Tunable lasing in cholesteric liquid crystal elastomers with accurate measurements of strain

Varanytsia, Andrii; Nagai, Hiroki; Urayama, Kenji; Palffy‐Muhoray, Peter

doi:10.1038/srep17739

Cited by 75 publications

(49 citation statements)

References 29 publications

(43 reference statements)

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“…Because of the coupling between the cholesteric helix and the elastomeric network, a mechanical deformation changes the reflection color and often also the polarization . A striking demonstration was the continuous and reversible tuning toward shorter wavelengths of a CLCE film with vertical helix by stretching biaxially in the film plane, equivalent to a uniaxial compression along the helix . This mechanochromic response was then used for tunable lasing controlled by stretching the film .…”

Section: Introductionmentioning

confidence: 99%

“…A striking demonstration was the continuous and reversible tuning toward shorter wavelengths of a CLCE film with vertical helix by stretching biaxially in the film plane, equivalent to a uniaxial compression along the helix . This mechanochromic response was then used for tunable lasing controlled by stretching the film . This was also achieved using viscous liquid‐state cholesterics, but the non‐elastomeric nature of the helically modulated medium then required sandwiching between rubbery substrates …”

Section: Introductionmentioning

confidence: 99%

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Facile Anisotropic Deswelling Method for Realizing Large‐Area Cholesteric Liquid Crystal Elastomers with Uniform Structural Color and Broad‐Range Mechanochromic Response

Kizhakidathazhath

Geng

Jampani

et al. 2019

Adv Funct Materials

117

125

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Cholesteric liquid crystal elastomers (CLCEs) are soft and dynamic photonic elements that couple the circularly polarized structural color from the cholesteric helix to the viscoelasticity of rubbers: the reflection color is mechanically tunable (mechanochromic response) over a broad range. This requires uniform helix orientation, previously realized by long‐term centrifugation to ensure anisotropic deswelling, or using sacrificial substrates or external fields. The present paper presents a simple, reproducible, and scalable method to fabricate highly elastic, large‐area, millimeters thick CLCE sheets with intense uniform reflection color that is repeatably, rapidly, and continuously tunable across the full visible spectrum by stretching or compressing. A precursor solution is poured onto a substrate and allowed to polymerize into a 3D network during solvent evaporation. Pinning to the substrate prevents in‐plane shrinkage, thereby realizing anisotropic deswelling in an unprecedentedly simple manner. Quantitative stress–strain–reflection wavelength characterization reveals behavior in line with theoretical predictions: two linear regimes are identified for strains below and above the helix unwinding threshold, respectively. Up to a doubling of the sample length, the continuous color variation across the full visible spectrum repeatedly follows a volume conserving function of the strain, allowing the CLCE to be used as optical high‐resolution strain sensor.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Facile Anisotropic Deswelling Method for Realizing Large‐Area Cholesteric Liquid Crystal Elastomers with Uniform Structural Color and Broad‐Range Mechanochromic Response

Kizhakidathazhath

Geng

Jampani

et al. 2019

Adv Funct Materials

117

125

View full text Add to dashboard Cite

show abstract

“…Both stimulus‐responsive free standing films as well as LCEs confined to a solid substrate have been reported with programmable shapes and topographies . For CLC elastomers, dimensional changes along the helical pitch direction even resulted in changes in reflective color . However, simultaneously changing both the topography and reflectivity by one stimulus remains a challenge.…”

Section: Introductionmentioning

confidence: 99%

Easily Processable and Programmable Responsive Semi‐Interpenetrating Liquid Crystalline Polymer Network Coatings with Changing Reflectivities and Surface Topographies

Kragt

Broer

Schenning

2017

Adv Funct Materials

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The fabrication of stimulus-responsive coatings that change both reflectivity and topography is hampered by the lack of easy processable, patternable, and programmable elastomers. Here, an easily applied reflective coating based on a semi-interpenetrating polymer network composed of a liquid crystal elastomer and a liquid crystal network (>15 wt%) is reported. The reflective wavelength of these polysiloxane elastomer photonic coatings can be readily programed by the concentration of chiral reactive mesogen dopant that forms the network. The coatings show a fast and reversible decrease in reflection band intensity with increasing temperature, which can be tuned by the polymer network density. In addition, hierarchical surface relief structures are prepared, which can be reversibly changed with temperature.

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“…4,5 In the presence of a gain medium, laser action can occur at the photonic bandedge(s) through optical excitation-usually termed the bandedge lasing. To date, a great deal of effort has been devoted to achieve a wide dynamic tuning range of the lasing wavelength with the aid of external inputs, such as electric field 6,7 , heat 8,9 , light 10 , and mechanical stress 11 . However, the post-2 fabrication selection between the LWE and SWE lasing modes is seldom discussed 12,13 .…”

mentioning

confidence: 99%

Electrically assisted bandedge mode selection of photonic crystal lasing in chiral nematic liquid crystals

Wang

Chen

Yang

et al. 2018

Applied Physics Letters

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Selection of the bandedge lasing mode of a photonic crystal laser has been realized in a fluorescent dye doped chiral nematic liquid crystal by exerting electrical control over the mode competition. The bandedge lasing can be reversibly switched from the short-wavelength edge mode to the long-wavelength edge mode by applying a voltage of only 20 V, without tuning the bandgap. The underlying mechanism is the field-induced change in the order parameter of the fluorescent dye in the liquid crystal. The orientation of the transition dipole moment determines the polarization state of the dye emission, thereby promoting lasing in the bandedge mode that favors the emission polarization. Moreover, the dynamic mode-selection capability is retained upon polymer-stabilizing the chiral nematic liquid crystal laser. In the polymer-stabilized system, greatly improved stability and lasing performance are observed. The lasing behavior in chiral nematic liquid crystals (CLC) has been extensively studied over the past decades due to its favorable properties, such as low threshold, high tunability, and the ease of fabrication. [1][2][3] CLC is a particular class of liquid crystals in which the molecules self-assemble into one-dimensional helices, typically formed by mixing a nematic liquid crystal with a chiral agent. The concentration and twisting power of the chiral agent determine the helical pitch (p). Such a periodic chiral structure can be regarded as a one-dimensional photonic crystal for a circularly polarized probe with the same handedness as that of the structure. The associated photonic bandgap (PBG) is located at λ c = n c ⋅p with a bandwidth Δλ = Δn⋅p, where n c and Δn are the average refractive index and birefringence of the CLC, respectively. Resonances occur at the two bandedges: long wavelength edge (LWE) and short wavelength edge (SWE); the corresponding wavelengths are λ LWE = n e ⋅p and λ SWE = n o ⋅p, respectively, where n e is the extraordinary refractive index and n o is the ordinary refractive index. At the bandedge, the group velocity of light approaches zero, and hence the density of states is significantly enhanced. 4,5 In the presence of a gain medium, laser action can occur at the photonic bandedge(s) through optical excitation-usually termed the bandedge lasing. To date, a great deal of effort has been devoted to achieve a wide dynamic tuning range of the lasing wavelength with the aid of external inputs, such as electric field 6,7 , heat 8,9 , light 10 , and mechanical stress 11 . However, the post-

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Tunable lasing in cholesteric liquid crystal elastomers with accurate measurements of strain

Cited by 75 publications

References 29 publications

Facile Anisotropic Deswelling Method for Realizing Large‐Area Cholesteric Liquid Crystal Elastomers with Uniform Structural Color and Broad‐Range Mechanochromic Response

Facile Anisotropic Deswelling Method for Realizing Large‐Area Cholesteric Liquid Crystal Elastomers with Uniform Structural Color and Broad‐Range Mechanochromic Response

Easily Processable and Programmable Responsive Semi‐Interpenetrating Liquid Crystalline Polymer Network Coatings with Changing Reflectivities and Surface Topographies

Electrically assisted bandedge mode selection of photonic crystal lasing in chiral nematic liquid crystals

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