Electrically Tunable Selective Reflection of Light from Ultraviolet to Visible and Infrared by Heliconical Cholesterics

Xiang, Jie; Li, Yannian; Li, Quan; Paterson, Daniel A.; Storey, John M. D.; Imrie, Corrie T.; Lavrentovich, Oleg D.

doi:10.1002/adma.201500340

Cited by 286 publications

(214 citation statements)

References 35 publications

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“…This phenomenon is referred to as the selective reflection [1] or, alternatively, the Bragg circular diffraction for electromagnetic and acoustic waves [2]. The results obtained are readily generalized for any material with a helix-like response, including widely tunable heliconical structures [3]. The selective reflection obstructs observation of localized states when the order at the interface or at the structural defect is disturbed.…”

Section: Introductionmentioning

confidence: 95%

Chiral Optical Tamm States: Temporal Coupled-Mode Theory

et al. 2017

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Abstract:The chiral optical Tamm state (COTS) is a special localized state at the interface of a handedness-preserving mirror and a structurally chiral medium such as a cholesteric liquid crystal or a chiral sculptured thin film. The spectral behavior of COTS, observed as reflection resonances, is described by the temporal coupled-mode theory. Mode coupling is different for two circular light polarizations because COTS has a helical structure replicating that of the cholesteric. The mode coupling for co-handed circularly polarized light exponentially attenuates with the cholesteric layer thickness since the COTS frequency falls into the stop band. Cross-handed circularly polarized light freely goes through the cholesteric layer and can excite COTS when reflected from the handedness-preserving mirror. The coupling in this case is proportional to anisotropy of the cholesteric and theoretically only anisotropy in magnetic permittivity can ultimately cancel this coupling. These two couplings being equal result in a polarization crossover (the Kopp-Genack effect) for which a linear polarization is optimal to excite COTS. The corresponding cholesteric thickness and scattering matrix for COTS are generally described by simple expressions.

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Section: Introductionmentioning

confidence: 95%

Chiral Optical Tamm States: Temporal Coupled-Mode Theory

et al. 2017

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“…1 A and B. When the electric field is applied parallel to the helicoidal axis, E kĥ, and increases, the molecules tend to align along the field, thus reducing the angle θ and, as shown both theoretically (26, 27) and experimentally (28,29), reducing the pitch, p ∝ 1=E (Fig. 1 A and B).…”

mentioning

confidence: 62%

Electrically tunable laser based on oblique heliconical cholesteric liquid crystal

Xiang

Varanytsia

Minkowski

et al. 2016

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

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152

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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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“…[101] By systematically increasing the electric field, a blue shift in the reflection band with changes in the positon of reflection notch from 1100 to 300 nm was observed. The limitation of these systems is that they reflect only a fraction of infrared energy because of their inherent narrowband nature, which results in limited impact on indoor temperature.…”

Section: Reflection Based Technologiesmentioning

confidence: 96%

Infrared Regulating Smart Window Based on Organic Materials

Khandelwal

Schenning

Debije

2017

Advanced Energy Materials

324

220

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(IR), here defined as light with wavelengths between 700 nm and 2500 nm, accounts for around 50% of the total energy emitted by the sun reaching Earth (Figure 1b), [3,4] and this light produces interior heating but is invisible to the unaided eye.The absorption of sunlight by building materials and passage of IR through transparent surfaces such as windows is responsible for much of the interior overheating of office rooms, automobile interiors, greenhouses, and other similar spaces. The use of artificial cooling and heating systems will only increase with the continued influence of global climate change, with energy used for cooling systems surpassing energy used for heating around the year 2070, and a 40 fold increase in air cooling energy use is expected by 2100. [5] By controlling the influx of radiant heat transfer, calculations show that more than 50% of the energy used in lighting, heating and cooling could be saved by deploying better control systems over only 18% of available window stock. [6] In areas with human inhabitants employing windows, more aspects must be considered than simply reducing the use of energy in the room: any switchable window used in, for example, a commercial office space has several other requirements that must be met before it may be installed. Among these requirement are reasonably fast switching speeds [7] (although for IR control, relatively longer times compared to visible light switching should be acceptable), good optical transparency with minimum haze, an acceptable device lifetime, [8] and functionality over a range of exterior temperatures. Controlling the excess of solar energy without compromising the visible transparency of the window is an important consideration for human health: maintaining inside/outside contact and daylighting are vital in retaining well-being and productivity, as well as providing economic and aesthetic gain by reducing the need for artificial lighting systems. [9,10] These are challenging goals for a window to realize.A number of materials have been developed over the past few decades to maintain indoor temperatures. Many of these focus on the opaque structural building elements like walls and roofing. [10][11][12][13] Other solutions target the transparent window, employing external mechanical shutters and blinds, [14] phase change materials (PCMs), [15] thermochromic materials, [16] aerogels, [17] trapped gas in fluid membranes, [18] and even phononic materials, [19] among other options. Indeed, controlling heat passage through the window in response to changing climate conditions is a great challenge; ideally, one would accomplish Windows are vital elements in the built environment that have a large impact on the energy consumption in indoor spaces, affecting heating and cooling and artificial lighting requirements. Moreover, they play an important role in sustaining human health and well-being. In this review, we discuss the next generation of smart windows based on organic materials which can change their properties by reflecting or trans...

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Electrically Tunable Selective Reflection of Light from Ultraviolet to Visible and Infrared by Heliconical Cholesterics

Cited by 286 publications

References 35 publications

Chiral Optical Tamm States: Temporal Coupled-Mode Theory

Chiral Optical Tamm States: Temporal Coupled-Mode Theory

Electrically tunable laser based on oblique heliconical cholesteric liquid crystal

Infrared Regulating Smart Window Based on Organic Materials

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