Ferroelectric Liquid Crystals for Nonlinear Optical Applications

Zhang, Yongqiang; Etxebarría, J.

doi:10.1002/9781118259993.ch4

Cited by 10 publications

(9 citation statements)

References 149 publications

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“…Hence both qualitative and quantitative SHG experiments have been widely applied to liquid crystal research and development. 5,7,8 The polar direction in an FLC can be electrically controlled by switching between two ferroelectric states, enabling fabrication of more complex NLO devices. Helicoidal structures in a FLC provide a special way for phase matching (PM) during an SHG process, 9 and unwinding/winding such structures using an electric field (E-field) permits to obtain SHG switching.…”

Section: ■ Introductionmentioning

confidence: 99%

“…To enable viable NLO applications of an FLC, incorporating a strong chromophore with a large hyperpolarizability (β) along the FLC's polar axis is a prerequisite. 5 Although numerous strong NLO chromophores have been developed for poled polymers, 11 realizing such a goal with liquid crystals is still very challenging because in most cases the required SmC* phase is killed upon incorporating a big chromophore into a rod-shaped FLC along its polar axis. Consequently, the size of NLO coefficients for FLCs has been insufficient for decades.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Ferroelectric liquid crystals (FLCs), as a special type of organic NLO material, will become a compelling alternative to inorganic crystals and/or electrically poled organic glasses (i.e., poled polymers) if large NLO strength is achieved. , Since FLCs possess thermodynamically stable polar order from self-assembled tilted smectic layer structures, they are inherently suitable for second harmonic generation (SHG). Hence both qualitative and quantitative SHG experiments have been widely applied to liquid crystal research and development. ,, The polar direction in an FLC can be electrically controlled by switching between two ferroelectric states, enabling fabrication of more complex NLO devices.…”

Section: Introductionmentioning

confidence: 99%

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An Azo-Bridged Ferroelectric Liquid Crystal with Highly Enhanced Second and Third Harmonic Generation

Zhang

Ortega²,

Baumeister

et al. 2012

J. Am. Chem. Soc.

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A laterally azo-bridged trimer ferroelectric liquid crystal (FLC) incorporating a strong chromophore along its polar axis was synthesized and characterized by polarized-light optical microscopy, differential scanning calorimetry, two-dimensional X-ray diffraction analysis, electro-optical measurements, and nonlinear optical (NLO) investigations. This mesogen exhibits a thermodynamically stable enantiotropic SmC* phase and a bistable ferroelectric switching in a surface stabilized cell with bookshelf geometry. It gives the resonance-enhanced d(22) coefficient of 28 pm V(-1) (λ = 1.369 μm) for second harmonic generation (SHG), the largest NLO susceptibility reported to date for all FLCs. At the same wavelength, a new type of helicoidal phase matching assisted by the helical SmC* structure was identified. When the second harmonic wavelength of 780 nm is far away from the resonance wavelength (λ(max) = 572 nm), the d(22) coefficient is reduced to 6.8 pm V(-1) (λ = 1.56 μm). In addition to a strong SHG activity, the trimer also shows a strong third harmonic generation (THG) with an estimated third-order nonlinear susceptibility of χ((3)) = ~3 × 10(-11) esu (λ = 1.56 μm), among the largest χ((3)) value reported from THG measurements for liquid crystals. This work enables viable applications of FLCs in nonlinear optics and offers an innovative approach to develop new FLCs with larger NLO strength.

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Section: ■ Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

An Azo-Bridged Ferroelectric Liquid Crystal with Highly Enhanced Second and Third Harmonic Generation

Zhang

Ortega²,

Baumeister

et al. 2012

J. Am. Chem. Soc.

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“…The nonlinear optical (NLO) application of bent-core molecules has been previously reviewed in great detail [31,178]. The advancement of this area is summarized in this section.…”

Section: Nonlinear Opticsmentioning

confidence: 99%

Electric‐ and Light‐Responsive Bent‐Core Liquid Crystals: From Molecular Architecture and Supramolecular Nanostructures to Applications

Zhang¹

2013

Intelligent Stimuli‐Responsive Materials

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The three classic states of matter are well known and ubiquitous in everyday life: solid, liquid, and gas. Liquid crystals (LCs), an intermediate state between solid crystal and isotropic liquid, constitute a new fascinating class of condensed soft matter uniquely combining both fluidity and long-range order. The fluid-like mobility enables LCs to be switchable under external stimuli, and crystal-like long-range order bestows anisotropic physical properties on LCs. LCs can be divided into two main classes: thermotropic and lyotropic. Thermotropic LCs consist of individual molecules (or ion pairs) and exhibit phase transitions with the change of temperature. In this case, temperature is the fundamental thermodynamic factor determining mesophase formation. Lyotropic LCs are a special type of solution system that can form mesophases as a function of both temperature and concentration of LC molecules. The building block of a lyotropic phase is an aggregate (called a micelle) formed via self-assembly of many molecules (typically on the order of 100). Examples of LCs can be found both in the natural world and in technological applications. Thermotropic LCs find 189 190 ELECTRIC-AND LIGHT-RESPONSIVE BENT-CORE LIQUID CRYSTALS a wide variety of uses in displays, and an important example of lyotropic LCs is cell membranes formed by amphiphilic lipids. Surfactants in water (i.e., soap water) constitute another useful example of lyotropic LCs. Although the majority of LCs are organic molecules, there exist many LC materials incorporating metals into organic anisotropic molecules [1-3]. These organic-inorganic hybrid LC materials are described as metallomesogens and are recently called metallotropic LCs [4] as distinguished from two main LC classes. In fact, metallomesogens can be classified as either thermotropic or lyotropic LCs depending on their composition and conditions. However, it should be noted that metallomesogens offer a material platform to incorporate magnetic, electronic, optical, redox, and catalytic properties common to inorganic materials into LCs.Although thermotropic LCs have been known to scientists for over 100 years since a discovery by the Austrian botanical physiologist Friedrich Reintizer in 1888, it was only in the late 1960s that they began to be used in display applications. Today, they are best known for their exceptionally successful commercial applications in flat panel display products such as TVs, smart phones, computer displays, and digital projectors. Although today's LC display technology is becoming very advanced, LC materials used in display devices possess the simplest nematic (N) phase and their molecules have been variants on simple rod shapes (Fig. 6.1a). Besides nematic phases, LCs can exhibit other phases: smectic (Sm), columnar (Col), and cubic phases, depending on the orientational or positional orders of their molecules. Nematic phases have only long-range orientational order, smectic mesophases exhibit one-dimensional (1D) positional order and form two-dimensional (2D) layered ...

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“…It is well known that ferroelectric liquid crystals (FLCs) are potentially attractive materials from the viewpoint of nonlinear optics [1]. FLCs with a large second-order susceptibility are a compelling alternative to inorganic and poled-polymer compounds since they offer important advantages.…”

Section: Introductionmentioning

confidence: 99%

Second-harmonic generation in a laterally azo-bridged trimer ferroelectric liquid crystal: Phase matching in the presence of a helicoidal structure

et al. 2012

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Optical second-harmonic generation (SHG) has been studied in a trimer smectic C* liquid crystal especially designed for nonlinear optical applications. The molecule has a long conjugated donor-acceptor unit that transversally links three parallel rod-shaped moieties. A strong SHG signal has been observed at a fundamental wavelength of 1369 nm even in the presence of the spontaneous helicoidal structure of the smectic C* phase.This unusual behavior has been interpreted as due to the existence of a phase matching, in which the wave vector mismatch is compensated by the wave vector of the helix. This point has been confirmed by the study of the SHG intensity versus sample thickness and light polarization characteristics. The main coefficient of the second-order susceptibility tensor of the material has been estimated to be d 22 =28 pm/V.

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Ferroelectric Liquid Crystals for Nonlinear Optical Applications

Cited by 10 publications

References 149 publications

An Azo-Bridged Ferroelectric Liquid Crystal with Highly Enhanced Second and Third Harmonic Generation

An Azo-Bridged Ferroelectric Liquid Crystal with Highly Enhanced Second and Third Harmonic Generation

Electric‐ and Light‐Responsive Bent‐Core Liquid Crystals: From Molecular Architecture and Supramolecular Nanostructures to Applications

Second-harmonic generation in a laterally azo-bridged trimer ferroelectric liquid crystal: Phase matching in the presence of a helicoidal structure

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