Nonlinear frequency conversion is one of the most fundamental processes in nonlinear optics.It has a wide range of applications in our daily lives,including novel light sources,sensing,and information processing.It is...Nonlinear frequency conversion is one of the most fundamental processes in nonlinear optics.It has a wide range of applications in our daily lives,including novel light sources,sensing,and information processing.It is usually assumed that nonlinear frequency conversion requires large crystals that gradually accumulate a strong effect.However,the large size of nonlinear crystals is not compatible with the miniaturisation of modern photonic and optoelectronic systems.Therefore,shrinking the nonlinear structures down to the nanoscale,while keeping favourable conversion efficiencies,is of great importance for future photonics applications.In the last decade,researchers have studied the strategies for enhancing the nonlinear efficiencies at the nanoscale,e.g.by employing different nonlinear materials,resonant couplings and hybridization techniques.In this paper,we provide a compact review of the nanomaterials-based efforts,ranging from metal to dielectric and semiconductor nanostructures,including their relevant nanofabrication techniques.展开更多
Zinc oxide nanoparticles with different sizes and shapes have been synthesized in polyol using a bottom-up approach. We have studied the scale-up of the process to massively produce high quality nanoparticles of contr...Zinc oxide nanoparticles with different sizes and shapes have been synthesized in polyol using a bottom-up approach. We have studied the scale-up of the process to massively produce high quality nanoparticles of controlled size and shape. The scale-up strategy required the effective mixing of reagents using either axial or radial mixing configurations and was experimentally validated by comparing structural properties of particles obtained in a small and a large size reactor. In addition, the flow patterns in these reactors have been calculated using three-dimensional turbulent computational fluid dynamics (CFD) simulations. Our results indicate a strong connection between the flow patterns, as obtained by CFD simulations, and the size and shape of the particles. Actually, our pilot scale reactor allowed producing sample aliquots of ~50 grams with nanoparticle sizes ranging from 8 nm to 600 nm and aspect ratio varying from 1 (nanospheres) to 20 (nanorods). After their synthesis, these two nanoparticle classes have been tested as building blocks in D149-dye-sensitized solar cell (DSSC). The measured power conversion efficiency (PCE) was 4.66% for nanorods shaped particles and 4.21% for nanospheres. These values were significantly higher than the 3.90% PCE obtained with commercial Degussa VP20 ZnO nanoparticles.展开更多
The measurement of the magnetic anisotropy of[Fe{(3,5-(CH_(3))_(2)Pz)_(3)BH}_(2)],where Pz=pyrazole,in its high spin state(S=2)by X-ray Magnetic Circular Dichroism(XMCD)spectroscopy when assembled as an organized mono...The measurement of the magnetic anisotropy of[Fe{(3,5-(CH_(3))_(2)Pz)_(3)BH}_(2)],where Pz=pyrazole,in its high spin state(S=2)by X-ray Magnetic Circular Dichroism(XMCD)spectroscopy when assembled as an organized monolayer on Cu(111)shows the presence of a hard axis of magnetization(positive axial zero-field splitting-ZFS-parameter D).Combining magnetization and multifrequency electron paramagnetic resonance spectroscopy on a reference compound,[Fe{(3-(Ph)Pz)_(3)BH}_(2)],of the same family and ab initio wave function based theoretical calculations,we demonstrate that the magnetic anisotropy of the assembled molecules is not affected when they are present at the substrate/vacuum interface.Comparing our results with those of a reported complex having an almost identical FeN_(6)coordination sphere but an easy axis of magnetization(corresponding to a negative D value),we show that the nature of the magnetic anisotropy(easy/hard axis)is governed by the torsion angle(Ψ)defined by the relative orientation of the pyrazole five-membered rings to the pseudo three-fold axis of the molecules.The rigidity of the(Pz)_(3)BH tridentate ligands,where the three pyrazole moieties are held by the BH group,allows only very slight changes in the torsion angle even when the molecules are in a dissymmetric environment such as an interface.This is the origin of the robust magnetic anisotropy of this family of compounds.展开更多
Optical metasurfaces allow complex light manipulation within subwavelength thicknesses and are thus rapidly emerging as a key enabling technology for nanophotonics applications.The control over light polarization alre...Optical metasurfaces allow complex light manipulation within subwavelength thicknesses and are thus rapidly emerging as a key enabling technology for nanophotonics applications.The control over light polarization already provided a route towards ultracompact metasurface-based polarimetry devices.If translated to the nonlinear optical regime it may become a transformative tool for nonlinear imaging,optical holography,and sensing.Here,we report ultrafast all-optical polarization modulation of upconverted light by all-dielectric metasurfaces via nonlinear interferometry.By controlling the relative phase between a pump beam atωand its frequency-doubled replica at 2ω,we can set the phase relation between two frequency-degenerate upconversion processes at 3ω–sum-frequency generation and third-harmonic generation–stemming from an AlGaAs metasurface.By leveraging the opposite parity of the two nonlinear processes and adjusting their relative intensities,we achieve a modulation of the polarization state of the upconverted light between linear and circular states with a circular polarization degree of up to 83%.Remarkably,circularly polarized light of opposite handedness is symmetrically mapped in the Fourier space,at coincidence with the first diffraction orders of the metasurface.Furthermore,the handedness can be completely reversed within the same diffraction order by applying a phase delay ofπ.Our work adds an additional modulation layer beyond intensity to all-optical routing with precise phase control:polarization.The capability to encode and modulate simultaneously different polarization states in the k-space holds potential for chiral sensing and advanced imaging techniques.展开更多
Infrared imaging is a crucial technique in a multitude of applications,including night vision,autonomous vehicle navigation,optical tomography,and food quality control.Conventional infrared imaging technologies,howeve...Infrared imaging is a crucial technique in a multitude of applications,including night vision,autonomous vehicle navigation,optical tomography,and food quality control.Conventional infrared imaging technologies,however,require the use of materials such as narrow bandgap semiconductors,which are sensitive to thermal noise and often require cryogenic cooling.We demonstrate a compact all-optical alternative to perform infrared imaging in a metasurface composed of GaAs semiconductor nanoantennas,using a nonlinear wave-mixing process.We experimentally show the upconversion of short-wave infrared wavelengths via the coherent parametric process of sum-frequency generation.In this process,an infrared image of a target is mixed inside the metasurface with a strong pump beam,translating the image from the infrared to the visible in a nanoscale ultrathin imaging device.Our results open up new opportunities for the development of compact infrared imaging devices with applications in infrared vision and life sciences.展开更多
We demonstrate a chip-integrated semiconductor source that combines polarization and frequency entanglement,allowing the generation of entangled biphoton states in a hybrid degree of freedom without post-manipulation....We demonstrate a chip-integrated semiconductor source that combines polarization and frequency entanglement,allowing the generation of entangled biphoton states in a hybrid degree of freedom without post-manipulation.Our Al Ga As device is based on type-Ⅱ spontaneous parametric downconversion in a counterpropagating phasematching scheme in which the modal birefringence lifts the degeneracy between the two possible nonlinear interactions. This allows the direct generation of polarization–frequency entangled photons at room temperature and telecom wavelength, and in two distinct spatial modes, offering enhanced flexibility for quantum information protocols. The state entanglement is quantified by a combined measurement of the joint spectrum and Hong–Ou–Mandel interference(raw visibility 70.1% ± 1.1%) of the biphotons, allowing to reconstruct a restricted density matrix in the hybrid polarization–frequency space.展开更多
Double perovskite oxides,with generalized formula A_(2)BB'O_(6),attract wide interest due to their multiferroic and charge transfer properties.They offer a wide range of potential applications such as spintronics ...Double perovskite oxides,with generalized formula A_(2)BB'O_(6),attract wide interest due to their multiferroic and charge transfer properties.They offer a wide range of potential applications such as spintronics and electrically tunable devices.However,great practical limitations are encountered,since a spontaneous order of the B-site cations is notoriously hard to achieve.In this joint experimental-theoretical work,we focused on the characterization of double perovskites La2TiFeO6 and La_(2)VCuO_(6) films grown by pulsed laser deposition and interpretation of the observed B-site disorder and partial charge transfer between the B-site ions.A random structure sampling method was used to show that several phases compete due to their corresponding configurational entropy.In order to capture a representative picture of the most relevant competing microstates in realistic experimental conditions,this search included the potential formation of non-stoichiometric phases as well,which could also be directly related to the observed partial charge transfer.We optimized the information encapsulated in the potential energy landscape,captured via structure sampling,by evaluating both enthalpic and entropic terms.These terms were employed as a metric for the competition of different phases.This approach,applied herein specifically to La_(2)TiFeO_(6),highlights the presence of highly entropic phases above the ground state which can explain the disorder observed frequently in the broader class of double perovskite oxides.展开更多
Switching of light polarization on the sub-picosecond timescale is a crucial functionality for applications in a variety of contexts,including telecommunications,biology and chemistry.The ability to control polarizati...Switching of light polarization on the sub-picosecond timescale is a crucial functionality for applications in a variety of contexts,including telecommunications,biology and chemistry.The ability to control polarization at ultrafast speed would pave the way for the development of unprecedented free-space optical links and of novel techniques for probing dynamical processes in complex systems,as chiral molecules.Such high switching speeds can only be reached with an all-optical paradigm,i.e.,engineering active platforms capable of controlling light polarization via ultrashort laser pulses.Here we demonstrate giant modulation of dichroism and birefringence in an all-dielectric metasurface,achieved at low fluences of the optical control beam.This performance,which leverages the many degrees of freedom offered by all-dielectric active metasurfaces,is obtained by combining a high-quality factor nonlocal resonance with the giant third-order optical nonlinearity dictated by photogenerated hot carriers at the semiconductor band edge.展开更多
文摘Nonlinear frequency conversion is one of the most fundamental processes in nonlinear optics.It has a wide range of applications in our daily lives,including novel light sources,sensing,and information processing.It is usually assumed that nonlinear frequency conversion requires large crystals that gradually accumulate a strong effect.However,the large size of nonlinear crystals is not compatible with the miniaturisation of modern photonic and optoelectronic systems.Therefore,shrinking the nonlinear structures down to the nanoscale,while keeping favourable conversion efficiencies,is of great importance for future photonics applications.In the last decade,researchers have studied the strategies for enhancing the nonlinear efficiencies at the nanoscale,e.g.by employing different nonlinear materials,resonant couplings and hybridization techniques.In this paper,we provide a compact review of the nanomaterials-based efforts,ranging from metal to dielectric and semiconductor nanostructures,including their relevant nanofabrication techniques.
文摘Zinc oxide nanoparticles with different sizes and shapes have been synthesized in polyol using a bottom-up approach. We have studied the scale-up of the process to massively produce high quality nanoparticles of controlled size and shape. The scale-up strategy required the effective mixing of reagents using either axial or radial mixing configurations and was experimentally validated by comparing structural properties of particles obtained in a small and a large size reactor. In addition, the flow patterns in these reactors have been calculated using three-dimensional turbulent computational fluid dynamics (CFD) simulations. Our results indicate a strong connection between the flow patterns, as obtained by CFD simulations, and the size and shape of the particles. Actually, our pilot scale reactor allowed producing sample aliquots of ~50 grams with nanoparticle sizes ranging from 8 nm to 600 nm and aspect ratio varying from 1 (nanospheres) to 20 (nanorods). After their synthesis, these two nanoparticle classes have been tested as building blocks in D149-dye-sensitized solar cell (DSSC). The measured power conversion efficiency (PCE) was 4.66% for nanorods shaped particles and 4.21% for nanospheres. These values were significantly higher than the 3.90% PCE obtained with commercial Degussa VP20 ZnO nanoparticles.
基金European Union’s Horizon 2020 research and innovation program under grant agreement no.[766726]。
文摘The measurement of the magnetic anisotropy of[Fe{(3,5-(CH_(3))_(2)Pz)_(3)BH}_(2)],where Pz=pyrazole,in its high spin state(S=2)by X-ray Magnetic Circular Dichroism(XMCD)spectroscopy when assembled as an organized monolayer on Cu(111)shows the presence of a hard axis of magnetization(positive axial zero-field splitting-ZFS-parameter D).Combining magnetization and multifrequency electron paramagnetic resonance spectroscopy on a reference compound,[Fe{(3-(Ph)Pz)_(3)BH}_(2)],of the same family and ab initio wave function based theoretical calculations,we demonstrate that the magnetic anisotropy of the assembled molecules is not affected when they are present at the substrate/vacuum interface.Comparing our results with those of a reported complex having an almost identical FeN_(6)coordination sphere but an easy axis of magnetization(corresponding to a negative D value),we show that the nature of the magnetic anisotropy(easy/hard axis)is governed by the torsion angle(Ψ)defined by the relative orientation of the pyrazole five-membered rings to the pseudo three-fold axis of the molecules.The rigidity of the(Pz)_(3)BH tridentate ligands,where the three pyrazole moieties are held by the BH group,allows only very slight changes in the torsion angle even when the molecules are in a dissymmetric environment such as an interface.This is the origin of the robust magnetic anisotropy of this family of compounds.
基金financial support from Project NQSTI—ID PE_00000023 funded by the European Union under the Next Generation EU program-CUP H43C22000870001 Spoke 6.A.Z.,M.F.and M.C.would like to thank C.De Angelis and D.Rocco for insightful discussions.
文摘Optical metasurfaces allow complex light manipulation within subwavelength thicknesses and are thus rapidly emerging as a key enabling technology for nanophotonics applications.The control over light polarization already provided a route towards ultracompact metasurface-based polarimetry devices.If translated to the nonlinear optical regime it may become a transformative tool for nonlinear imaging,optical holography,and sensing.Here,we report ultrafast all-optical polarization modulation of upconverted light by all-dielectric metasurfaces via nonlinear interferometry.By controlling the relative phase between a pump beam atωand its frequency-doubled replica at 2ω,we can set the phase relation between two frequency-degenerate upconversion processes at 3ω–sum-frequency generation and third-harmonic generation–stemming from an AlGaAs metasurface.By leveraging the opposite parity of the two nonlinear processes and adjusting their relative intensities,we achieve a modulation of the polarization state of the upconverted light between linear and circular states with a circular polarization degree of up to 83%.Remarkably,circularly polarized light of opposite handedness is symmetrically mapped in the Fourier space,at coincidence with the first diffraction orders of the metasurface.Furthermore,the handedness can be completely reversed within the same diffraction order by applying a phase delay ofπ.Our work adds an additional modulation layer beyond intensity to all-optical routing with precise phase control:polarization.The capability to encode and modulate simultaneously different polarization states in the k-space holds potential for chiral sensing and advanced imaging techniques.
基金The authors acknowledge the use of the Australian National Fabrication Facility(ANFF),ACT Node.Rocio CamachoMorales acknowledges a grant from the Consejo Nacional de Ciencia y Tecnología(CONACYT),MexicoNikolay Dimitrov and Lyubomir Stoyanov acknowledge a grant from the EU Marie-Curie RISE program NOCTURNO+1 种基金Mohsen Rahmani acknowledges support from the UK Research and Innovation Future Leaders Fellowship(MR/T040513/1)Dragomir N.Neshev acknowledges a grant from the Australian Research Council(CE20010001,DP190101559).
文摘Infrared imaging is a crucial technique in a multitude of applications,including night vision,autonomous vehicle navigation,optical tomography,and food quality control.Conventional infrared imaging technologies,however,require the use of materials such as narrow bandgap semiconductors,which are sensitive to thermal noise and often require cryogenic cooling.We demonstrate a compact all-optical alternative to perform infrared imaging in a metasurface composed of GaAs semiconductor nanoantennas,using a nonlinear wave-mixing process.We experimentally show the upconversion of short-wave infrared wavelengths via the coherent parametric process of sum-frequency generation.In this process,an infrared image of a target is mixed inside the metasurface with a strong pump beam,translating the image from the infrared to the visible in a nanoscale ultrathin imaging device.Our results open up new opportunities for the development of compact infrared imaging devices with applications in infrared vision and life sciences.
基金support from European Union's Horizon 2020 research and innovation programme under the HORIZON EUROPE Marie Sklodowska-Curie Actions grant agreement No.665850Paris Ile-de-France Région in the framework of DIM SIRTEQ(LION project)+3 种基金Ville de Paris Emergence program(LATTICE project)IdEx UniversitéParis Cité(ANR-18-IDEX-0001)Labex SEAM(Science and Engineering for Advanced Materials and Devices,ANR-10-LABX-0096)the French RENATECHnetwork.
文摘We demonstrate a chip-integrated semiconductor source that combines polarization and frequency entanglement,allowing the generation of entangled biphoton states in a hybrid degree of freedom without post-manipulation.Our Al Ga As device is based on type-Ⅱ spontaneous parametric downconversion in a counterpropagating phasematching scheme in which the modal birefringence lifts the degeneracy between the two possible nonlinear interactions. This allows the direct generation of polarization–frequency entangled photons at room temperature and telecom wavelength, and in two distinct spatial modes, offering enhanced flexibility for quantum information protocols. The state entanglement is quantified by a combined measurement of the joint spectrum and Hong–Ou–Mandel interference(raw visibility 70.1% ± 1.1%) of the biphotons, allowing to reconstruct a restricted density matrix in the hybrid polarization–frequency space.
基金Part of this work was performed at the Stanford Nano Shared Facilities(SNSF)supported by the National Science Foundation under award ECCS-1542152+2 种基金C.W.was supported by a grant[EP/R02992X/1]from the UK Engineering and Physical Sciences Research Council(EPSRC)This work was performed using resources provided by the ARCHER UK National Supercomputing Service and the Cambridge Service for Data-Driven Discovery(CSD3)operated by the University of Cambridge Research Computing Service(www.csd3.cam.ac.uk),provided by Dell EMC and Intel using Tier-2 funding from the Engineering and Physical Sciences Research Council(capital grant[EP/P020259/1])DiRAC funding from the Science and Technology Facilities Council(www.dirac.ac.uk).C.W.and D.B.are grateful to Antoine George,Nicola Bonini,and Francesco Macheda for insightful discussions.C.J.P.acknowledges the support of a Royal Society Wolfson Research Merit award.E.F.and D.B.thank Matteo Coccioni and Iurii Timrov for useful insights.
文摘Double perovskite oxides,with generalized formula A_(2)BB'O_(6),attract wide interest due to their multiferroic and charge transfer properties.They offer a wide range of potential applications such as spintronics and electrically tunable devices.However,great practical limitations are encountered,since a spontaneous order of the B-site cations is notoriously hard to achieve.In this joint experimental-theoretical work,we focused on the characterization of double perovskites La2TiFeO6 and La_(2)VCuO_(6) films grown by pulsed laser deposition and interpretation of the observed B-site disorder and partial charge transfer between the B-site ions.A random structure sampling method was used to show that several phases compete due to their corresponding configurational entropy.In order to capture a representative picture of the most relevant competing microstates in realistic experimental conditions,this search included the potential formation of non-stoichiometric phases as well,which could also be directly related to the observed partial charge transfer.We optimized the information encapsulated in the potential energy landscape,captured via structure sampling,by evaluating both enthalpic and entropic terms.These terms were employed as a metric for the competition of different phases.This approach,applied herein specifically to La_(2)TiFeO_(6),highlights the presence of highly entropic phases above the ground state which can explain the disorder observed frequently in the broader class of double perovskite oxides.
基金funding from the European Union Horizon 2020 Research and Innovation program under grant agreement no.899673This work reflects only authors’view and the European Commission is not responsible for any use that may be made of the information it contains.G.D.V.acknowledges the support from the HOTMETA project under the PRIN 2022 MUR program funded by the European Union—Next Generation EU—“PNRR-M4C2,investimento 1.1—“Fondo PRIN 2022”—HOT-carrier METasurfaces for Advanced photonics(HOTMETA)+1 种基金contract no.2022LENW33—CUP:D53D23002290006”.A.S.,G.C.,M.M.and G.D.V.acknowledge financial support by the European Union’s NextGenerationEU Programme with the I-PHOQS Infrastructure[IR0000016,ID D2B8D520,CUP B53C22001750006]“Integrated infrastructure initiative in Photonic and Quantum Sciences”.The work is partly supported by the French RENATECH networksupport by the European Union-NextGenerationEU,through the National Recovery and Resilience Plan of the Republic of Bulgaria,SUMMIT BG-RRP-2.004-0008-C0.DN acknowledges the support of the Australian Research Council(CE200100010).
文摘Switching of light polarization on the sub-picosecond timescale is a crucial functionality for applications in a variety of contexts,including telecommunications,biology and chemistry.The ability to control polarization at ultrafast speed would pave the way for the development of unprecedented free-space optical links and of novel techniques for probing dynamical processes in complex systems,as chiral molecules.Such high switching speeds can only be reached with an all-optical paradigm,i.e.,engineering active platforms capable of controlling light polarization via ultrashort laser pulses.Here we demonstrate giant modulation of dichroism and birefringence in an all-dielectric metasurface,achieved at low fluences of the optical control beam.This performance,which leverages the many degrees of freedom offered by all-dielectric active metasurfaces,is obtained by combining a high-quality factor nonlocal resonance with the giant third-order optical nonlinearity dictated by photogenerated hot carriers at the semiconductor band edge.
