Micron Technology Inc., 2602 Clover Basin Drive, Longmont, Colorado 80503, USA.
J Am Chem Soc. 2012 Oct 3;134(39):16298-306. doi: 10.1021/ja3062826. Epub 2012 Sep 18.
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.
一种沿其极轴掺入强生色团的横向偶氮桥联三聚体铁电液晶（FLC）通过偏光显微镜、差示扫描量热法、二维 X 射线衍射分析、电光测量和非线性光学（NLO）研究进行了合成和表征。这种介晶表现出热力学稳定的各向异性 SmC相和在具有书架几何形状的表面稳定化池中的双稳态铁电开关。它给出了共振增强的 d(22)系数为 28 pm V(-1)（λ = 1.369 μm），用于二次谐波产生（SHG），这是迄今为止所有 FLC 报告的最大 NLO 灵敏度。在同一波长下，确定了一种由螺旋 SmC结构辅助的新型螺旋相匹配。当二次谐波波长为 780nm 远离共振波长（λ(max) = 572nm）时，d(22)系数减小至 6.8 pm V(-1)（λ = 1.56μm）。除了强 SHG 活性外，三聚体还表现出强三倍频产生（THG），估计三阶非线性灵敏度为 χ((3)) = ~3 × 10(-11) esu（λ = 1.56μm），这是从液体晶体的 THG 测量中报告的最大 χ((3))值之一。这项工作使 FLC 在非线性光学中的应用成为可能，并提供了一种开发具有更大 NLO 强度的新型 FLC 的创新方法。
