the standpoint of diffraction grating recording. The experimental data have shown a strong potential of these media in different aspects of optical signal processing, all-optical switching and photonics. Theoretical modelling has provided an excellent agreement with the experiment, the role of elastic constrains on the grating formation has been also taken into consideration.

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Section: Experimental Techniquesmentioning

confidence: 99%

“…The beam of He-Ne laser (632.8 nm) was used for probing the residual grating kinetics. A simple photo-diode measuring system was described elsewhere [10,12].…”

Section: Experimental Techniquesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Dynamic gratings in a chiral nematic liquid crystal

Iljin¹,

Salo

Tereshchenko³

2010

SPIE Proceedings

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“…Optimizing liquid crystal mixtures is required to know their physical properties which have an influence on switching times, contrast ratio and power consumption [1][2][3][4][5]. One of the most difficult and problematic to measure is a twist elas− tic constant K 22 .…”

Section: Introductionmentioning

confidence: 99%

Investigations of twist elastic constant K22 of new nematic liquid crystal materials using threshold IPS method

Parka

Dąbrowski

Kowerdziej

2011

Opto-Electronics Review

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The liquid crystal technology is one of the most popular at the present time. To the most important parameters of liquid crystals belong optical anisotropy, viscosity, and twist elastic constants. One of the most difficult and problematic to measure parameters is a twist elastic constant K22. For new liquid crystalline materials, we have to characterize their physical properties, also a twist elastic constant K22.As a final result of this work, a twist elastic constant of new nematic liquid crystal materials was investigated. In this paper, a transmission-voltage characteristic of the in-plane switching cell was observed to find Freedericksz threshold, and then twist elastic constants could have been calculated. The method was checked on well-characterized materials E7 and 6-CHBT and its accuracy was better than 20%. In addition, the temperature dependence of K22 was determined for all materials.

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Transient optically induced grating and underlying transport process in bent-core nematics

Hao

Jing

Xiang

et al. 2022

Journal of Applied Physics

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In this paper, we have applied a holographic time-of-flight technique with a nanosecond laser pulse to perform time-resolved measurements of optically induced gratings in bent-core nematics formed by a new kind of liquid crystal (LC). The effects of the electric field, laser pulse energy, temperature, and light intensity pattern on the photocharge transport process were investigated systematically. The results indicate that some peculiar features, such as high photosensitivity, relatively large mobility, and negative conductivity anisotropy, were present in the studied soft-matter system. Furthermore, a coupling between the optically induced grating and electrically induced convection was observed, which revealed a competitive state between them via the transport process. Thus, a better understanding of the carrier transport process involving photosensitivity and response time will help to tailor LC devices toward novel optical applications.

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Light-controlled helical pitch and dynamic gratings

Cited by 9 publications

References 16 publications

Dynamic gratings in a chiral nematic liquid crystal

Dynamic gratings in a chiral nematic liquid crystal

Investigations of twist elastic constant K22 of new nematic liquid crystal materials using threshold IPS method

Transient optically induced grating and underlying transport process in bent-core nematics

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