Manipulating directional chiral optical emissions on a nanometer scale is significant for material science research. The electron-beam-excited nanoantenna provides a favorable platform to tune optical emissions at the...Manipulating directional chiral optical emissions on a nanometer scale is significant for material science research. The electron-beam-excited nanoantenna provides a favorable platform to tune optical emissions at the deep subwavelength scale. Here we present an L-shaped electron-beam-excited nanoantenna(LENA) with two identical orthogonal arms. By selecting different electron-beam impacting sites on the LENA, either the lefthanded circularly polarized(LCP) or the right-handed circularly polarized(RCP) emission can be excited. The LCP and RCP emissions possess different emission directionality, and the emission wavelength depends on the arm length of the LENA. Further, we show a combined nanoantenna with two LENAs of different arm lengths.Induced by the electron beam, LCP and RCP lights emit simultaneously from the nanoantenna with different wavelengths to different directions. This approach is suggested to be informative for investigating electron-photon interaction and electron-beam spectroscopy in nanophotonics.展开更多
The Brewster’s law predicts zero reflection of p-polarization on a dielectric surface at a particular angle.However,when loss is introduced into the permittivity of the dielectric,the Brewster condition breaks down a...The Brewster’s law predicts zero reflection of p-polarization on a dielectric surface at a particular angle.However,when loss is introduced into the permittivity of the dielectric,the Brewster condition breaks down and reflection unavoidably appears.In this work,we found an exception to this long-standing dilemma by creating a class of nonmagnetic anisotropic metamaterials,where anomalous Brewster effects with independently tunable absorption and refraction emerge.This loss-independent Brewster effect is bestowed by the extra degrees of freedoms introduced by anisotropy and strictly protected by the reciprocity principle.The bandwidth can cover an extremely wide spectrum from dc to optical frequencies.Two examples of reflectionless Brewster absorbers with different Brewster angles are both demonstrated to achieve large absorbance in a wide spectrum via microwave experiments.Our work extends the scope of Brewster effect to the horizon of nonmagnetic absorptive materials,which promises an unprecedented wide bandwidth for reflectionless absorption with high efficiency.展开更多
Deep-subwavelength all-dielectric composite materials are believed to tightly obey the Maxwell Garnett effective medium theory. Here, we demonstrate that the Maxwell Garnett theory could break down due to evanescent f...Deep-subwavelength all-dielectric composite materials are believed to tightly obey the Maxwell Garnett effective medium theory. Here, we demonstrate that the Maxwell Garnett theory could break down due to evanescent fields in deep-subwavelength dielectric structures. By using two-and three-dimensional dielectric composite materials with inhomogeneities at a scale of λ∕100, we show that local evanescent fields generally occur near the dielectric inhomogeneities. When tiny absorptive constituents are placed there, the absorption and transmission of the whole composite will show strong dependence on the positions of the absorptive constituents. The Maxwell Garnett theory fails to predict such position-dependent characteristics because it averages out the evanescent fields. By taking the distribution of the evanescent fields into consideration, we have made a correction to the Maxwell Garnett theory so that the position-dependent characteristics become predictable. We reveal not only the breakdown of the Maxwell Garnett theory, but also a unique phenomenon of "invisible" loss induced by the prohibition of electric fields at deep-subwavelength scales. We believe our work promises a route to control the macroscopic properties of composite materials without changing their composition, which is beyond the traditional Maxwell Garnett theory.展开更多
Conventional dielectric solid materials,both natural and artifcial,lack electromagnetic self-duality and thus require additional coatings to achieve impedance matching with free space.Here,we present a class of dielec...Conventional dielectric solid materials,both natural and artifcial,lack electromagnetic self-duality and thus require additional coatings to achieve impedance matching with free space.Here,we present a class of dielectric metamaterials that are effectively self-dual and vacuum-like,thereby exhibiting full-polarization omnidirectional impedance matching as an unusual Brewster effect extended across all incident angles and polarizations.With both birefringence and reflection eliminated regardless of wavefront and polarization,such anisotropic metamaterials could establish the electromagnetic equivalence with"stretched free space"in transformation optics,as substantiated through full-wave simulations and microwave experiments.Our findings open a practical pathway for realizing unprecedented polarization-independence and omnidirectional impedance-matching characteristics in pure dielectric solids.展开更多
基金supported by the National Key R&D Program of China(Grant No.2020YFA0211300)the National Natural Science Foundation of China(Grant Nos.11974177,61975078,and 12234010)。
文摘Manipulating directional chiral optical emissions on a nanometer scale is significant for material science research. The electron-beam-excited nanoantenna provides a favorable platform to tune optical emissions at the deep subwavelength scale. Here we present an L-shaped electron-beam-excited nanoantenna(LENA) with two identical orthogonal arms. By selecting different electron-beam impacting sites on the LENA, either the lefthanded circularly polarized(LCP) or the right-handed circularly polarized(RCP) emission can be excited. The LCP and RCP emissions possess different emission directionality, and the emission wavelength depends on the arm length of the LENA. Further, we show a combined nanoantenna with two LENAs of different arm lengths.Induced by the electron beam, LCP and RCP lights emit simultaneously from the nanoantenna with different wavelengths to different directions. This approach is suggested to be informative for investigating electron-photon interaction and electron-beam spectroscopy in nanophotonics.
基金Y.L.,R.P.,and M.W.acknowledge support from the National Key R&D Program of China under Grant No.2020YFA0211300,2017YFA0303702National Natural Science Foundation of China under Grant Nos.11974176,11634005,11974177,61975078+3 种基金J.Luo acknowledges support from the National Natural Science Foundation of China under Grant No.11704271Natural Science Foundation of Jiangsu Province under Grant No.BK20170326a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)J.Li acknowledges support from the Research Grants Council of Hong Kong under Grant No.R6015-18.
文摘The Brewster’s law predicts zero reflection of p-polarization on a dielectric surface at a particular angle.However,when loss is introduced into the permittivity of the dielectric,the Brewster condition breaks down and reflection unavoidably appears.In this work,we found an exception to this long-standing dilemma by creating a class of nonmagnetic anisotropic metamaterials,where anomalous Brewster effects with independently tunable absorption and refraction emerge.This loss-independent Brewster effect is bestowed by the extra degrees of freedoms introduced by anisotropy and strictly protected by the reciprocity principle.The bandwidth can cover an extremely wide spectrum from dc to optical frequencies.Two examples of reflectionless Brewster absorbers with different Brewster angles are both demonstrated to achieve large absorbance in a wide spectrum via microwave experiments.Our work extends the scope of Brewster effect to the horizon of nonmagnetic absorptive materials,which promises an unprecedented wide bandwidth for reflectionless absorption with high efficiency.
基金National Key Research and Development Program of China(2017YFA0303702)National Natural Science Foundation of China(11704271,11974176,61671314)+1 种基金Natural Science Foundation of Jiangsu Province(BK20170326)Priority Academic Program Development of Jiangsu Higher Education Institutions。
文摘Deep-subwavelength all-dielectric composite materials are believed to tightly obey the Maxwell Garnett effective medium theory. Here, we demonstrate that the Maxwell Garnett theory could break down due to evanescent fields in deep-subwavelength dielectric structures. By using two-and three-dimensional dielectric composite materials with inhomogeneities at a scale of λ∕100, we show that local evanescent fields generally occur near the dielectric inhomogeneities. When tiny absorptive constituents are placed there, the absorption and transmission of the whole composite will show strong dependence on the positions of the absorptive constituents. The Maxwell Garnett theory fails to predict such position-dependent characteristics because it averages out the evanescent fields. By taking the distribution of the evanescent fields into consideration, we have made a correction to the Maxwell Garnett theory so that the position-dependent characteristics become predictable. We reveal not only the breakdown of the Maxwell Garnett theory, but also a unique phenomenon of "invisible" loss induced by the prohibition of electric fields at deep-subwavelength scales. We believe our work promises a route to control the macroscopic properties of composite materials without changing their composition, which is beyond the traditional Maxwell Garnett theory.
基金the National Key R&D Program of China(Grants Nos.2022YFA1404303,2020YFA0211300)the National Natural Science Foundation of China(Grants Nos.12174188,11974176,12474293,12374293,12234010,11874286)Natural Science Foundation of Jiangsu Province(Grant No.BK20221354).
文摘Conventional dielectric solid materials,both natural and artifcial,lack electromagnetic self-duality and thus require additional coatings to achieve impedance matching with free space.Here,we present a class of dielectric metamaterials that are effectively self-dual and vacuum-like,thereby exhibiting full-polarization omnidirectional impedance matching as an unusual Brewster effect extended across all incident angles and polarizations.With both birefringence and reflection eliminated regardless of wavefront and polarization,such anisotropic metamaterials could establish the electromagnetic equivalence with"stretched free space"in transformation optics,as substantiated through full-wave simulations and microwave experiments.Our findings open a practical pathway for realizing unprecedented polarization-independence and omnidirectional impedance-matching characteristics in pure dielectric solids.
