Plasmonic vortices confining orbital angular momentums to surface have aroused wide research interest in the last decade.Recent advances of near-field microscopes have enabled the study on the spatiotemporal dynamics ...Plasmonic vortices confining orbital angular momentums to surface have aroused wide research interest in the last decade.Recent advances of near-field microscopes have enabled the study on the spatiotemporal dynamics of plasmonic vortices,providing a better understanding of optical orbital angular momentums in the evanescent wave regime.However,these works only focused on the objective characterization of plasmonic vortex and have not achieved subjectively tailoring of its spatiotemporal dynamics for specific applications.Herein,it is demonstrated that the plasmonic vortices with the same topological charge can be endowed with distinct spatiotemporal dynamics by simply changing the coupler design.Based on a near-field scanning terahertz microscopy,the surface plasmon fields are directly obtained with ultrahigh spatiotemporal resolution,experimentally exhibiting the generation and evolution divergences during the whole lifetime of plasmonic vortices.The proposed strategy is straightforward and universal,which can be readily applied into visible or infrared frequencies,facilitating the development of plasmonic vortex related researches and applications.展开更多
Metamaterials composed of metallic antennae arrays are used as they possess extraordinary optical transmission(EOT)in the terahertz(THz)region,whereby a giant forward light propagation can be created using constructiv...Metamaterials composed of metallic antennae arrays are used as they possess extraordinary optical transmission(EOT)in the terahertz(THz)region,whereby a giant forward light propagation can be created using constructive interference of tunneling surface plasmonic waves.However,numerous applications of THz meta-devices demand an active manipula-tion of the THz beam in free space.Although some studies have been carried out to control the EOT for the THz region,few of these are based upon electrical modulation of the EOT phenomenon,and novel strategies are required for act-ively and dynamically reconfigurable EOT meta-devices.In this work,we experimentally present that the EOT resonance can be coupled to optically reconfigurable chalcogenide metamaterials which offers a reversible all-optical control of the THz light.A modulation efficiency of 88%in transmission at 0.85 THz is experimentally observed using the EOT metama-terials,which is composed of a gold(Au)circular aperture array sitting on a non-volatile chalcogenide phase change ma-terial(Ge2Sb2Te5)film.This comes up with a robust and ultrafast reconfigurable EOT over 20 times of switching,excited by a nanosecond pulsed laser.The measured data have a good agreement with finite-element-method numerical simula-tion.This work promises THz modulators with significant on/off ratios and fast speeds.展开更多
Graphene has been recognized as a promising candidate in developing tunable terahertz(THz)functional devices due to its excellent optical and electronic properties,such as high carrier mobility and tunable conductivit...Graphene has been recognized as a promising candidate in developing tunable terahertz(THz)functional devices due to its excellent optical and electronic properties,such as high carrier mobility and tunable conductivity.Here,we review graphene-based THz modulators we have recently developed.First,the optical properties of graphene are discussed.Then,graphene THz modulators realized by different methods,such as gate voltage,optical pump,and nonlinear response of graphene are presented.Finally,challenges and prospective of graphene THz modulators are also discussed.展开更多
High-performance terahertz(THz)devices with reconfigurable features are highly desirable in many promising THz applications.However,most of the existing reconfigurable THz elements are still limited to volatile respon...High-performance terahertz(THz)devices with reconfigurable features are highly desirable in many promising THz applications.However,most of the existing reconfigurable THz elements are still limited to volatile responses,single functionality,and time-consuming multistep manufacturing procedures.In this paper,we report a lithography-free approach to create reconfigurable and nonvolatile THz components by exploring the reversible,nonvolatile,and continuous THz modulation capability of the phase change material Ge_(2)Sb_(2)Te_(5).As a proof of concept,THz gratings with significant Rayleigh anomalies and diffraction as well as ultrathin THz flat lenses with subwavelength and ultra-broadband focusing capabilities are designed and fabricated on ultrathin Ge_(2)Sb_(2)Te_(5)films using the presented photo-imprint strategy.Moreover,such a method can also be adopted to create more complex THz devices,such as Pancharatnam–Berry phase metasurfaces and grayscale holographic plates.With these findings,the proposed method will provide a promising solution to realize reconfigurable and nonvolatile THz elements.展开更多
Radiation at terahertz frequencies can be used to analyze the structural dynamics of water and biomolecules,but applying the technique to aqueous solutions and tissues remains challenging since terahertz radiation is ...Radiation at terahertz frequencies can be used to analyze the structural dynamics of water and biomolecules,but applying the technique to aqueous solutions and tissues remains challenging since terahertz radiation is strongly absorbed by water.While this absorption enables certain analyses,such as the structure of water and its interactions with biological solutes,it limits the thickness of samples that can be analyzed,and it drowns out weaker signals from biomolecules of interest.We present a method for analyzing water-rich samples via time-domain terahertz optoacoustics over a 104-fold thickness ranging from microns to centimeters.We demonstrate that adjusting the temperature to alter the terahertz optoacoustic(THz-OA)signal of water improves the sensitivity with which it can be analyzed and,conversely,can reduce or even“silence”its signal.Temperature-manipulated THz-OA signals of aqueous solutions allow detection of solutes such as ions with an order of magnitude greater sensitivity than terahertz time-domain spectroscopy,and potentially provide more characteristic parameters related to both terahertz absorption and ultrasonic propagation.Terahertz optoacoustics may be a powerful tool for spectroscopy and potential imaging of aqueous solutions and tissues to explore molecular interactions and biochemical processes.展开更多
Metasurfaces,especially tunable ones,have played a major role in controlling the amplitude,phase,and polarization of electromagnetic waves and attracted growing interest,with a view toward a new generation of miniatur...Metasurfaces,especially tunable ones,have played a major role in controlling the amplitude,phase,and polarization of electromagnetic waves and attracted growing interest,with a view toward a new generation of miniaturized devices.However,to date,most existing reconfigurable devices are bounded in volatile nature with sustained external energy to maintain and single functionality,which restrict their further applications.Here,we demonstrate for the first time,to our knowledge,nonvolatile,reconfigurable,and dynamic Janus metasurfaces by incorporating phase-change material Ge_(2)Se_(2)Te_(5)(GST)in the terahertz(THz)regime.First,we experimentally show the reversible switching characteristic of GST on large areas by applying a single nanosecond laser pulse,which exhibits excellent contrast of THz properties in both states.Then,we present a multiplex metasurface scheme.In each metasurface,three sets of structures are adopted,in which two sets integrate GST.The effective structures can be reversely modulated by the amorphization and crystallization of GST.As a proof of concept,the dynamic beam splitter,bifocal metalens,dual-mode focusing optical vortex generators,and switchable metalens/focusing optical vortex generators are designed,fabricated,and experimentally characterized,and can be switched reversibly and repeatedly with the help of optical and thermal stimuli.Our scheme will pave the way toward the development of multifunctional and compact THz devices and may find use for applications in THz imaging,sensing,and communications.展开更多
Polarization manipulation is essential in developing cutting-edge photonic devices ranging from optical communication displays to solar energy harvesting. Most previous works for efficient polarization control cannot ...Polarization manipulation is essential in developing cutting-edge photonic devices ranging from optical communication displays to solar energy harvesting. Most previous works for efficient polarization control cannot avoid utilizing metallic components that inevitably suffer from large ohmic loss and thus low operational efficiency.Replacing metallic components with Mie resonance-based dielectric resonators will largely suppress the ohmic loss toward high-efficiency metamaterial devices. Here, we propose an efficient approach for broadband, highquality polarization rotation operating in transmission mode with all-dielectric metamaterials in the terahertz regime. By separating the orthogonal polarization components in space, we obtain rotated output waves with a conversion efficiency of 67.5%. The proposed polarization manipulation strategy shows impressive robustness and flexibility in designing metadevices of both linear-and circular-polarization incidences.展开更多
Actively controlling the polarization states of terahertz(THz)waves is essential for polarization-sensitive spectroscopy,which has various applications in anisotropy imaging,noncontact Hall measurement,and vibrational...Actively controlling the polarization states of terahertz(THz)waves is essential for polarization-sensitive spectroscopy,which has various applications in anisotropy imaging,noncontact Hall measurement,and vibrational circular dichroism.In the THz regime,the lack of a polarization modulator hinders the development of this spectroscopy.We theoretically and experimentally demonstrate that conjugated bilayer chiral metamaterials(CMMs)integrated with Ge_(2)Sb_(2)Te_(5)(GST225)active components can achieve nonvolatile and continuously tunable optical activity in the THz region.A THz time-domain spectroscopic system was used to characterize the device,showing a tunable ellipticity(from‒36°to 0°)and rotation of the plane polarization(from 32°to 0°)at approximately 0.73 THz by varying the GST225 state from amorphous(AM)to crystalline(CR).Moreover,a continuously tunable chiroptical response was experimentally observed by partially crystallizing the GST225,which can create intermediate states,having regions of both AM and CR states.Note that the GST225 has an advantage of nonvolatility over the other active elements and does not require any energy to retain its structural state.Our work allows the development of THz metadevices capable of actively manipulating the polarization of THz waves and may find applications for dynamically tunable THz circular polarizers and polarization modulators for THz emissions.展开更多
基金supported by the National Natural Science Foundation of China(62005193,62135008,62075158,62025504,61935015)the National Science Foundation(2114103)Guangxi Key Laboratory of Optoelectroric Information Processing(GD20202).
文摘Plasmonic vortices confining orbital angular momentums to surface have aroused wide research interest in the last decade.Recent advances of near-field microscopes have enabled the study on the spatiotemporal dynamics of plasmonic vortices,providing a better understanding of optical orbital angular momentums in the evanescent wave regime.However,these works only focused on the objective characterization of plasmonic vortex and have not achieved subjectively tailoring of its spatiotemporal dynamics for specific applications.Herein,it is demonstrated that the plasmonic vortices with the same topological charge can be endowed with distinct spatiotemporal dynamics by simply changing the coupler design.Based on a near-field scanning terahertz microscopy,the surface plasmon fields are directly obtained with ultrahigh spatiotemporal resolution,experimentally exhibiting the generation and evolution divergences during the whole lifetime of plasmonic vortices.The proposed strategy is straightforward and universal,which can be readily applied into visible or infrared frequencies,facilitating the development of plasmonic vortex related researches and applications.
文摘Metamaterials composed of metallic antennae arrays are used as they possess extraordinary optical transmission(EOT)in the terahertz(THz)region,whereby a giant forward light propagation can be created using constructive interference of tunneling surface plasmonic waves.However,numerous applications of THz meta-devices demand an active manipula-tion of the THz beam in free space.Although some studies have been carried out to control the EOT for the THz region,few of these are based upon electrical modulation of the EOT phenomenon,and novel strategies are required for act-ively and dynamically reconfigurable EOT meta-devices.In this work,we experimentally present that the EOT resonance can be coupled to optically reconfigurable chalcogenide metamaterials which offers a reversible all-optical control of the THz light.A modulation efficiency of 88%in transmission at 0.85 THz is experimentally observed using the EOT metama-terials,which is composed of a gold(Au)circular aperture array sitting on a non-volatile chalcogenide phase change ma-terial(Ge2Sb2Te5)film.This comes up with a robust and ultrafast reconfigurable EOT over 20 times of switching,excited by a nanosecond pulsed laser.The measured data have a good agreement with finite-element-method numerical simula-tion.This work promises THz modulators with significant on/off ratios and fast speeds.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFA0701004)the National Natural Science Founda-tion of China(Grant Nos.61675145,61722509,61735012,and 61420106006).
文摘Graphene has been recognized as a promising candidate in developing tunable terahertz(THz)functional devices due to its excellent optical and electronic properties,such as high carrier mobility and tunable conductivity.Here,we review graphene-based THz modulators we have recently developed.First,the optical properties of graphene are discussed.Then,graphene THz modulators realized by different methods,such as gate voltage,optical pump,and nonlinear response of graphene are presented.Finally,challenges and prospective of graphene THz modulators are also discussed.
基金Key Fund of Shenzhen Natural Science Foundation(JCYJ20200109150212515)Tianjin Municipal Fund for Distinguished Young Scholars(20JCJQJC00190)+1 种基金National Natural Science Foundation of China(62235013)National Key Research and Development Program of China(2017YFA0701004,2019YFA0709100,2020YFA0714504)。
文摘High-performance terahertz(THz)devices with reconfigurable features are highly desirable in many promising THz applications.However,most of the existing reconfigurable THz elements are still limited to volatile responses,single functionality,and time-consuming multistep manufacturing procedures.In this paper,we report a lithography-free approach to create reconfigurable and nonvolatile THz components by exploring the reversible,nonvolatile,and continuous THz modulation capability of the phase change material Ge_(2)Sb_(2)Te_(5).As a proof of concept,THz gratings with significant Rayleigh anomalies and diffraction as well as ultrathin THz flat lenses with subwavelength and ultra-broadband focusing capabilities are designed and fabricated on ultrathin Ge_(2)Sb_(2)Te_(5)films using the presented photo-imprint strategy.Moreover,such a method can also be adopted to create more complex THz devices,such as Pancharatnam–Berry phase metasurfaces and grayscale holographic plates.With these findings,the proposed method will provide a promising solution to realize reconfigurable and nonvolatile THz elements.
基金This work was supported by the National Key Research and Development Program of China(2017YFA0701004)the National Natural Science Foundation of China(61675145,61722509,81771880,61735012,and 61420106006)the Tianjin Municipal Government(19JCQNJC12800).J.L.,Y.X.Y.,and L.W.J.contributed equally to this work.The authors declare no conflicts of interest.
文摘Radiation at terahertz frequencies can be used to analyze the structural dynamics of water and biomolecules,but applying the technique to aqueous solutions and tissues remains challenging since terahertz radiation is strongly absorbed by water.While this absorption enables certain analyses,such as the structure of water and its interactions with biological solutes,it limits the thickness of samples that can be analyzed,and it drowns out weaker signals from biomolecules of interest.We present a method for analyzing water-rich samples via time-domain terahertz optoacoustics over a 104-fold thickness ranging from microns to centimeters.We demonstrate that adjusting the temperature to alter the terahertz optoacoustic(THz-OA)signal of water improves the sensitivity with which it can be analyzed and,conversely,can reduce or even“silence”its signal.Temperature-manipulated THz-OA signals of aqueous solutions allow detection of solutes such as ions with an order of magnitude greater sensitivity than terahertz time-domain spectroscopy,and potentially provide more characteristic parameters related to both terahertz absorption and ultrasonic propagation.Terahertz optoacoustics may be a powerful tool for spectroscopy and potential imaging of aqueous solutions and tissues to explore molecular interactions and biochemical processes.
基金National Key Research and Development Program of China(2017YFA0701004,2019YFA0709100,2020YFA0714504)Tianjin Municipal Fund for Distinguished Young Scholars(20JCJQJC00190)Key Fund of Shenzhen Natural Science Foundation(JCYJ20200109150212515)。
文摘Metasurfaces,especially tunable ones,have played a major role in controlling the amplitude,phase,and polarization of electromagnetic waves and attracted growing interest,with a view toward a new generation of miniaturized devices.However,to date,most existing reconfigurable devices are bounded in volatile nature with sustained external energy to maintain and single functionality,which restrict their further applications.Here,we demonstrate for the first time,to our knowledge,nonvolatile,reconfigurable,and dynamic Janus metasurfaces by incorporating phase-change material Ge_(2)Se_(2)Te_(5)(GST)in the terahertz(THz)regime.First,we experimentally show the reversible switching characteristic of GST on large areas by applying a single nanosecond laser pulse,which exhibits excellent contrast of THz properties in both states.Then,we present a multiplex metasurface scheme.In each metasurface,three sets of structures are adopted,in which two sets integrate GST.The effective structures can be reversely modulated by the amorphization and crystallization of GST.As a proof of concept,the dynamic beam splitter,bifocal metalens,dual-mode focusing optical vortex generators,and switchable metalens/focusing optical vortex generators are designed,fabricated,and experimentally characterized,and can be switched reversibly and repeatedly with the help of optical and thermal stimuli.Our scheme will pave the way toward the development of multifunctional and compact THz devices and may find use for applications in THz imaging,sensing,and communications.
基金Ministry of Science and Technology of the People’s Republic of China(MOST)National Key Research and Development Program of China(2017YFA0701004)+1 种基金National Natural Science Foundation of China(NSFC)(61875150,6142010660,61427814,61605143,61735012)King Abdullah University of Science and Technology(KAUST)(CRF-2016-2950-RG5)
文摘Polarization manipulation is essential in developing cutting-edge photonic devices ranging from optical communication displays to solar energy harvesting. Most previous works for efficient polarization control cannot avoid utilizing metallic components that inevitably suffer from large ohmic loss and thus low operational efficiency.Replacing metallic components with Mie resonance-based dielectric resonators will largely suppress the ohmic loss toward high-efficiency metamaterial devices. Here, we propose an efficient approach for broadband, highquality polarization rotation operating in transmission mode with all-dielectric metamaterials in the terahertz regime. By separating the orthogonal polarization components in space, we obtain rotated output waves with a conversion efficiency of 67.5%. The proposed polarization manipulation strategy shows impressive robustness and flexibility in designing metadevices of both linear-and circular-polarization incidences.
基金the National Key Research and Development Program of China(2019YFA0709100,2020YFA0714504)the LiaoNing Revitalization Talents Program(Grant No.XLYC1807237).
文摘Actively controlling the polarization states of terahertz(THz)waves is essential for polarization-sensitive spectroscopy,which has various applications in anisotropy imaging,noncontact Hall measurement,and vibrational circular dichroism.In the THz regime,the lack of a polarization modulator hinders the development of this spectroscopy.We theoretically and experimentally demonstrate that conjugated bilayer chiral metamaterials(CMMs)integrated with Ge_(2)Sb_(2)Te_(5)(GST225)active components can achieve nonvolatile and continuously tunable optical activity in the THz region.A THz time-domain spectroscopic system was used to characterize the device,showing a tunable ellipticity(from‒36°to 0°)and rotation of the plane polarization(from 32°to 0°)at approximately 0.73 THz by varying the GST225 state from amorphous(AM)to crystalline(CR).Moreover,a continuously tunable chiroptical response was experimentally observed by partially crystallizing the GST225,which can create intermediate states,having regions of both AM and CR states.Note that the GST225 has an advantage of nonvolatility over the other active elements and does not require any energy to retain its structural state.Our work allows the development of THz metadevices capable of actively manipulating the polarization of THz waves and may find applications for dynamically tunable THz circular polarizers and polarization modulators for THz emissions.