Photonics of liquid-crystal structures: A review

Palto, S. P.; Blinov, L. M.; Barnik, M. I.; Лазарев, В. В.; Umanskiĭ, B. A.; Shtykov, N. M.

doi:10.1134/s106377451104016x

Cited by 36 publications

(26 citation statements)

References 27 publications

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“…In photostationary state is clearly seen a peak with a maximum around 450 nm, which corresponds to the n-π * electronic transition of the azobenzene chromophore. [23][24][25] As seen from the spectra of circularly-polarized fluorescence ( Figure S8) the left-handed component of emission has pronounced gap in intensity coincided with selective light reflection peak of the cholesteric mixture.…”

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confidence: 93%

Photochromic and fluorescent LC gels based on a bent-shaped azobenzene-containing gelator

et al. 2015

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Photochromic LC-gels based on low-molar-mass azobenzene-containing bentshaped gelator and nematic liquid crystals were prepared. LC-gels are capable of reversible melting under E-Z isomerization of azobenzene chromophores induced by UV-irradiation. It is shown that light and heat actions allow one to manipulate phase behaviour, fluidity and optical properties of the prepared LCgels. The observed phenomenon was applied for the creation of nematic and cholesteric mixtures with phototunable degree of linearly or circularly-polarized fluorescence. The elaborated systems could be considered as promising softmatter materials for optics and photonics applications. Among the different types of smart materials gels are the one of the most promising stimuli responsive systems which are gained a significant interest due to the large variety of unique properties. In particular, there are the possibilities of the fast and reversible switching of the mechanical properties under different fields and actions, such as light, pH changes, mechanical force, etc. A special interest presents lightresponsive gels [1-13] because the light is the one of the most useful and simple tools for the fast, distant and localized modification of the mechanical and optical properties of the materials including gels.Another promising type of the responsive systems are the liquid crystalline (LC) gels capable of forming of anisotropic films or layers with photo-, thermo-and electro-switchable optical properties allowing a creation of a novel type of materials with controllable supramolecular structure. [11][12][13][14][15][16][17][18][19][20][21][22] In the paper by Kato et al [13] photoinduced gel-sol transition in photochromic LC-gels with hydrogen-bonded azobenzene-containing gelators was described. Authors have demonstrated

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confidence: 93%

Photochromic and fluorescent LC gels based on a bent-shaped azobenzene-containing gelator

et al. 2015

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“…Onceĥ is perpendicular to E, the field expands the regions wheren is parallel to E, thus introducing higher spatial harmonics into the structure. Such a distorted structure creates additional reflection bands at higher frequencies (24) and dramatically reduces the laser emission intensity (21,25). Similar distortions occur not only in CLCs but also in chiral smectic C lasers when the applied field is perpendicular to theĥ axis (18).…”

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confidence: 82%

Electrically tunable laser based on oblique heliconical cholesteric liquid crystal

Xiang

Varanytsia

Minkowski

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

154

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A cholesteric liquid crystal (CLC) formed by chiral molecules represents a self-assembled one-dimensionally periodic helical structure with pitch p in the submicrometer and micrometer range. Because of the spatial periodicity of the dielectric permittivity, a CLC doped with a fluorescent dye and pumped optically is capable of mirrorless lasing. An attractive feature of a CLC laser is that the pitch p and thus the wavelength of lasing λ can be tuned, for example, by chemical composition. However, the most desired mode to tune the laser, by an electric field, has so far been elusive. Here we present the realization of an electrically tunable laser with λ spanning an extraordinarily broad range (>100 nm) of the visible spectrum. The effect is achieved by using an electric-fieldinduced oblique helicoidal (OH) state in which the molecules form an acute angle with the helicoidal axis rather than align perpendicularly to it as in a field-free CLC. The principal advantage of the electrically controlled CLC OH laser is that the electric field is applied parallel to the helical axis and thus changes the pitch but preserves the single-harmonic structure. The preserved single-harmonic structure ensures efficiency of lasing in the entire tunable range of emission. The broad tuning range of CLC OH lasers, coupled with their microscopic size and narrow line widths, may enable new applications in areas such as diagnostics, sensing, microscopy, displays, and holography.cholesteric liquid crystals | lasing | electric tunability | heliconical structure C hiral interactions in cholesteric liquid crystals (CLCs) result in supramolecular helical structures (1). The nematic directorn defining molecular orientation is perpendicular to the helix axis and rotates continuously along the axis, generating a regular rightangle helix with pitch p. Because the dielectric tensor is periodic in space, the CLC is a 1D photonic bandgap structure, selectively reflecting circularly polarized light of the same handedness as the helix. The reflection band edges are at wavelengths λ o = pn o and λ e = pn e , where n o and n e are, respectively, the ordinary and extraordinary refractive indices of the local uniaxial structure (1).In optically pumped thin layers of CLCs doped with fluorescent dyes, selective Bragg reflection of light gives rise to mirrorless lasing at the reflection band edges. Early demonstrations of lasing from CLCs (2-6) stimulated considerable interest in these easily produced micrometer-sized laser light sources due to their potential in spectroscopic, communications, sensing, and display applications. One major appeal of CLC lasers is the tunability of the emission wavelength by controlling the pitch. This can be achieved by changing the temperature (6-8), composition or cell thickness (9-11), mechanical strain in cross-linked CLC elastomers (12-14), and using reversible photochemical reactions (15, 16). The most sought-after control is via an applied electric field, which, although possible in principle (17-23), has not yet achiev...

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“…CLC formulations may be used to screen UV light and, in make‐up cosmetics, as a coloring agent to obtain opalescent and striking iridescent visual effects that depend on the incidence angle of the light and the angle of observation. Temperature and pressure sensors,29 supertwisted nematic LC displays (LCDs),30 tunable bandpass filters and rewritable color recordings,31 polarizer‐free reflective displays,32 lasing applications,33 or smart‐window prototypes take advantage of the optical properties of the cholesteric phase. Ref.…”

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confidence: 99%

Cholesteric Liquid Crystals with a Broad Light Reflection Band

2012

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The cholesteric-liquid-crystalline structure, which concerns the organization of chromatin, collagen, chitin, or cellulose, is omnipresent in living matter. In technology, it is found in temperature and pressure sensors, supertwisted nematic liquid crystal displays, optical filters, reflective devices, or cosmetics. A cholesteric liquid crystal reflects light because of its helical structure. The reflection is selective - the bandwidth is limited to a few tens of nanometers and the reflectance is equal to at most 50% for unpolarized incident light, which is a consequence of the polarization-selectivity rule. These limits must be exceeded for innovative applications like polarizer-free reflective displays, broadband polarizers, optical data storage media, polarization-independent devices, stealth technologies, or smart switchable reflective windows to control solar light and heat. Novel cholesteric-liquid-crystalline architectures with the related fabrication procedures must therefore be developed. This article reviews solutions found in living matter and laboratories to broaden the bandwidth around a central reflection wavelength, do without the polarization-selectivity rule and go beyond the reflectance limit.

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Photonics of liquid-crystal structures: A review

Cited by 36 publications

References 27 publications

Photochromic and fluorescent LC gels based on a bent-shaped azobenzene-containing gelator

Photochromic and fluorescent LC gels based on a bent-shaped azobenzene-containing gelator

Electrically tunable laser based on oblique heliconical cholesteric liquid crystal

Cholesteric Liquid Crystals with a Broad Light Reflection Band

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