In this study,we assess the potential of X-band Interferometric Synthetic Aperture Radar imagery for automated classification of sea ice over the Baltic Sea.A bistatic SAR scene acquired by the TanDEM-X mission over t...In this study,we assess the potential of X-band Interferometric Synthetic Aperture Radar imagery for automated classification of sea ice over the Baltic Sea.A bistatic SAR scene acquired by the TanDEM-X mission over the Bothnian Bay in March of 2012 was used in the analysis.Backscatter intensity,interferometric coherence magnitude,and interferometric phase have been used as informative features in several classification experiments.Various combinations of classification features were evaluated using Maximum likelihood(ML),Random Forests(RF)and Support Vector Machine(SVM)classifiers to achieve the best possible discrimination between open water and several sea ice types(undeformed ice,ridged ice,moderately deformed ice,brash ice,thick level ice,and new ice).Adding interferometric phase and coherence-magnitude to backscatter-intensity resulted in improved overall classification per-formance compared to using only backscatter-intensity.The RF algorithm appeared to be slightly superior to SVM and ML due to higher overall accuracies,however,at the expense of somewhat longer processing time.The best overall accuracy(OA)for three methodologies were achieved using combination of all tested features were 71.56,72.93,and 72.91%for ML,RF and SVM classifiers,respectively.Compared to OAs of 62.28,66.51,and 63.05%using only backscatter intensity,this indicates strong benefit of SAR interferometry in discriminating different types of sea ice.In contrast to several earlier studies,we were particularly able to successfully discriminate open water and new ice classes.展开更多
Two-dimensional(2D) materials and their heterostructures have attracted a lot of attention due to their unique electronic and optical properties. MoS_(2) as the most typical 2D semiconductors has great application pot...Two-dimensional(2D) materials and their heterostructures have attracted a lot of attention due to their unique electronic and optical properties. MoS_(2) as the most typical 2D semiconductors has great application potential in thin film transistors, photodetector, hydrogen evolution reaction, memory device, etc. However, the performance of MoS_(2) devices is limited by the contact resistance and the improvement of its contact quality is important. In this work, we report the experimental investigation of pressure-enhanced contact quality between monolayer MoS_(2) and graphite by conductive atom force microscope(C-AFM). It was found that at high pressure, the contact quality between graphite and MoS_(2) is significantly improved. This pressure-mediated contact quality improvement between MoS_(2) and graphite comes from the enhanced charge transfer between MoS_(2) and graphite when MoS_(2) is stretched. Our results provide a new way to enhance the contact quality between MoS_(2) and graphite for further applications.展开更多
Transition metal dichalcogenides(TMDs),being valley selectively,are an ideal system hosting excitons.Stacking TMDs together to form heterostructure offers an exciting platform to engineer new optical and electronic pr...Transition metal dichalcogenides(TMDs),being valley selectively,are an ideal system hosting excitons.Stacking TMDs together to form heterostructure offers an exciting platform to engineer new optical and electronic properties in solid-state systems.However,due to the limited accuracy and repetitiveness of sample preparation,the effects of interlayer coupling on the electronic and excitonic properties have not been systematically investigated.In this report,we study the photoluminescence spectra of bilayer-bilayer MoS_(2)/WS_(2) heterostructure with a typeⅡband alignment.We demonstrate that thermal annealing can increase interlayer coupling in the van der Waals heterostructures,and after thermally induced band hybridization such heterostructure behaves more like an artificial new solid,rather than just the combination of two individual TMD components.We also carry out experimental and theoretical studies of the electric controllable direct and indirect infrared interlayer excitons in such system.Our study reveals the impact of interlayer coupling on interlayer excitons and will shed light on the understanding and engineering of layer-controlled spin-valley configuration in twisted van der Waals heterostructures.展开更多
The light-matter interaction in materials is of remarkable interest for various photonic and optoelectronic applications,which is intrinsically determined by the bandgap of the materials involved.To extend the applica...The light-matter interaction in materials is of remarkable interest for various photonic and optoelectronic applications,which is intrinsically determined by the bandgap of the materials involved.To extend the applications beyond the bandgap limit,it is of great significance to study the light-matter interaction below the material bandgap.Here,we report the ultrafast transient absorption of monolayer molybdenum disulfide in its sub-bandgap region from-0.86 pm to 1.4 pm.Even though this spectral range is below the bandgap,we observe a significant absorbance enhancement up to-4.2%in the monolayer molybdenum disulfide(comparable to its absorption within the bandgap region)due to pump-induced absorption by the excited carrier states.The different rise times of the transient absorption at different wavelengths indicate the various contributions of the different carrier states(i.e.,real carrier states in the short-wavelength region of~<1μm,and exciton states in the long wavelength region of~>1μm).Our results elucidate the fundamental understanding regarding the optical properties,excited carrier states,and carrier dynamics in the technologically important near-infrared region,which potentially leads to various photonic and optoelectronic applications(e.g„excited-state-based photodetectors and modulators)of two-dimensional materials and their heterostructures beyond their intrinsic bandgap limitations.展开更多
Indium phosphide(InP)nanowires(NWs)have attracted significant attention due to their exotic properties that are different from the bulk counterparts,and have been widely used for light generation,amplification,detecti...Indium phosphide(InP)nanowires(NWs)have attracted significant attention due to their exotic properties that are different from the bulk counterparts,and have been widely used for light generation,amplification,detection,modulation,and switching,etc.Here,high-quality InP NWs were directly grown on a quartz substrate by the Au-nanoparticle assisted vapor-liquid-solid method.We thoroughly studied their nonlinear optical absorption properties at 1.06μm by the open-aperture Z-scan method.Interestingly,a transition phenomenon from satu-rable absorption(SA)to reverse saturable absorption(RSA)was observed with the increase of the incident laser intensity.In the analysis,we found that the effective nonlinear absorption cofficient(βeff-10^2 cm/MW)under the SA process was 3 orders of magnitude larger than that during the RSA processes.Furthermore,the SA proper-ties of InP NWs were experimentally verified by using them as a saturable absorber for a passively Q-switched Nd:YVO4 solid-state laser at 1.06μm,where the shortest pulse width of 462 ns and largest single pulse energy of 1.32μJ were obtained.Moreover,the ultrafast carrier relaxation dynamics were basically studied,and the intraband and inter-band ultrafast carrier relaxation times of 8.1 and 63.8 ps,respectively,were measured by a degenerate pump-probe method with the probe laser of 800 nm.These results well demonstrate the nonlinear optical absorption properties,which show the excellent light manipulating capabilities of InP NWs and pave a way for their applications in ultrafast nanophotonic devices.展开更多
We propose and demonstrate a passively mode-locked erbium-doped fiber laser(EDFL)based on zinc-oxide/polydimethylsiloxane(ZnO/PDMS)saturable absorber(SA)that evanescently interacts with the light on a tapered fiber.Th...We propose and demonstrate a passively mode-locked erbium-doped fiber laser(EDFL)based on zinc-oxide/polydimethylsiloxane(ZnO/PDMS)saturable absorber(SA)that evanescently interacts with the light on a tapered fiber.The ZnO/PDMS composite is coated on the whole surface of the tapered fiber to guarantee the maximum efficiency of the SA device,with a measured insertion loss of 0.87 dB and a modulation depth of 6.4%.The proposed laser can generate soliton mode-locking operation at a threshold power of 33.07 mW.The generated output pulse yields a repetition rate and pulse width of 9.77 MHz and 1.03 ps,respectively.These results indicate that the proposed ZnO/PDMS-clad tapered fiber could be useful as an efficient,compatible,and low-cost SA device for ultrafast laser applications.展开更多
In 1980,scientist Klaus von Klitzing discovered the quantum Hall effect[1],a groundbreaking achievement that earned him the Nobel Prize in Physics in 1985.This discovery was a significant milestone in condensed matter...In 1980,scientist Klaus von Klitzing discovered the quantum Hall effect[1],a groundbreaking achievement that earned him the Nobel Prize in Physics in 1985.This discovery was a significant milestone in condensed matter physics,representing the first identification of topological quantum states.展开更多
We propose an optomechanical system to quantify the net force on a strand of cleaved silica optical fiber in situ as the laser light is being guided through it.Four strands of the fiber were bonded to both sides of a ...We propose an optomechanical system to quantify the net force on a strand of cleaved silica optical fiber in situ as the laser light is being guided through it.Four strands of the fiber were bonded to both sides of a macroscopic oscillator,whose movements were accurately monitored by a Michelson interferometer.The laser light was propagating with variable optical powers and frequency modulations.Experimentally,we discovered that the driving force for the oscillator consisted of not only the optical force of the light exiting from the cleaved facets but also the tension along the fiber induced by the light guided therewithin.The net driving force was determined only by the optical power,refractive index of the fiber,and the speed of light,which pinpoints its fundamental origin.展开更多
Indium arsenide phosphide(In As P)nanowires(NWs),a member of theⅢ–Ⅴsemiconductor family,have been used in various photonic and optoelectronic applications thanks to their unique electrical and optical properties su...Indium arsenide phosphide(In As P)nanowires(NWs),a member of theⅢ–Ⅴsemiconductor family,have been used in various photonic and optoelectronic applications thanks to their unique electrical and optical properties such as high carrier mobility and adjustable band gap.In this work,we synthesize In As P NWs and further explore their nonlinear optical properties.The ultrafast carrier dynamics and nonlinear optical response are thoroughly studied based on the nondegenerate pump probe and Z-scan experimental measurements.Two different characteristic carrier lifetimes(~2 and~15 ps)from In As P NWs are observed during the excited-carrier relaxation process.Based on the physical model analysis,the relaxation process can be ascribed to the carrier cooling process via carrier-phonon scattering and Auger recombination.In addition,based on the measured excited-carrier lifetime and Pauli-blocking principle,we discover that In As P NWs show strong saturable absorption properties at the wavelengths of 532 and 1064 nm.Last,we demonstrate for the first time a femtosecond(~426 fs)solid-state laser based on an In As P NWs saturable absorber at 1.04μm.We believe that our work provides a better understanding of the In As P NWs optical properties and will further advance their photonic applications in the near-infrared range.展开更多
As the role of missions and experiments carried out in outer space becomes more and more essential in our understanding of many earthly problems,such as resource management,environmental problems,and disaster manageme...As the role of missions and experiments carried out in outer space becomes more and more essential in our understanding of many earthly problems,such as resource management,environmental problems,and disaster management,as well as space science questions,thanks to their lower cost and faster development process CubeSats can benefit humanity and therefore,young scientists and engineers have been motivated to research and develop new CubeSat missions.Not very long after their inception,CubeSats have evolved to become accepted platforms for scientific and commercial applications.The last couple of years showed that they are a feasible tool for conducting scientific experiments,not only in the Earth orbit but also in the interplanetary space.For many countries,a CubeSat mission could prompt the community and young teams around the world to build the national capacity to launch and operate national space missions.This paper presents an overview of the key scientific and engineering gateways opened up to the younger scientific community by the advent and adaptation of new technology into CubeSat missions.The role of cooperation and the opportunities for capacity-building and education are also explored.Thus,the present article also aims to provide useful recommendations to scientists,early-career researchers,engineers,students,and anyone who intends to explore the potential and opportunities offered by CubeSats and CubeSats-based missions.展开更多
The giant bulk photovoltaic effect in tellurene nanomaterials has been harnessed to enable broadband infrared neuromodulation,expanding the potential for safe,non-invasive neural stimulation and highlighting the impor...The giant bulk photovoltaic effect in tellurene nanomaterials has been harnessed to enable broadband infrared neuromodulation,expanding the potential for safe,non-invasive neural stimulation and highlighting the importance of material innovation in advancing infrared photonic applications.展开更多
Graphene is a two-dimensional material showing excellent properties for utilization in transparent electrodes;it has low sheet resistance,high optical transmission and is flexible.Whereas the most common transparent e...Graphene is a two-dimensional material showing excellent properties for utilization in transparent electrodes;it has low sheet resistance,high optical transmission and is flexible.Whereas the most common transparent electrode material,tin-doped indium-oxide(ITO)is brittle,less transparent and expensive,which limit its compatibility in flexible electronics as well as in low-cost devices.Here we review two large-area fabrication methods for graphene based transparent electrodes for industry:liquid exfoliation and low-pressure chemical vapor deposition(CVD).We discuss the basic methodologies behind the technologies with an emphasis on optical and electrical properties of recent results.State-of-the-art methods for liquid exfoliation have as a figure of merit an electrical and optical conductivity ratio of 43.5,slightly over the minimum required for industry of 35,while CVD reaches as high as 419.展开更多
Interests surrounding the development of on-chip nonlinear optical devices have been consistently growing in the past decades due to the tremendous applications,such as quantum photonics,all-optical communications,opt...Interests surrounding the development of on-chip nonlinear optical devices have been consistently growing in the past decades due to the tremendous applications,such as quantum photonics,all-optical communications,optical computing,on-chip metrology,and sensing.Developing efficient on-chip nonlinear optical devices to meet the requirements of those applications brings the need for new directions to improve the existing photonic approaches.Recent research has directed the field of on-chip nonlinear optics toward the hybrid integration of two-dimensional layered materials(such as graphene,transition metal dichalcogenides,and black phosphorous)with various integrated platforms.The combination of well-known photonic chip design platforms(e.g.,silicon,silicon nitride)and different two-dimensional layered materials has opened the road for more versatile and efficient structures and devices,which has the great potential to unlock numerous new possibilities.This review discusses the modeling and characterization of different hybrid photonic integration structures with two-dimensional materials,highlights the current state of the art examples,and presents an outlook for future prospects.展开更多
Light modulation is of paramount importance for photonics and optoelectronics. Here we report all-optical coherent modulation of third-harmonic generation (THG) with chiral light via the symmetry enabled polarization ...Light modulation is of paramount importance for photonics and optoelectronics. Here we report all-optical coherent modulation of third-harmonic generation (THG) with chiral light via the symmetry enabled polarization selectivity. The concept is experimentally validated in monolayer materials (MoS2) with modulation depth approaching ~100%, ultra-fast modulation speed (<~130 fs), and wavelength-independence features. Moreover, the power and polarization of the incident optical beams can be used to tune the output chirality and modulation performance. Major performance of our demonstration reaches the fundamental limits of optical modulation: near-unity modulation depth, instantaneous speed (ultra-fast coherent interaction), compact footprint (atomic thickness), and unlimited operation bandwidth, which hold an ideal optical modulation solution for emerging and future nonlinear optical applications (e.g., interconnection, imaging, computing, and quantum technologies).展开更多
Plasma waves play an important role in many solid-state phenomena and devices.They also become significant in electronic device structures as the operation frequencies of these devices increase.A prominent example is ...Plasma waves play an important role in many solid-state phenomena and devices.They also become significant in electronic device structures as the operation frequencies of these devices increase.A prominent example is field-effect transistors(FETs),that witness increased attention for application as rectifying detectors and mixers of electromagnetic waves at gigahertz and terahertz frequencies,where they exhibit very good sensitivity even high above the cut-off frequency defined by the carrier transit time.Transport theory predicts that the coupling of radiation at THz frequencies into the channel of an antenna-coupled FET leads to the development of a gated plasma wave,collectively involving the charge carriers of both the two-dimensional electron gas and the gate electrode.In this paper,we present the first direct visualization of these waves.Employing graphene FETs containing a buried gate electrode,we utilize near-field THz nanoscopy at room temperature to directly probe the envelope function of the electric field amplitude on the exposed graphene sheet and the neighboring antenna regions.Mapping of the field distribution documents that wave injection is unidirectional from the source side since the oscillating electrical potentials on the gate and drain are equalized by capacitive shunting.The plasma waves,excited at 2 THz,are overdamped,and their decay time lies in the range of 25-70 fs.Despite this short decay time,the decay length is rather long,i.e.,0.3-0.5μm,because of the rather large propagation speed of the plasma waves,which is found to lie in the range of 3.5-7×10^(6)m/s,in good agreement with theory.The propagation speed depends only weakly on the gate voltage swing and is consistent with the theoretically predicted 1/4 power law.展开更多
The position-dependent mode couplings between a semiconductor nanowire(NW)and a planar photonic crystal(PPC)nanocavity are studied.By scanning an NW across a PPC nanocavity along the hexagonal lattice’sΓ– M and M–...The position-dependent mode couplings between a semiconductor nanowire(NW)and a planar photonic crystal(PPC)nanocavity are studied.By scanning an NW across a PPC nanocavity along the hexagonal lattice’sΓ– M and M– K directions,the variations of resonant wavelengths,quality factors,and mode volumes in both fundamental and second-order resonant modes are calculated,implying optimal configurations for strong mode-NW couplings and light-NW interactions.For the fundamental(second-order)resonant mode,scanning an NW along the M– K(Γ– M)direction is preferred,which supports stronger light-NW interactions with larger NW-position tolerances and higher quality factors simultaneously.The simulation results are confirmed experimentally with good agreements.展开更多
Robust signal transfer in the form of electromagnetic waves is of fundamental importance in modern technology,yet its operation is often challenged by unwanted modifications of the channel connecting transmitter and r...Robust signal transfer in the form of electromagnetic waves is of fundamental importance in modern technology,yet its operation is often challenged by unwanted modifications of the channel connecting transmitter and receiver.Parity-time-(PT-)symmetric systems,combining active and passive elements in a balanced form,provide an interesting route in this context.Here,we demonstrate a PT-symmetric microwave system operating in the extreme case in which the channel is shorted through a small reactance,which acts as a nearly impenetrable obstacle,and it is therefore expected to induce large reflections and poor transmission.After placing a gain element behind the obstacle,and a balanced lossy element in front of it,we observe full restoration of information and overall transparency to an external observer,despite the presence of the obstacle.Our theory,simulations,and experiments unambiguously demonstrate stable and robust wave tunneling and information transfer supported by PT symmetry,opening opportunities for efficient communication through channels with dynamic changes,active filtering,and active metamaterial technology.展开更多
The MODIS LAI/FPAR products have been widely used in various fields since their first public release in 2000.This review intends to summarize the history,development trends,scientific collaborations,disciplines involv...The MODIS LAI/FPAR products have been widely used in various fields since their first public release in 2000.This review intends to summarize the history,development trends,scientific collaborations,disciplines involved,and research hotspots of these products.Its aim is to intrigue researchers and stimulate new research direction.Based on literature data from the Web of Science(WOS)and associated funding information,we conducted a bibliometric visualization review of the MODIS LAI/FPAR products from 1995 to 2020 using bibliometric and social network analysis(SNA)methods.We drew the following conclusions:(1)research based on the MODIS LAI/FPAR shows an upward trend with a multiyear average growth rate of 24.9%in the number of publications.(2)Researchers from China and the USA are the backbone of this research area,among which the Chinese Academy of Sciences(CAS)is the core research institution.(3)Research based on the MODIS LAI/FPAR covers a wide range of disciplines but mainly focus on environmental science and ecology.(4)Ecology,crop production estimation,algorithm improvement,and validation are the hotspots of these studies.(5)Broadening the research field,improving the algorithms,and overcoming existing difficulties in heterogeneous surface,scale effects,and complex terrains will be the trend of future research.Our work provides a clear view of the development of the MODIS LAI/FPAR products and valuable information for scholars to broaden their research fields.展开更多
Silicon-based field effect transistors(FETs)are the building blocks of modern electronics,serving as the cornerstone.However,current silicon technology is approaching its performance-downscaling limits[1].This challen...Silicon-based field effect transistors(FETs)are the building blocks of modern electronics,serving as the cornerstone.However,current silicon technology is approaching its performance-downscaling limits[1].This challenge primarily stems from the substantial decline in electron mobility as silicon-based semiconductor thickness decreases,coupled with the pronounced emergence of short-channel effects upon FET miniaturization[1,2].展开更多
Interlayer twist evokes revolutionary changes to the optical and electronic properties of twisted bilayer graphene(TBG)for electronics,photonics and optoelectronics.Although the ground state responses in TBG have been...Interlayer twist evokes revolutionary changes to the optical and electronic properties of twisted bilayer graphene(TBG)for electronics,photonics and optoelectronics.Although the ground state responses in TBG have been vastly and clearly studied,the dynamic process of its photoexcited carrier states mainly remains elusive.Here,we unveil the photoexcited hot carrier dynamics in TBG by time-resolved ultrafast photoluminescence(PL)autocorrelation spectroscopy.We demonstrate the unconventional ultrafast PL emission between the van Hove singularities(VHSs)with a~4 times prolonged relaxation lifetime.This intriguing photoexcited carrier behavior is ascribed to the abnormal hot carrier thermalization brought by bottleneck effects at VHSs and interlayer charge distribution process.Our study on hot carrier dynamics in TBG offers new insights into the excited states and correlated physics of graphene twistronics systems.展开更多
基金This research was supported by Academy of Finland under Grant no.296628.
文摘In this study,we assess the potential of X-band Interferometric Synthetic Aperture Radar imagery for automated classification of sea ice over the Baltic Sea.A bistatic SAR scene acquired by the TanDEM-X mission over the Bothnian Bay in March of 2012 was used in the analysis.Backscatter intensity,interferometric coherence magnitude,and interferometric phase have been used as informative features in several classification experiments.Various combinations of classification features were evaluated using Maximum likelihood(ML),Random Forests(RF)and Support Vector Machine(SVM)classifiers to achieve the best possible discrimination between open water and several sea ice types(undeformed ice,ridged ice,moderately deformed ice,brash ice,thick level ice,and new ice).Adding interferometric phase and coherence-magnitude to backscatter-intensity resulted in improved overall classification per-formance compared to using only backscatter-intensity.The RF algorithm appeared to be slightly superior to SVM and ML due to higher overall accuracies,however,at the expense of somewhat longer processing time.The best overall accuracy(OA)for three methodologies were achieved using combination of all tested features were 71.56,72.93,and 72.91%for ML,RF and SVM classifiers,respectively.Compared to OAs of 62.28,66.51,and 63.05%using only backscatter intensity,this indicates strong benefit of SAR interferometry in discriminating different types of sea ice.In contrast to several earlier studies,we were particularly able to successfully discriminate open water and new ice classes.
基金Project supported by the National Key R&D Program,China(Grant No.2016YFA0300904)the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(Grant No.QYZDB-SSW-SLH004)+1 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant Nos.XDPB06 and XDB07010100)the National Natural Science Foundation of China(Grant Nos.61734001 and 51572289)
文摘Two-dimensional(2D) materials and their heterostructures have attracted a lot of attention due to their unique electronic and optical properties. MoS_(2) as the most typical 2D semiconductors has great application potential in thin film transistors, photodetector, hydrogen evolution reaction, memory device, etc. However, the performance of MoS_(2) devices is limited by the contact resistance and the improvement of its contact quality is important. In this work, we report the experimental investigation of pressure-enhanced contact quality between monolayer MoS_(2) and graphite by conductive atom force microscope(C-AFM). It was found that at high pressure, the contact quality between graphite and MoS_(2) is significantly improved. This pressure-mediated contact quality improvement between MoS_(2) and graphite comes from the enhanced charge transfer between MoS_(2) and graphite when MoS_(2) is stretched. Our results provide a new way to enhance the contact quality between MoS_(2) and graphite for further applications.
基金the National Key Research and Development Program of China(Grant No.2020YFA0309604)the National Natural Science Foundation of China(Grant Nos.11834017,61888102,and 12074413)+2 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDB30000000 and XDB33000000)the Key-Area Research and Development Program of Guangdong Province,China(Grant No.2020B0101340001)the Research Program of Beijing Academy of Quantum Information Sciences(Grant No.Y18G11).
文摘Transition metal dichalcogenides(TMDs),being valley selectively,are an ideal system hosting excitons.Stacking TMDs together to form heterostructure offers an exciting platform to engineer new optical and electronic properties in solid-state systems.However,due to the limited accuracy and repetitiveness of sample preparation,the effects of interlayer coupling on the electronic and excitonic properties have not been systematically investigated.In this report,we study the photoluminescence spectra of bilayer-bilayer MoS_(2)/WS_(2) heterostructure with a typeⅡband alignment.We demonstrate that thermal annealing can increase interlayer coupling in the van der Waals heterostructures,and after thermally induced band hybridization such heterostructure behaves more like an artificial new solid,rather than just the combination of two individual TMD components.We also carry out experimental and theoretical studies of the electric controllable direct and indirect infrared interlayer excitons in such system.Our study reveals the impact of interlayer coupling on interlayer excitons and will shed light on the understanding and engineering of layer-controlled spin-valley configuration in twisted van der Waals heterostructures.
基金support from Academy of Finland(Grant Nos.314810,333982,336144 and 336818)Academy of Finland Flagship Program(Grant No 320167,PREIN)+2 种基金the European Union's Horizon 2020 research and innovation program(Grant No.820423,S2QUIP)the EU H2020-MSCA-RISE-872049(IPN-Bio)ERC(Grant No 834742).
文摘The light-matter interaction in materials is of remarkable interest for various photonic and optoelectronic applications,which is intrinsically determined by the bandgap of the materials involved.To extend the applications beyond the bandgap limit,it is of great significance to study the light-matter interaction below the material bandgap.Here,we report the ultrafast transient absorption of monolayer molybdenum disulfide in its sub-bandgap region from-0.86 pm to 1.4 pm.Even though this spectral range is below the bandgap,we observe a significant absorbance enhancement up to-4.2%in the monolayer molybdenum disulfide(comparable to its absorption within the bandgap region)due to pump-induced absorption by the excited carrier states.The different rise times of the transient absorption at different wavelengths indicate the various contributions of the different carrier states(i.e.,real carrier states in the short-wavelength region of~<1μm,and exciton states in the long wavelength region of~>1μm).Our results elucidate the fundamental understanding regarding the optical properties,excited carrier states,and carrier dynamics in the technologically important near-infrared region,which potentially leads to various photonic and optoelectronic applications(e.g„excited-state-based photodetectors and modulators)of two-dimensional materials and their heterostructures beyond their intrinsic bandgap limitations.
基金National Natural Science Foundation of China(61575110,61675116,61975095)Department of Science and Technology of Shandong Province(2017WLJH48)+3 种基金Shandong University(2020QNQT)Academy of Finland Photonics Flagship PREIN(320167)Walter AhLströmin SäätiöNokia.
文摘Indium phosphide(InP)nanowires(NWs)have attracted significant attention due to their exotic properties that are different from the bulk counterparts,and have been widely used for light generation,amplification,detection,modulation,and switching,etc.Here,high-quality InP NWs were directly grown on a quartz substrate by the Au-nanoparticle assisted vapor-liquid-solid method.We thoroughly studied their nonlinear optical absorption properties at 1.06μm by the open-aperture Z-scan method.Interestingly,a transition phenomenon from satu-rable absorption(SA)to reverse saturable absorption(RSA)was observed with the increase of the incident laser intensity.In the analysis,we found that the effective nonlinear absorption cofficient(βeff-10^2 cm/MW)under the SA process was 3 orders of magnitude larger than that during the RSA processes.Furthermore,the SA proper-ties of InP NWs were experimentally verified by using them as a saturable absorber for a passively Q-switched Nd:YVO4 solid-state laser at 1.06μm,where the shortest pulse width of 462 ns and largest single pulse energy of 1.32μJ were obtained.Moreover,the ultrafast carrier relaxation dynamics were basically studied,and the intraband and inter-band ultrafast carrier relaxation times of 8.1 and 63.8 ps,respectively,were measured by a degenerate pump-probe method with the probe laser of 800 nm.These results well demonstrate the nonlinear optical absorption properties,which show the excellent light manipulating capabilities of InP NWs and pave a way for their applications in ultrafast nanophotonic devices.
基金the Ministry of Higher Education of Malaysia(MOHE)(Grant No.FRGS/1/2019/STG02/UPM/02/4).
文摘We propose and demonstrate a passively mode-locked erbium-doped fiber laser(EDFL)based on zinc-oxide/polydimethylsiloxane(ZnO/PDMS)saturable absorber(SA)that evanescently interacts with the light on a tapered fiber.The ZnO/PDMS composite is coated on the whole surface of the tapered fiber to guarantee the maximum efficiency of the SA device,with a measured insertion loss of 0.87 dB and a modulation depth of 6.4%.The proposed laser can generate soliton mode-locking operation at a threshold power of 33.07 mW.The generated output pulse yields a repetition rate and pulse width of 9.77 MHz and 1.03 ps,respectively.These results indicate that the proposed ZnO/PDMS-clad tapered fiber could be useful as an efficient,compatible,and low-cost SA device for ultrafast laser applications.
文摘In 1980,scientist Klaus von Klitzing discovered the quantum Hall effect[1],a groundbreaking achievement that earned him the Nobel Prize in Physics in 1985.This discovery was a significant milestone in condensed matter physics,representing the first identification of topological quantum states.
基金Ministry of Science and ICT,South Korea(2019R1A2C2011293)Research Executive Agency(846218).
文摘We propose an optomechanical system to quantify the net force on a strand of cleaved silica optical fiber in situ as the laser light is being guided through it.Four strands of the fiber were bonded to both sides of a macroscopic oscillator,whose movements were accurately monitored by a Michelson interferometer.The laser light was propagating with variable optical powers and frequency modulations.Experimentally,we discovered that the driving force for the oscillator consisted of not only the optical force of the light exiting from the cleaved facets but also the tension along the fiber induced by the light guided therewithin.The net driving force was determined only by the optical power,refractive index of the fiber,and the speed of light,which pinpoints its fundamental origin.
基金National Natural Science Foundation of China(61975095,61975097)Qilu Young Scholar of Shandong University,Youth Cross Innovation Group of Shandong University(2020QNQT)+7 种基金Self-made Equipment Cultivation Project of Shandong University(ZY202002)European Union(H2020-MSCA-RISE-872049(IPN-Bio))Aalto University Doctoral SchoolWalter Ahlstr?min S??ti?Elektroniikkainsin??rien S??ti?S?hk?insin??riliiton S??ti?Nokia FoundationAcademy of Finland(320167)。
文摘Indium arsenide phosphide(In As P)nanowires(NWs),a member of theⅢ–Ⅴsemiconductor family,have been used in various photonic and optoelectronic applications thanks to their unique electrical and optical properties such as high carrier mobility and adjustable band gap.In this work,we synthesize In As P NWs and further explore their nonlinear optical properties.The ultrafast carrier dynamics and nonlinear optical response are thoroughly studied based on the nondegenerate pump probe and Z-scan experimental measurements.Two different characteristic carrier lifetimes(~2 and~15 ps)from In As P NWs are observed during the excited-carrier relaxation process.Based on the physical model analysis,the relaxation process can be ascribed to the carrier cooling process via carrier-phonon scattering and Auger recombination.In addition,based on the measured excited-carrier lifetime and Pauli-blocking principle,we discover that In As P NWs show strong saturable absorption properties at the wavelengths of 532 and 1064 nm.Last,we demonstrate for the first time a femtosecond(~426 fs)solid-state laser based on an In As P NWs saturable absorber at 1.04μm.We believe that our work provides a better understanding of the In As P NWs optical properties and will further advance their photonic applications in the near-infrared range.
文摘As the role of missions and experiments carried out in outer space becomes more and more essential in our understanding of many earthly problems,such as resource management,environmental problems,and disaster management,as well as space science questions,thanks to their lower cost and faster development process CubeSats can benefit humanity and therefore,young scientists and engineers have been motivated to research and develop new CubeSat missions.Not very long after their inception,CubeSats have evolved to become accepted platforms for scientific and commercial applications.The last couple of years showed that they are a feasible tool for conducting scientific experiments,not only in the Earth orbit but also in the interplanetary space.For many countries,a CubeSat mission could prompt the community and young teams around the world to build the national capacity to launch and operate national space missions.This paper presents an overview of the key scientific and engineering gateways opened up to the younger scientific community by the advent and adaptation of new technology into CubeSat missions.The role of cooperation and the opportunities for capacity-building and education are also explored.Thus,the present article also aims to provide useful recommendations to scientists,early-career researchers,engineers,students,and anyone who intends to explore the potential and opportunities offered by CubeSats and CubeSats-based missions.
文摘The giant bulk photovoltaic effect in tellurene nanomaterials has been harnessed to enable broadband infrared neuromodulation,expanding the potential for safe,non-invasive neural stimulation and highlighting the importance of material innovation in advancing infrared photonic applications.
基金funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement GrapheneCore2 number 785219,and GrapheneCore3 number 881603the financial support from Academy of Finland(projects 298297 and 320167-PREIN Flagship).
文摘Graphene is a two-dimensional material showing excellent properties for utilization in transparent electrodes;it has low sheet resistance,high optical transmission and is flexible.Whereas the most common transparent electrode material,tin-doped indium-oxide(ITO)is brittle,less transparent and expensive,which limit its compatibility in flexible electronics as well as in low-cost devices.Here we review two large-area fabrication methods for graphene based transparent electrodes for industry:liquid exfoliation and low-pressure chemical vapor deposition(CVD).We discuss the basic methodologies behind the technologies with an emphasis on optical and electrical properties of recent results.State-of-the-art methods for liquid exfoliation have as a figure of merit an electrical and optical conductivity ratio of 43.5,slightly over the minimum required for industry of 35,while CVD reaches as high as 419.
基金supported by Paris Saclay University within the Centre for Nanoscience and Nanotechnology(C2N)in France and Aalto University in Finland.ZS thanks fundings from the Academy of Finland(314810,333982,336144,336818,352780,353364)the Academy of Finland Flagship Programme(320167,PREIN)the EU H2020-MSCA-RISE-872049(IPN-Bio),and ERC(834742).
文摘Interests surrounding the development of on-chip nonlinear optical devices have been consistently growing in the past decades due to the tremendous applications,such as quantum photonics,all-optical communications,optical computing,on-chip metrology,and sensing.Developing efficient on-chip nonlinear optical devices to meet the requirements of those applications brings the need for new directions to improve the existing photonic approaches.Recent research has directed the field of on-chip nonlinear optics toward the hybrid integration of two-dimensional layered materials(such as graphene,transition metal dichalcogenides,and black phosphorous)with various integrated platforms.The combination of well-known photonic chip design platforms(e.g.,silicon,silicon nitride)and different two-dimensional layered materials has opened the road for more versatile and efficient structures and devices,which has the great potential to unlock numerous new possibilities.This review discusses the modeling and characterization of different hybrid photonic integration structures with two-dimensional materials,highlights the current state of the art examples,and presents an outlook for future prospects.
基金Aalto Centre for Quantum Engineering,Academy of Finland(grants:314810,333982,336144,and 336818)Academy of Finland Flagship Programme(320167,PREIN)+3 种基金the European Union’s Horizon 2020 research and innovation program(Grant agreement Nos.820423,S2QUIP,965124,FEMTOCHIP)the EU H2020-MSCA-RISE-872049(IPN-Bio)ERC advanced grant(834742)HORIZON-MSCA-2021-PF-01-01(680225).
文摘Light modulation is of paramount importance for photonics and optoelectronics. Here we report all-optical coherent modulation of third-harmonic generation (THG) with chiral light via the symmetry enabled polarization selectivity. The concept is experimentally validated in monolayer materials (MoS2) with modulation depth approaching ~100%, ultra-fast modulation speed (<~130 fs), and wavelength-independence features. Moreover, the power and polarization of the incident optical beams can be used to tune the output chirality and modulation performance. Major performance of our demonstration reaches the fundamental limits of optical modulation: near-unity modulation depth, instantaneous speed (ultra-fast coherent interaction), compact footprint (atomic thickness), and unlimited operation bandwidth, which hold an ideal optical modulation solution for emerging and future nonlinear optical applications (e.g., interconnection, imaging, computing, and quantum technologies).
基金funding from the Adolf Messer Stiftungthe Friedrich-Ebert Stiftung+5 种基金the Rosa Luxemburg Stiftungthe EU-funded action H2020-MSCA-ITN-2015-ETN CELTAfunded by the Deutsche Forschungsgemeinschaft(DFG project RO 770/40)support via the BMBF projects 05K16ODA,05K16ODC,05K19ODA,and 05K19ODBfunding from the Swedish Research Council(grant no.2017.-04504)funding from the Academy of Finland(grant nos.325810,312297,320167,and 314810).
文摘Plasma waves play an important role in many solid-state phenomena and devices.They also become significant in electronic device structures as the operation frequencies of these devices increase.A prominent example is field-effect transistors(FETs),that witness increased attention for application as rectifying detectors and mixers of electromagnetic waves at gigahertz and terahertz frequencies,where they exhibit very good sensitivity even high above the cut-off frequency defined by the carrier transit time.Transport theory predicts that the coupling of radiation at THz frequencies into the channel of an antenna-coupled FET leads to the development of a gated plasma wave,collectively involving the charge carriers of both the two-dimensional electron gas and the gate electrode.In this paper,we present the first direct visualization of these waves.Employing graphene FETs containing a buried gate electrode,we utilize near-field THz nanoscopy at room temperature to directly probe the envelope function of the electric field amplitude on the exposed graphene sheet and the neighboring antenna regions.Mapping of the field distribution documents that wave injection is unidirectional from the source side since the oscillating electrical potentials on the gate and drain are equalized by capacitive shunting.The plasma waves,excited at 2 THz,are overdamped,and their decay time lies in the range of 25-70 fs.Despite this short decay time,the decay length is rather long,i.e.,0.3-0.5μm,because of the rather large propagation speed of the plasma waves,which is found to lie in the range of 3.5-7×10^(6)m/s,in good agreement with theory.The propagation speed depends only weakly on the gate voltage swing and is consistent with the theoretically predicted 1/4 power law.
基金supported by the Key Research and Development Program(No.2017YFA0303800)the NSFC(Nos.61522507,61775183,and 11634010)+4 种基金the Key Research and Development Program in Shaanxi Province of China(No.2017KJXX-12)the Doctorate Foundation of Northwestern Polytechnical University(No.CX201924)the Academy of Finland(Nos.276376,284548,295777,304666,312297,312551,and 314810)TEKES(OPEC),he European Union Seventh Framework Program(No.631610)Aalto University Doctoral School,Walter Ahlstrom Foundation,Nokia Foundation
文摘The position-dependent mode couplings between a semiconductor nanowire(NW)and a planar photonic crystal(PPC)nanocavity are studied.By scanning an NW across a PPC nanocavity along the hexagonal lattice’sΓ– M and M– K directions,the variations of resonant wavelengths,quality factors,and mode volumes in both fundamental and second-order resonant modes are calculated,implying optimal configurations for strong mode-NW couplings and light-NW interactions.For the fundamental(second-order)resonant mode,scanning an NW along the M– K(Γ– M)direction is preferred,which supports stronger light-NW interactions with larger NW-position tolerances and higher quality factors simultaneously.The simulation results are confirmed experimentally with good agreements.
基金This work was supported by the Office of Naval Research,the National Science Foundationthe Air Force Office of Scientific Research.
文摘Robust signal transfer in the form of electromagnetic waves is of fundamental importance in modern technology,yet its operation is often challenged by unwanted modifications of the channel connecting transmitter and receiver.Parity-time-(PT-)symmetric systems,combining active and passive elements in a balanced form,provide an interesting route in this context.Here,we demonstrate a PT-symmetric microwave system operating in the extreme case in which the channel is shorted through a small reactance,which acts as a nearly impenetrable obstacle,and it is therefore expected to induce large reflections and poor transmission.After placing a gain element behind the obstacle,and a balanced lossy element in front of it,we observe full restoration of information and overall transparency to an external observer,despite the presence of the obstacle.Our theory,simulations,and experiments unambiguously demonstrate stable and robust wave tunneling and information transfer supported by PT symmetry,opening opportunities for efficient communication through channels with dynamic changes,active filtering,and active metamaterial technology.
基金supported by the National Natural Science Foundation of China[grant number 41901298]the Open Fund of State Key Laboratory of Remote Sensing Science[grant number OFSLRSS201924]+1 种基金the Open Research Fund of Key Laboratory of Digital Earth Science,Institute of Remote Sensing and Digital Earth,Chinese Academy of Sciences[grant number 2018LDE002]the Fundamental Research Funds for the Central Universities[grant number 2652018031].
文摘The MODIS LAI/FPAR products have been widely used in various fields since their first public release in 2000.This review intends to summarize the history,development trends,scientific collaborations,disciplines involved,and research hotspots of these products.Its aim is to intrigue researchers and stimulate new research direction.Based on literature data from the Web of Science(WOS)and associated funding information,we conducted a bibliometric visualization review of the MODIS LAI/FPAR products from 1995 to 2020 using bibliometric and social network analysis(SNA)methods.We drew the following conclusions:(1)research based on the MODIS LAI/FPAR shows an upward trend with a multiyear average growth rate of 24.9%in the number of publications.(2)Researchers from China and the USA are the backbone of this research area,among which the Chinese Academy of Sciences(CAS)is the core research institution.(3)Research based on the MODIS LAI/FPAR covers a wide range of disciplines but mainly focus on environmental science and ecology.(4)Ecology,crop production estimation,algorithm improvement,and validation are the hotspots of these studies.(5)Broadening the research field,improving the algorithms,and overcoming existing difficulties in heterogeneous surface,scale effects,and complex terrains will be the trend of future research.Our work provides a clear view of the development of the MODIS LAI/FPAR products and valuable information for scholars to broaden their research fields.
文摘Silicon-based field effect transistors(FETs)are the building blocks of modern electronics,serving as the cornerstone.However,current silicon technology is approaching its performance-downscaling limits[1].This challenge primarily stems from the substantial decline in electron mobility as silicon-based semiconductor thickness decreases,coupled with the pronounced emergence of short-channel effects upon FET miniaturization[1,2].
基金supported by the National Key R&D Program of China(2021YFA1400201,2022YFA1403504,2021YFB32003032021YFA1400502)+4 种基金the National Natural Science Foundation of China(T2188101,52025023,51991342,52021006,92163206,11888101,and 12374167)Guangdong Major Project of Basic and Applied Basic Research(2021B0301030002)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB33000000)the Pearl River Talent Recruitment Program of Guangdong Province(2019ZT08C321)the New Cornerstone Science Foundation through the XPLORER PRIZE。
文摘Interlayer twist evokes revolutionary changes to the optical and electronic properties of twisted bilayer graphene(TBG)for electronics,photonics and optoelectronics.Although the ground state responses in TBG have been vastly and clearly studied,the dynamic process of its photoexcited carrier states mainly remains elusive.Here,we unveil the photoexcited hot carrier dynamics in TBG by time-resolved ultrafast photoluminescence(PL)autocorrelation spectroscopy.We demonstrate the unconventional ultrafast PL emission between the van Hove singularities(VHSs)with a~4 times prolonged relaxation lifetime.This intriguing photoexcited carrier behavior is ascribed to the abnormal hot carrier thermalization brought by bottleneck effects at VHSs and interlayer charge distribution process.Our study on hot carrier dynamics in TBG offers new insights into the excited states and correlated physics of graphene twistronics systems.
