Nested optical band gaps for a cholesteric elastomer slab under stress

Abstract

Using the equilibrium configuration adopted by a cholesteric elastomer elongated by the influence of a uniaxial transverse stress, the authors calculate the solution of the boundary-value problem for the reflection and transmission of obliquely incident plane waves due to a elastomer slab. The authors find a left-circularly polarized thin reflection band immersed in a wider right-circularly polarized band reflection when the elastomer is under a stress near to the critical value. Also, a deformation of the reflection band and the reduction of its bandwidth were obtained. These band gap features suggest to design a finely tuning polarization-universal optical filter.

Resonant modes for both handedness for circularly polarized light in elastomers

“…In absence of distortion they have only one reflection band for circularly polarized light of the same handedness of the helix of elastomer [1]. When the cholesteric elastomer is elongated [2] or chemically modified by affecting the cross-linking density [3], the reflection band changes and in presence of the cross-linking density appears another reflection band for the circularly polarized light of handedness opposite to helix of elastomer as is shown experimentally in the Ref. [4].…”

Band structure controlled by chiral imprinting

“…As a consequence, the elastomer slab exhibit nested band gaps similar to those found for an elastomer subjected to a mechanical stress applied perpendicularly to the elastomer-helix axis. 7 That is, a wide partial reflection band for left-circularly polarized waves contains a thinner total reflection band where the system behaves actually as a polarization-universal filter, as the one proposed by Sarkissian et al 6 In Fig. 3 we plot R RR and R LL versus and ␣ also for normal incidence.…”

“…Under specific conditions, the same structure is obtained from chiral elastomers subjected to transverse stress. 7 For both systems, the polarizationdiscriminatory feature of a standard chiral material is almost lost and both handednesses of circular polarization exhibit a very similar band gap. The fact that imprinted cholestericelastomer's configurations are also susceptible to the presence of racemic and chiral solvents 8 opens up the door not only to a mechanism for chemically controlling these optical devices but also to an optical procedure for determining quantitatively the degree of chiral segregation performed by an imprinted elastomer.…”

Structural Color Palettes of Core–Shell Photonic Ink Capsules Containing Cholesteric Liquid Crystals

“…When the helical pitch is comparable with the wavelength of visible light, CLCs display structural colors by selectively reflecting light of the same handedness in the bandgap . The structural color can be tuned by adjusting external stimuli such as temperature, electric field, light, mechanical stress, and pH making CLCs promising for various photonic applications, including reflection‐mode displays, colorimetric sensors, and antiforgery materials . In addition, the slow photon effect and the high photonic density of states at the band edges make CLCs useful as lasing resonators.…”

“…In addition, the core–shell capsules can serve as dual resonators for omnidirectional lasing, the capsules provide simultaneous lasing from both core and shell at different wavelengths, or selective lasing from either core or shell, according to the emitters, stop band positions, and handedness of helical structure . As the cores of the capsules remain fully fluid, the color or spectrum of the cores can vary in response to external stimuli, including temperature changes and many others . Therefore, the capsules can be used as dispersible and injectable sensors to measure the level of stimuli; a colorimetric thermometer is one example.…”