Optical vortices,a type of structured beam with helical phase wavefronts and‘doughnut’-shaped intensity distributions,have been used to fabricate chiral structures in metals and spiral patterns in anisotropic polari...Optical vortices,a type of structured beam with helical phase wavefronts and‘doughnut’-shaped intensity distributions,have been used to fabricate chiral structures in metals and spiral patterns in anisotropic polarization-dependent azobenzene polymers.However,in isotropic polymers,the fabricated microstructures are typically confined to non-chiral cylindrical geometry due to the two-dimensional‘doughnut’-shaped intensity profile of the optical vortices.Here we develop a powerful strategy to realize chiral microstructures in isotropic material by coaxial interference of a vortex beam and a plane wave,which produces threedimensional(3D)spiral optical fields.These coaxial interference beams are generated by designing contrivable holograms consisting of an azimuthal phase and an equiphase loaded on a liquid-crystal spatial light modulator.In isotropic polymers,3D chiral microstructures are achieved under illumination using coaxial interference femtosecond laser beams with their chirality controlled by the topological charge.Our further investigation reveals that the spiral lobes and chirality are caused by interfering patterns and helical phase wavefronts,respectively.This technique is simple,stable and easy to perform,and it offers broad applications in optical tweezers,optical communications and fast metamaterial fabrication.展开更多
By allowing almost arbitrary distributions of amplitude and phase of electromagnetic waves to be generated by a layer of sub-wavelength-size unit cells,metasurfaces have given rise to the field of meta-holography.Howe...By allowing almost arbitrary distributions of amplitude and phase of electromagnetic waves to be generated by a layer of sub-wavelength-size unit cells,metasurfaces have given rise to the field of meta-holography.However,holography with circularly polarized waves remains complicated as the achiral building blocks of existing meta-holograms inevitably contribute to holographic images generated by both left-handed and right-handed waves.Here we demonstrate how planar chirality enables the fully independent realization of high-efficiency meta-holograms for one circular polarization or the other.Such circular-polarization-selective meta-holograms are based on chiral building blocks that reflect either left-handed or right-handed circularly polarized waves with an orientation-dependent phase.Using terahertz waves,we experimentally demonstrate that this allows the straightforward design of reflective phase meta-holograms,where the use of alternating structures of opposite handedness yields independent holographic images for circularly polarized waves of opposite handedness with negligible polarization cross-talk.展开更多
采用基于密度泛函理论的B3LYP方法和微扰论的MP2方法,研究了单体缬氨酸分子的手性转变机理及水分子和羟基自由基对氢迁移反应的催化作用。反应通道研究发现:缬氨酸手性对映体转变反应有a、b、c和d四个通道。a和c是手性C碳上的H分别以氨...采用基于密度泛函理论的B3LYP方法和微扰论的MP2方法,研究了单体缬氨酸分子的手性转变机理及水分子和羟基自由基对氢迁移反应的催化作用。反应通道研究发现:缬氨酸手性对映体转变反应有a、b、c和d四个通道。a和c是手性C碳上的H分别以氨基N和羰基O为桥,迁移到手性碳的另一侧,实现手性转变;b是手性碳上的H依次以羰基O和氨基N为桥,迁移到手性碳另一侧,实现手性转变;d手性碳上的H以羟基O为桥,迁移到手性C的另一侧,实现手性转变。势能面计算表明:a为最具优势反应通道,最高能垒为257.6k J·mol-1;1个水分子、2个水分子链以及1个水分子和羟基自由基构成的链对H迁移反应有较好的催化作用,使a通到上的高能垒分别降为160.3、124.4和104.0 k J·mol-1。结果表明:缬氨酸分子在生命体内的旋光异构主要是在水分子和羟基自由基共同作用下完成的。展开更多
The effects of two geometric refinement strategies widespread in natural structures, chirality and self-similar hierarchy, on the in-plane elastic response of two-dimensional honeycombs were studied systematically. Si...The effects of two geometric refinement strategies widespread in natural structures, chirality and self-similar hierarchy, on the in-plane elastic response of two-dimensional honeycombs were studied systematically. Simple closed-form expressions were derived for the elastic moduli of several chiral, anti- chiral, and hierarchical honeycombs with hexagon and square based networks. Finite element analysis was employed to validate the analytical estimates of the elastic moduli. The results were also compared with the numerical and experimental data available in the literature. We found that introducing a hier- archical refinement increases the Young＇s modulus of hexagon based honeycombs while decreases their shear modulus. For square based honeycombs, hierarchy increases the shear modulus while decreasing their Young＇s modulus. Introducing chirality was shown to always decrease the Young＇s modulus and Poisson＇s ratio of the structure. However, chirality remains the only route to auxeticity. In particular, we found that anti-tetra-chiral structures were capable of simultaneously exhibiting anisotropy, auxeticity, and remarkably low shear modulus as the magnitude of the chirality of the unit cell increases.展开更多
基金supported by National Natural Science Foundation of China(no.51675503,61475149,51405464,61675190 and 51605463)the Fundamental Research Funds for the Central Universities(no.WK2480000002)+2 种基金the China Postdoctoral Science Foundation(no.2016M590578 and 2016M602027)the Chinese Academy of Sciences Instrument Project(YZ201566)the‘Chinese Thousand Young Talents Program’.
文摘Optical vortices,a type of structured beam with helical phase wavefronts and‘doughnut’-shaped intensity distributions,have been used to fabricate chiral structures in metals and spiral patterns in anisotropic polarization-dependent azobenzene polymers.However,in isotropic polymers,the fabricated microstructures are typically confined to non-chiral cylindrical geometry due to the two-dimensional‘doughnut’-shaped intensity profile of the optical vortices.Here we develop a powerful strategy to realize chiral microstructures in isotropic material by coaxial interference of a vortex beam and a plane wave,which produces threedimensional(3D)spiral optical fields.These coaxial interference beams are generated by designing contrivable holograms consisting of an azimuthal phase and an equiphase loaded on a liquid-crystal spatial light modulator.In isotropic polymers,3D chiral microstructures are achieved under illumination using coaxial interference femtosecond laser beams with their chirality controlled by the topological charge.Our further investigation reveals that the spiral lobes and chirality are caused by interfering patterns and helical phase wavefronts,respectively.This technique is simple,stable and easy to perform,and it offers broad applications in optical tweezers,optical communications and fast metamaterial fabrication.
基金supported by the National Natural Science Foundation of China(grant nos.61422509,61307125,61427814,61420106006,and 61328503)the National Key Basic Research Special Foundation of China(grant no.2014CB339800)+2 种基金the Program for Changjiang Scholars and Innovative Research Team in Universities(grant no.IRT13033)the UK’s Engineering and Physical Sciences Research Council(grant no.EP/M009122/1)the US National Science Foundation(grant no.ECCS-1232081)。
文摘By allowing almost arbitrary distributions of amplitude and phase of electromagnetic waves to be generated by a layer of sub-wavelength-size unit cells,metasurfaces have given rise to the field of meta-holography.However,holography with circularly polarized waves remains complicated as the achiral building blocks of existing meta-holograms inevitably contribute to holographic images generated by both left-handed and right-handed waves.Here we demonstrate how planar chirality enables the fully independent realization of high-efficiency meta-holograms for one circular polarization or the other.Such circular-polarization-selective meta-holograms are based on chiral building blocks that reflect either left-handed or right-handed circularly polarized waves with an orientation-dependent phase.Using terahertz waves,we experimentally demonstrate that this allows the straightforward design of reflective phase meta-holograms,where the use of alternating structures of opposite handedness yields independent holographic images for circularly polarized waves of opposite handedness with negligible polarization cross-talk.
文摘采用基于密度泛函理论的B3LYP方法和微扰论的MP2方法,研究了单体缬氨酸分子的手性转变机理及水分子和羟基自由基对氢迁移反应的催化作用。反应通道研究发现:缬氨酸手性对映体转变反应有a、b、c和d四个通道。a和c是手性C碳上的H分别以氨基N和羰基O为桥,迁移到手性碳的另一侧,实现手性转变;b是手性碳上的H依次以羰基O和氨基N为桥,迁移到手性碳另一侧,实现手性转变;d手性碳上的H以羟基O为桥,迁移到手性C的另一侧,实现手性转变。势能面计算表明:a为最具优势反应通道,最高能垒为257.6k J·mol-1;1个水分子、2个水分子链以及1个水分子和羟基自由基构成的链对H迁移反应有较好的催化作用,使a通到上的高能垒分别降为160.3、124.4和104.0 k J·mol-1。结果表明:缬氨酸分子在生命体内的旋光异构主要是在水分子和羟基自由基共同作用下完成的。
基金made possible by a NPRP award(NPRP 7-882-2-326)from the Qatar National Research Fund(a member of the Qatar Foundation)
文摘The effects of two geometric refinement strategies widespread in natural structures, chirality and self-similar hierarchy, on the in-plane elastic response of two-dimensional honeycombs were studied systematically. Simple closed-form expressions were derived for the elastic moduli of several chiral, anti- chiral, and hierarchical honeycombs with hexagon and square based networks. Finite element analysis was employed to validate the analytical estimates of the elastic moduli. The results were also compared with the numerical and experimental data available in the literature. We found that introducing a hier- archical refinement increases the Young＇s modulus of hexagon based honeycombs while decreases their shear modulus. For square based honeycombs, hierarchy increases the shear modulus while decreasing their Young＇s modulus. Introducing chirality was shown to always decrease the Young＇s modulus and Poisson＇s ratio of the structure. However, chirality remains the only route to auxeticity. In particular, we found that anti-tetra-chiral structures were capable of simultaneously exhibiting anisotropy, auxeticity, and remarkably low shear modulus as the magnitude of the chirality of the unit cell increases.
