Recent progress in the design and fabrication of thermal metasurfaces allows a broad control of the properties of light emission,including its polarization state.Stokes polarimetry is a key approach to accurately char...Recent progress in the design and fabrication of thermal metasurfaces allows a broad control of the properties of light emission,including its polarization state.Stokes polarimetry is a key approach to accurately characterize partially polarized light.The quality of a Stokes polarimeter made of retarders and polarizers can be evaluated by use of metrics such as the equally weighted variance or the condition number of the matrix representing the polarimeter.Although specific instrument configurations are used to maximize polarimeter performance at a given wavelength,such optimal solutions are not spectrally robust because of the wave-length dependence of retardance.This becomes an issue in characterizing broadband thermal sources in the infrared.We report a Stokes polarimeter making use of five polarization analysis states and consisting of two simple and common optical elements—a crystalline waveplate and a linear polarizer.We combine this setup with a Fourier transform infrared spectrometer to measure accurately in a single set of acqui-sitions without requiring any spectral filtering,and to measure the polarization state with accuracy over a broad range of wavelengths.Such a Stokes polarimeter allows for close to optimal noise in the data reduc-tion process in the mid-wave infrared spectral range from 2.5 to 5μm.展开更多
Poly[2-methoxy-5-（20-ethylhexyloxy）-io-phenylenevinylene] （MEH-PPV）, [6,6]-phenyl-C61-butyric acid methyl ester （PCBM） and titanium dioxide （TiO2） nanoparticles （n-type） were dissolved, mixed and deposited b...Poly[2-methoxy-5-（20-ethylhexyloxy）-io-phenylenevinylene] （MEH-PPV）, [6,6]-phenyl-C61-butyric acid methyl ester （PCBM） and titanium dioxide （TiO2） nanoparticles （n-type） were dissolved, mixed and deposited by physical methods （spin-coating） on indium tin-oxide （ITO） substrate. The incorporation of the titanium dioxide nanoparticles changed the morphology and increased the roughness of polymers film （MEH-PPV/PCBM）, and the photocurrent density of the composite （MEH-PPV/PCBM ＋n-TiO2） was higher than that of single MEH- PPV/PCBM film. The study showed that the presence of n-TiO2 particles in the polymeric film improves the photoelectrochemical properties of M EH-PPV/PCBM composite.展开更多
Polarimetry encompasses a collection of optical techniques broadly used in a variety of fields.Nowadays,such techniques have provided their suitability in the biomedical field through the study of the polarimetric res...Polarimetry encompasses a collection of optical techniques broadly used in a variety of fields.Nowadays,such techniques have provided their suitability in the biomedical field through the study of the polarimetric response of biological samples(retardance,dichroism and depolarization)by measuring certain polarimetric observables.One of these features,depolarization,is mainly produced by scattering on samples,which is a predominant efiect in turbid media as biological tissues.In turn,retardance and dichroic efiects are produced by tissue anisotropies and can lead to depolarization too.Since depolarization is a predominant efiect in tissue samples,we focus on studying difierent depolarization metrics for biomedical applications.We report the suitability of a set of depolarizing observables,the indices of polarimetric purity(IPPs),for biological tissue inspection.We review some results where we demonstrate that IPPs lead to better performance than the depolarization index,which is a well-established and commonly used depolarization observable in the literature.We also provide how IPPs are able to significantly enhance contrast between difierent tissue structures and even to reveal structures hidden by using standard intensity images.Finally,we also explore the classificatory potential of IPPs and other depolarizing observables for the discrimination of difierent tissues obtained from ex vivo chicken samples(muscle,tendon,myotendinous junction and bone),reaching accurate models for tissue classification.展开更多
An object that possesses chirality,that is,having its mirror image not overlayed on itself by rotation and translation,can provide a different optical response to a left-or right-handed circular polarized light.Chiral...An object that possesses chirality,that is,having its mirror image not overlayed on itself by rotation and translation,can provide a different optical response to a left-or right-handed circular polarized light.Chiral nanostructures may exhibit polarization-selective optical properties that can be controlled for micro-to-nano optical element engineering.An attractive way to induce such complex nanostructures in three-dimension in glass is femtosecond laser direct writing.However,the mechanism of femtosecond laser induced chirality remains to be unveiled due to complex physical and chemical processes occurring during the ultrashort light-matter interaction.Here,a phenomenological model is proposed and is built on two-layers phase shifters to account for this laser-induced optical chirality in an initially achiral material(silica glass).This model is based on the observation that femtosecond laser induced nanogratings own two principal contributions to its aggregate birefringent response:a form and a stress-related one.By refining this formalism,a multilayer approach is developed to imprint on demand optical rotation.Values up to+/-60°at 550 nm within an optimal 80μm thickness in silica glass are possible,corresponding to the highest value in a glass to date.These results provide new insights of circular-optical control in micro-nano optical manufacturing and open new opportunities for photonics applications.展开更多
A comprehensive picture of the initial stages of silicene growth on graphite is drawn.Evidence is shown that quasiparticle interferences play a crucial role in the formation of the observed silicene configurations.We ...A comprehensive picture of the initial stages of silicene growth on graphite is drawn.Evidence is shown that quasiparticle interferences play a crucial role in the formation of the observed silicene configurations.We propose,on one hand,that the charge modulations caused by those quantum interferences serve as templates and guide the incoming Si atoms to self-assemble to the unique(√3 x√3)R30°honeycomb atomic arrangement.On the other hand,their limited extension limits the growth to about 150 Si atoms under our present deposition conditions.The here proposed electrostatic interaction finally explains the unexpected stability of the observed silicene islands over time and with temperature.Despite the robust guiding nature of those quantum interferences during the early growth phase,we demonstrate that the window of experimental conditions for silicene growth is quite narrow,making it an extremely challenging experimental task.Finally,it is shown that the experimentally observed threedimensional silicon clusters might very well be the simple result of the end of the silicene growth resulting from the limited extent of the quasi-particle interferences.展开更多
We describe the mechanical properties of turbostratically graphitized carbon films obtained by carbon laser-patterning(CLaP)and their application as bending or mechanical pressure sensors.Stable conductive carbonized ...We describe the mechanical properties of turbostratically graphitized carbon films obtained by carbon laser-patterning(CLaP)and their application as bending or mechanical pressure sensors.Stable conductive carbonized films were imprinted on a flexible polyethylene terephthalate(PET)substrate by laser-induced carbonization.After initial gentle bending,i.e.training,these spongelike porous films show a quantitative and reversible change in resistance upon bending or application of pressure in normal loading direction.Maximum response values ofΔR/R0=388%upon positive bending(tensile stress)and−22.9%upon negative bending(compression)are implicit for their high sensitivity towards mechanical deformation.Normal mechanical loading in a range between 0 and 500 kPa causes a response betweenΔR/R_(0)=0 and−15%.The reversible increase or decrease in resistance is attributed to compression or tension of the turbostratically graphitized domains,respectively.This mechanism is supported by a detailed microstructural and chemical high-resolution transmission electron microscopic analysis of the cross-section of the laserpatterned carbon.展开更多
文摘Recent progress in the design and fabrication of thermal metasurfaces allows a broad control of the properties of light emission,including its polarization state.Stokes polarimetry is a key approach to accurately characterize partially polarized light.The quality of a Stokes polarimeter made of retarders and polarizers can be evaluated by use of metrics such as the equally weighted variance or the condition number of the matrix representing the polarimeter.Although specific instrument configurations are used to maximize polarimeter performance at a given wavelength,such optimal solutions are not spectrally robust because of the wave-length dependence of retardance.This becomes an issue in characterizing broadband thermal sources in the infrared.We report a Stokes polarimeter making use of five polarization analysis states and consisting of two simple and common optical elements—a crystalline waveplate and a linear polarizer.We combine this setup with a Fourier transform infrared spectrometer to measure accurately in a single set of acqui-sitions without requiring any spectral filtering,and to measure the polarization state with accuracy over a broad range of wavelengths.Such a Stokes polarimeter allows for close to optimal noise in the data reduc-tion process in the mid-wave infrared spectral range from 2.5 to 5μm.
文摘Poly[2-methoxy-5-（20-ethylhexyloxy）-io-phenylenevinylene] （MEH-PPV）, [6,6]-phenyl-C61-butyric acid methyl ester （PCBM） and titanium dioxide （TiO2） nanoparticles （n-type） were dissolved, mixed and deposited by physical methods （spin-coating） on indium tin-oxide （ITO） substrate. The incorporation of the titanium dioxide nanoparticles changed the morphology and increased the roughness of polymers film （MEH-PPV/PCBM）, and the photocurrent density of the composite （MEH-PPV/PCBM ＋n-TiO2） was higher than that of single MEH- PPV/PCBM film. The study showed that the presence of n-TiO2 particles in the polymeric film improves the photoelectrochemical properties of M EH-PPV/PCBM composite.
基金the financial support of Spanish MINECO(PID2021-126509OB-C21,and Fondos FEDER)Catalan Government(2017-SGR-001500).
文摘Polarimetry encompasses a collection of optical techniques broadly used in a variety of fields.Nowadays,such techniques have provided their suitability in the biomedical field through the study of the polarimetric response of biological samples(retardance,dichroism and depolarization)by measuring certain polarimetric observables.One of these features,depolarization,is mainly produced by scattering on samples,which is a predominant efiect in turbid media as biological tissues.In turn,retardance and dichroic efiects are produced by tissue anisotropies and can lead to depolarization too.Since depolarization is a predominant efiect in tissue samples,we focus on studying difierent depolarization metrics for biomedical applications.We report the suitability of a set of depolarizing observables,the indices of polarimetric purity(IPPs),for biological tissue inspection.We review some results where we demonstrate that IPPs lead to better performance than the depolarization index,which is a well-established and commonly used depolarization observable in the literature.We also provide how IPPs are able to significantly enhance contrast between difierent tissue structures and even to reveal structures hidden by using standard intensity images.Finally,we also explore the classificatory potential of IPPs and other depolarizing observables for the discrimination of difierent tissues obtained from ex vivo chicken samples(muscle,tendon,myotendinous junction and bone),reaching accurate models for tissue classification.
基金Agence Nationale pour la Recherche,FLAG-IR project,grant number ANR-18-CE08-0004-01d CNRS Défi Instrumentation aux Limites,UltraBragg project,Science and Technology Commission of Shanghai Municipality(20JC1415700)+1 种基金Jiafeng Lu acknowledges the China Scholarship Council(CSC)for the funding No.202006890077We greatly acknowledge Dr.Maxime Cavillon for valuable discussions.
文摘An object that possesses chirality,that is,having its mirror image not overlayed on itself by rotation and translation,can provide a different optical response to a left-or right-handed circular polarized light.Chiral nanostructures may exhibit polarization-selective optical properties that can be controlled for micro-to-nano optical element engineering.An attractive way to induce such complex nanostructures in three-dimension in glass is femtosecond laser direct writing.However,the mechanism of femtosecond laser induced chirality remains to be unveiled due to complex physical and chemical processes occurring during the ultrashort light-matter interaction.Here,a phenomenological model is proposed and is built on two-layers phase shifters to account for this laser-induced optical chirality in an initially achiral material(silica glass).This model is based on the observation that femtosecond laser induced nanogratings own two principal contributions to its aggregate birefringent response:a form and a stress-related one.By refining this formalism,a multilayer approach is developed to imprint on demand optical rotation.Values up to+/-60°at 550 nm within an optimal 80μm thickness in silica glass are possible,corresponding to the highest value in a glass to date.These results provide new insights of circular-optical control in micro-nano optical manufacturing and open new opportunities for photonics applications.
文摘A comprehensive picture of the initial stages of silicene growth on graphite is drawn.Evidence is shown that quasiparticle interferences play a crucial role in the formation of the observed silicene configurations.We propose,on one hand,that the charge modulations caused by those quantum interferences serve as templates and guide the incoming Si atoms to self-assemble to the unique(√3 x√3)R30°honeycomb atomic arrangement.On the other hand,their limited extension limits the growth to about 150 Si atoms under our present deposition conditions.The here proposed electrostatic interaction finally explains the unexpected stability of the observed silicene islands over time and with temperature.Despite the robust guiding nature of those quantum interferences during the early growth phase,we demonstrate that the window of experimental conditions for silicene growth is quite narrow,making it an extremely challenging experimental task.Finally,it is shown that the experimentally observed threedimensional silicon clusters might very well be the simple result of the end of the silicene growth resulting from the limited extent of the quasi-particle interferences.
基金support from the Fonds der Chemischen Industrie and the Max Planck Society.
文摘We describe the mechanical properties of turbostratically graphitized carbon films obtained by carbon laser-patterning(CLaP)and their application as bending or mechanical pressure sensors.Stable conductive carbonized films were imprinted on a flexible polyethylene terephthalate(PET)substrate by laser-induced carbonization.After initial gentle bending,i.e.training,these spongelike porous films show a quantitative and reversible change in resistance upon bending or application of pressure in normal loading direction.Maximum response values ofΔR/R0=388%upon positive bending(tensile stress)and−22.9%upon negative bending(compression)are implicit for their high sensitivity towards mechanical deformation.Normal mechanical loading in a range between 0 and 500 kPa causes a response betweenΔR/R_(0)=0 and−15%.The reversible increase or decrease in resistance is attributed to compression or tension of the turbostratically graphitized domains,respectively.This mechanism is supported by a detailed microstructural and chemical high-resolution transmission electron microscopic analysis of the cross-section of the laserpatterned carbon.
