Active control of terahertz(THz)waves is attracting tremendous attentions in terahertz communications and active photonic devices.Perovskite,due to its excellent photoelectric conversion performance and simple manufac...Active control of terahertz(THz)waves is attracting tremendous attentions in terahertz communications and active photonic devices.Perovskite,due to its excellent photoelectric conversion performance and simple manufacturing process,has emerged as a promising candidate for optoelectronic applications.However,the exploration of perovskites in optically controlled THz modulators is still limited.In this work,the photoelectric properties and carrier dynamics of FA_(0.4)MA_(0.6)PbI_(3)perovskite films were investigated by optical pumped terahertz probe(OPTP)system.The ultrafast carrier dynamics reveal that FA_(0.4)MA_(0.6)PbI_(3)thin film exhibits rapid switching and relaxation time within picosecond level,suggesting that FA_(0.4)MA_(0.6)PbI_(3)is an ideal candidate for active THz devices with ultrafast response.Furthermore,as a proof of concept,a FA_(0.4)MA_(0.6)PbI_(3)-based metadevice with integrating plasma-induced transparency(PIT)effect was fabricated to achieve ultrafast modulation of THz wave.The experimental results demonstrated that the switching time of FA_(0.4)MA_(0.6)PbI_(3)-based THz modulator is near to 3.5 ps,and the threshold of optical pump is as low as 12.7μJ cm^(-2).The simulation results attribute the mechanism of ultrafast THz modulation to photo-induced free carriers in the FA_(0.4)MA_(0.6)PbI_(3)layer,which progressively shorten the capacitive gap of PIT resonator.This study not only illuminates the potential of FA_(0.4)MA_(0.6)PbI_(3)in THz modulation,but also contributes to the field of ultrafast photonic devices.展开更多
Acoustic streaming enabled by a Lamb wave resonator(LWR)is efficient for particle trapping and enrichment in microfluidic channels.However,because Lamb waves combine the features of bulk acoustic waves and surface aco...Acoustic streaming enabled by a Lamb wave resonator(LWR)is efficient for particle trapping and enrichment in microfluidic channels.However,because Lamb waves combine the features of bulk acoustic waves and surface acoustic waves,the resulting acoustic streaming in the LWR occurs in multiple planes,and the particle flow behavior in this acoustofluidic system is largely unknown.Reported here are numerical simulations and laboratory experiments conducted to investigate the boundary conditions for particle motion inside a microvortex induced by an LWR.Upon dynamic capture,the particles’trajectories become orbital paths within an acoustic vortex.The suspended particles encounter two distinct acoustic phenomena,i.e.,the drag force resulting from acoustic streaming and the acoustic radiation force,which exert forces in various directions on the particles.When the acoustic radiation force and the fluid drag force are dominant for large and small particles in a mixed solution,respectively,the large particles reside within the vortex while the small particles remain at its periphery.Conversely,when the acoustic radiation force is dominant for both types of particles,the distribution pattern is reversed.展开更多
The far-infrared optical properties of melamine and its deuterated isotope,melamine-d_6 were experimentally and theoretically investigated in the frequency range from 0.2 to 3.0 THz.Under the room temperature and dry ...The far-infrared optical properties of melamine and its deuterated isotope,melamine-d_6 were experimentally and theoretically investigated in the frequency range from 0.2 to 3.0 THz.Under the room temperature and dry air nitrogen conditions,three absorption bands were observed at 2.0,2.3 and 2.6 THz in the melamine sample by use of terahertz time-domain spectroscopy.Whereas,in the melamine-d_6 sample,the observed absorption bands shift towards lower frequencies and the relative intensity of the absorption bands reduces.Numerical simulation results based on the Parameterized Model number 3(PM3) were compared with the experimental data and the observed vibration spectra were assigned according to the PM3 calculations.The absorption bands of the measured melamine samples at terahertz frequencies are highly correlated with the intermolecular hydrogen bond stretching and π-π stacking vibration.Also,the red shift of the absorption bands is due to hydrogen/deuterium substitution.展开更多
We present a linear-cavity stretched-pulse fibre laser and by semiconductor saturable-absorber mirrors. A with mode locking by a nonlinear polarization rotation Q-switched mode-locking cw train and a mode-locking puls...We present a linear-cavity stretched-pulse fibre laser and by semiconductor saturable-absorber mirrors. A with mode locking by a nonlinear polarization rotation Q-switched mode-locking cw train and a mode-locking pulse train are obtained in the experiment. We investigate the effects of the equivalent fast saturable absorber and the slow saturable absorbers in experiment. It is found that neither the nonlinear polarization evolution effect nor a semiconductor saturable absorber mirror is enough to produce the stable cw mode-locking pulses in this experiment. A nonlinear polarization evolution effect controls the cavity loss to literally carve the pulses; semiconductor saturable absorber mirrors provide the self-restarting and maintain the stability of the modelocking operation.展开更多
Optoelectronic terahertz generation and detection play a key role in the applications of non-destructive testing,which involves different areas such as physics,biological,material science,imaging,explosions detection,...Optoelectronic terahertz generation and detection play a key role in the applications of non-destructive testing,which involves different areas such as physics,biological,material science,imaging,explosions detection,astronomy applications,semiconductor technology and superconductiong electronics. In this article,we present a reviewof the principle and performance of typical terahertz sources,detectors and non-destructive testing applications. On this basis,the newdevelopment and trends of terahertz radiation detectors are also discussed.展开更多
Plasmonic vortices confining orbital angular momentums to surface have aroused wide research interest in the last decade.Recent advances of near-field microscopes have enabled the study on the spatiotemporal dynamics ...Plasmonic vortices confining orbital angular momentums to surface have aroused wide research interest in the last decade.Recent advances of near-field microscopes have enabled the study on the spatiotemporal dynamics of plasmonic vortices,providing a better understanding of optical orbital angular momentums in the evanescent wave regime.However,these works only focused on the objective characterization of plasmonic vortex and have not achieved subjectively tailoring of its spatiotemporal dynamics for specific applications.Herein,it is demonstrated that the plasmonic vortices with the same topological charge can be endowed with distinct spatiotemporal dynamics by simply changing the coupler design.Based on a near-field scanning terahertz microscopy,the surface plasmon fields are directly obtained with ultrahigh spatiotemporal resolution,experimentally exhibiting the generation and evolution divergences during the whole lifetime of plasmonic vortices.The proposed strategy is straightforward and universal,which can be readily applied into visible or infrared frequencies,facilitating the development of plasmonic vortex related researches and applications.展开更多
Based on the full-vector plane-wave method (FVPWM), a hollow-core photonic crystal fibre (HC-PCF) fabricated by using the improved stack-and-draw technique is simulated. Under given propagation constants β, sever...Based on the full-vector plane-wave method (FVPWM), a hollow-core photonic crystal fibre (HC-PCF) fabricated by using the improved stack-and-draw technique is simulated. Under given propagation constants β, several effective photonie band gaps with different sizes emerge within the visible wavelength range from 575 to 720 nm. The fundamental mode and second-order mode lying in a part of PBGs are investigated. In the transmission spectrum tested, the positions of PBGs are discovered to be shifting to shorter wavelengths. The main reason is the existence of interstitial holes at nodes in the cladding region. In the later experiment, green light is observed propagating in the air-core region, and the result is more consistent with our theoretical simulation.展开更多
The presence of chemical warfare agents(CWAs)in the environment is a serious threat to human safety,but there are many problems with the currently available detection methods for CWAs.For example,gas chromatography–m...The presence of chemical warfare agents(CWAs)in the environment is a serious threat to human safety,but there are many problems with the currently available detection methods for CWAs.For example,gas chromatography–mass spectrometry cannot be used for in-field detection owing to the rather large size of the equipment required,while commercial sensors have the disadvantages of low sensitivity and poor selectivity.Here,we develop a portable gas sensing instrument for CWA detection that consists of a MEMSfabricated micro-preconcentrator(μPC)and a film bulk acoustic resonator(FBAR)gas sensor.The μPC is coated with a nanoporous metal–organic framework material to enrich the target,while the FBAR provides rapid detection without the need for extra carrier gas.Dimethyl methylphosphonate(DMMP),a simulant of the chemical warfare agent sarin,is used to test the performance of the instrument.Experimental results show that the μPC provides effective sample pretreatment,while the FBAR gas sensor has good sensitivity to DMMP vapor.The combination of μPC and FBAR in one instrument gives full play to their respective advantages,reducing the limit of detection of the analyte.Moreover,both the μPC and the FBAR are fabricated using a CMOS-compatible approach,and the prototype instrument is compact in size with high portability and thus has potential for application to in-field detection of CWAs.展开更多
For a typical photonic crystal fiber with two zero-dispersion wavelengths,we theoretically demonstrate a new way to generate supercontinuum using an input pulse of 30fs duration and lOkW peak power for providing a com...For a typical photonic crystal fiber with two zero-dispersion wavelengths,we theoretically demonstrate a new way to generate supercontinuum using an input pulse of 30fs duration and lOkW peak power for providing a compact and cost effective light source to the ultra-broadband time-resolved coherent anti-Stokes Raman scattering spectroscopy.展开更多
Metal-dielectric subwavelength gratings under s-polarized and p-polarized visible radiation are studied for discovering their intriguing behaviors of spectral resonance and color property.The dependence of their reson...Metal-dielectric subwavelength gratings under s-polarized and p-polarized visible radiation are studied for discovering their intriguing behaviors of spectral resonance and color property.The dependence of their resonance and color on grating parameters as well as angle of incidence and position of plane of incidence is also analyzed.For s-polarized light,the behavior of spectral resonance with single peak and higher peak efficiency is found.While transmission spectra for p-polarized light are not able to achieve a behavior like that of s-polarization,creating a perceived color is feasible.Moreover,a security grating with distinctive color shifts has been designed and its resonant properties as well as related color variation have also been provided.展开更多
It has been almost 50 years since the term“brain–computer interface”(BCI)was first proposed by Jacques J.Vidal in 1973[1].Unlike traditional electronic interfaces that transmit nonliving information between devices...It has been almost 50 years since the term“brain–computer interface”(BCI)was first proposed by Jacques J.Vidal in 1973[1].Unlike traditional electronic interfaces that transmit nonliving information between devices,BCIs set up a communication bridge between a living brain and nonliving devices.Technically speaking,a BCI is a system that measures brain activity and converts it into the artificial outputs that replace,restore,enhance,supplement,or improve the natural central nervous system outputs[2].At present,electroencephalography(EEG)is the most commonly used brain signal for BCIs.展开更多
Passively Q-switched quasi-continuous-wave (QCW) diode-pumped Nd:YAG laser with Cr^4+ :YAG as saturable absorber is numerically investigated by solving the coupled rate equations. The threshold pump rate for pass...Passively Q-switched quasi-continuous-wave (QCW) diode-pumped Nd:YAG laser with Cr^4+ :YAG as saturable absorber is numerically investigated by solving the coupled rate equations. The threshold pump rate for passively Q-switched QCW-pumped laser is derived. The effects of the pump rate and pump-pulse duration on the laser operation characteristics are studied theoretically. The pump power range can be estimated according to the number of output pulses. The numerical simulation results are in good agreement with the experimental results.展开更多
We propose a novel technique for generating intense few to mono-cycle femtosecond pulses. The simulation demonstrate that for the temperature difference of 300K, the spectrum of the output pulses is increased by 67% a...We propose a novel technique for generating intense few to mono-cycle femtosecond pulses. The simulation demonstrate that for the temperature difference of 300K, the spectrum of the output pulses is increased by 67% and the transform limited pulse width is reduced almost by half, compared with those obtained with hollow fibres in uniform temperature.展开更多
A compact, efficient and high-power laser diode (LD) single-end-pumped Nd:YVO4 laser with continuous-wave emission at 1342 nm is reported. With a single crystal single-end-pumped by fibre-coupled LD array, an outpu...A compact, efficient and high-power laser diode (LD) single-end-pumped Nd:YVO4 laser with continuous-wave emission at 1342 nm is reported. With a single crystal single-end-pumped by fibre-coupled LD array, an output power of 7.36W is obtained from the laser cavity of concave-convex shape, corresponding to an optical-to-optical efficiency of 32.8%. The laser is operated in TEM00 mode with small rms amplitude noise of 0.3%. The influences of the Nd concentration, transmissivity of the output mirror and the cavity length on the output power have been studied experimentally.展开更多
Photoacoustic mesoscopy(PAMe) offers high-sensitivity in vivo imaging based on the rich optical contrast in biological tissues,with sub-100-micron resolutions at a few millimeters depth. By benefiting from low ultraso...Photoacoustic mesoscopy(PAMe) offers high-sensitivity in vivo imaging based on the rich optical contrast in biological tissues,with sub-100-micron resolutions at a few millimeters depth. By benefiting from low ultrasonic scattering,this emerging technology has pushed the penetration depth beyond the optical diffuse limit unprecedented for high-resolution optical methods.Here,we review ed the state-of-art implementations of PAMe and their achievements in biological and primary clinical applications. With the high-frequency focused ultrasonic detector,the high-resolution optical visualization can be achieved by utilizing various PAMe systems. These capabilities of PAMe have made it well applicable for understanding the biological mechanisms,exploring the pathological features and analyzing the characteristics of human skin. Future improvements and prospects of PAMe are also mentioned,suggesting its great potential tow ards the corresponding emerging biomedical and clinical applications.展开更多
This paper presents a set of equations describing the terahertz generation and electro-optic detection based on optical rectification in zincblende crystals. The dependence of terahertz emission efficiency on the pola...This paper presents a set of equations describing the terahertz generation and electro-optic detection based on optical rectification in zincblende crystals. The dependence of terahertz emission efficiency on the polarization of incident beam and crystal-orientation is discussed. For the experimental setup with a transceiver which transmits and detects terahertz radiation in the same crystal, we have demonstrated the optimal combination of both parameters above to optimize the working efficiency. Equations supplied in this paper are valid for zincblende crystals with arbitrary crystal- orientation and every possible polarization of an incident beam, which are of great significance for the optimization of a system.展开更多
Usually,only focused femtosecond(fs)lasers at near-infrared(NIR)range can induce photo-damage to transparent cells,making it difficult to treat large amount of cells by such optical methods for photostimulation.In thi...Usually,only focused femtosecond(fs)lasers at near-infrared(NIR)range can induce photo-damage to transparent cells,making it difficult to treat large amount of cells by such optical methods for photostimulation.In this study,we clarify the mechanism of photodamage to cells that are co-cultured with gold nanorods(GNRs)by fs laser.The pulse duration and repetition rate of the fs laser play a key role in cell damage suggesting that the heat accumulation con-tributes to the major part for the cell damage rather than the high peak power which mainly determines the efficiency of multiphoton excitation.We further show that cellular Ca^(2+)can also be released in this scheme,but the process is more sensitive to peak power.Our results can provide a large-scale GNR-mediated photostimulation for cell signaling modulation.展开更多
This paper numerically simulates the process of ablation of an aluminum target by an intense femtosecond laser with a fluence of 40 J/cm2 based on the two-temperature equation, and obtains the evolution of the free el...This paper numerically simulates the process of ablation of an aluminum target by an intense femtosecond laser with a fluence of 40 J/cm2 based on the two-temperature equation, and obtains the evolution of the free electron temperature and lattice temperature over a large temporal and depth range, for the first time. By investigating the temporal evolution curves of the free electron temperature and lattice temperature at three representative depths of 0, 100 nm and 500 nm, it reveals different characteristics and mechanisms of the free electron temperature evolution at different depths. The results show that, in the intense femtosecond laser ablation of aluminum, the material ablation is mainly induced by the thermal conduction of free electrons, instead of the direct absorption of the laser energy; in addition, the thermal conduction of free electrons and the coupling effect between electrons and lattice will induce the temperature of free electrons deep inside the target to experience a process from increase to decrease and finally to increase again.展开更多
The hemispherical phased transducer maximizes the coverage of the skull and the ultrasonic energy per unit area of the skull is minimized,thereby reducing the risk of skull burns,but the transducer has a small focal a...The hemispherical phased transducer maximizes the coverage of the skull and the ultrasonic energy per unit area of the skull is minimized,thereby reducing the risk of skull burns,but the transducer has a small focal area adjustment range,increasing the focal length of treatment is an urgent question for this type of transducer.In this paper,a three-dimensional high-intensity focused ultrasound(HIFU)transcranial propagation model is established based on the human head structure.The finite difference time domain(FDTD)is combined with the Westervelt acoustic wave nonlinear propagation equation and Penne's biological heat conduction equation for numerical simulation of the sound pressure field and temperature field.Forming a treatable focal area in a small-opening hemispherical transducer with a small amount of numerical simulation calculation focusing at a set position to determine the minimum partial excitation area ratio of focusing.And then,applying these preliminary results to a large-opening diameter hemispherical transducer and the temperature field formed by it or full excitation is studied.The results show that the focus area with the excitation area ratio of less than 22%moves forward to the transducer side when the excitation sound is formed.When the excitation area ratio is greater than or equal to 23%,it focuses at the set position.In the case of partial incentives,using 23%of the partial array,the adjustable range of the treatable focal area formed in the three-dimensional space is larger than that of the full excitation.展开更多
The well-known Fraunhofer multi-slit diffraction is described as the multi-slit interference modulated by the singleslit diffraction, namely the multiplication between the single-slit diffraction factor and the multi-...The well-known Fraunhofer multi-slit diffraction is described as the multi-slit interference modulated by the singleslit diffraction, namely the multiplication between the single-slit diffraction factor and the multi-slit interference factor. By considering the simplified argument we show that the multi-slit diffraction of evanescent waves which are in the near-field region also has the interference and diffraction effects, and that this two-fold effect can be expressed as the convolution of the diffraction factor and the interference factor. Our conclusion could be helpful to understand the contribution of evanescent waves to the optical responses of sub-wavelength structures such as slits and grooves.展开更多
基金supported by the National Natural Science Foundation of China(U1930117,12204445)。
文摘Active control of terahertz(THz)waves is attracting tremendous attentions in terahertz communications and active photonic devices.Perovskite,due to its excellent photoelectric conversion performance and simple manufacturing process,has emerged as a promising candidate for optoelectronic applications.However,the exploration of perovskites in optically controlled THz modulators is still limited.In this work,the photoelectric properties and carrier dynamics of FA_(0.4)MA_(0.6)PbI_(3)perovskite films were investigated by optical pumped terahertz probe(OPTP)system.The ultrafast carrier dynamics reveal that FA_(0.4)MA_(0.6)PbI_(3)thin film exhibits rapid switching and relaxation time within picosecond level,suggesting that FA_(0.4)MA_(0.6)PbI_(3)is an ideal candidate for active THz devices with ultrafast response.Furthermore,as a proof of concept,a FA_(0.4)MA_(0.6)PbI_(3)-based metadevice with integrating plasma-induced transparency(PIT)effect was fabricated to achieve ultrafast modulation of THz wave.The experimental results demonstrated that the switching time of FA_(0.4)MA_(0.6)PbI_(3)-based THz modulator is near to 3.5 ps,and the threshold of optical pump is as low as 12.7μJ cm^(-2).The simulation results attribute the mechanism of ultrafast THz modulation to photo-induced free carriers in the FA_(0.4)MA_(0.6)PbI_(3)layer,which progressively shorten the capacitive gap of PIT resonator.This study not only illuminates the potential of FA_(0.4)MA_(0.6)PbI_(3)in THz modulation,but also contributes to the field of ultrafast photonic devices.
基金support of the National Natural Science Foundation of China (Grant No.62174119)the 111 Project (Grant No.B07014)the Foundation for Talent Scientists of Nanchang Institute for Microtechnology of Tianjin University.
文摘Acoustic streaming enabled by a Lamb wave resonator(LWR)is efficient for particle trapping and enrichment in microfluidic channels.However,because Lamb waves combine the features of bulk acoustic waves and surface acoustic waves,the resulting acoustic streaming in the LWR occurs in multiple planes,and the particle flow behavior in this acoustofluidic system is largely unknown.Reported here are numerical simulations and laboratory experiments conducted to investigate the boundary conditions for particle motion inside a microvortex induced by an LWR.Upon dynamic capture,the particles’trajectories become orbital paths within an acoustic vortex.The suspended particles encounter two distinct acoustic phenomena,i.e.,the drag force resulting from acoustic streaming and the acoustic radiation force,which exert forces in various directions on the particles.When the acoustic radiation force and the fluid drag force are dominant for large and small particles in a mixed solution,respectively,the large particles reside within the vortex while the small particles remain at its periphery.Conversely,when the acoustic radiation force is dominant for both types of particles,the distribution pattern is reversed.
基金supported by the Major Project of the National Natural Science Foundation of China (Grant Nos.60977064 and 61028011)Tianjin Sci-Tech Program(Grant No.07ZCGHHZ01100, Grant No.09ZCKFGX01500,and Grant No.10JCYB JC01400)
文摘The far-infrared optical properties of melamine and its deuterated isotope,melamine-d_6 were experimentally and theoretically investigated in the frequency range from 0.2 to 3.0 THz.Under the room temperature and dry air nitrogen conditions,three absorption bands were observed at 2.0,2.3 and 2.6 THz in the melamine sample by use of terahertz time-domain spectroscopy.Whereas,in the melamine-d_6 sample,the observed absorption bands shift towards lower frequencies and the relative intensity of the absorption bands reduces.Numerical simulation results based on the Parameterized Model number 3(PM3) were compared with the experimental data and the observed vibration spectra were assigned according to the PM3 calculations.The absorption bands of the measured melamine samples at terahertz frequencies are highly correlated with the intermolecular hydrogen bond stretching and π-π stacking vibration.Also,the red shift of the absorption bands is due to hydrogen/deuterium substitution.
文摘We present a linear-cavity stretched-pulse fibre laser and by semiconductor saturable-absorber mirrors. A with mode locking by a nonlinear polarization rotation Q-switched mode-locking cw train and a mode-locking pulse train are obtained in the experiment. We investigate the effects of the equivalent fast saturable absorber and the slow saturable absorbers in experiment. It is found that neither the nonlinear polarization evolution effect nor a semiconductor saturable absorber mirror is enough to produce the stable cw mode-locking pulses in this experiment. A nonlinear polarization evolution effect controls the cavity loss to literally carve the pulses; semiconductor saturable absorber mirrors provide the self-restarting and maintain the stability of the modelocking operation.
基金supported by the Cooperative Innovation Center of Terahertz Science , the National Basic Research Program of China (Grant No. 2014CB339800)the National Natural Science Foundation of China (Grant Nos. 61138001, 61420106006)+1 种基金the Program for Changjiang Scholars and Innovative Research Team in University (grant No. IRT13033)the Major National Development Project of Scientific Instruments and Equipment of China (Grant No. 2011YQ150021)
文摘Optoelectronic terahertz generation and detection play a key role in the applications of non-destructive testing,which involves different areas such as physics,biological,material science,imaging,explosions detection,astronomy applications,semiconductor technology and superconductiong electronics. In this article,we present a reviewof the principle and performance of typical terahertz sources,detectors and non-destructive testing applications. On this basis,the newdevelopment and trends of terahertz radiation detectors are also discussed.
基金supported by the National Natural Science Foundation of China(62005193,62135008,62075158,62025504,61935015)the National Science Foundation(2114103)Guangxi Key Laboratory of Optoelectroric Information Processing(GD20202).
文摘Plasmonic vortices confining orbital angular momentums to surface have aroused wide research interest in the last decade.Recent advances of near-field microscopes have enabled the study on the spatiotemporal dynamics of plasmonic vortices,providing a better understanding of optical orbital angular momentums in the evanescent wave regime.However,these works only focused on the objective characterization of plasmonic vortex and have not achieved subjectively tailoring of its spatiotemporal dynamics for specific applications.Herein,it is demonstrated that the plasmonic vortices with the same topological charge can be endowed with distinct spatiotemporal dynamics by simply changing the coupler design.Based on a near-field scanning terahertz microscopy,the surface plasmon fields are directly obtained with ultrahigh spatiotemporal resolution,experimentally exhibiting the generation and evolution divergences during the whole lifetime of plasmonic vortices.The proposed strategy is straightforward and universal,which can be readily applied into visible or infrared frequencies,facilitating the development of plasmonic vortex related researches and applications.
基金Supported by the National Basic Research Programme of China under Grant No 2003CB314905, and the National Natural Science Foundation of China under Grant No 60637010.
文摘Based on the full-vector plane-wave method (FVPWM), a hollow-core photonic crystal fibre (HC-PCF) fabricated by using the improved stack-and-draw technique is simulated. Under given propagation constants β, several effective photonie band gaps with different sizes emerge within the visible wavelength range from 575 to 720 nm. The fundamental mode and second-order mode lying in a part of PBGs are investigated. In the transmission spectrum tested, the positions of PBGs are discovered to be shifting to shorter wavelengths. The main reason is the existence of interstitial holes at nodes in the cladding region. In the later experiment, green light is observed propagating in the air-core region, and the result is more consistent with our theoretical simulation.
基金The authors gratefully acknowledge financial support from the National Natural Science Foundation of China(NSFC Nos.62174119 and 21861132001)the National Key R&D Program of China(2018YFE0118700)+2 种基金Tianjin Applied Basic Research and Advanced Technology(17JCJQJC43600)the 111 Project(B07014)the Foundation for Talent Scientists of Nanchang Institute for Micro-technology of Tianjin University.
文摘The presence of chemical warfare agents(CWAs)in the environment is a serious threat to human safety,but there are many problems with the currently available detection methods for CWAs.For example,gas chromatography–mass spectrometry cannot be used for in-field detection owing to the rather large size of the equipment required,while commercial sensors have the disadvantages of low sensitivity and poor selectivity.Here,we develop a portable gas sensing instrument for CWA detection that consists of a MEMSfabricated micro-preconcentrator(μPC)and a film bulk acoustic resonator(FBAR)gas sensor.The μPC is coated with a nanoporous metal–organic framework material to enrich the target,while the FBAR provides rapid detection without the need for extra carrier gas.Dimethyl methylphosphonate(DMMP),a simulant of the chemical warfare agent sarin,is used to test the performance of the instrument.Experimental results show that the μPC provides effective sample pretreatment,while the FBAR gas sensor has good sensitivity to DMMP vapor.The combination of μPC and FBAR in one instrument gives full play to their respective advantages,reducing the limit of detection of the analyte.Moreover,both the μPC and the FBAR are fabricated using a CMOS-compatible approach,and the prototype instrument is compact in size with high portability and thus has potential for application to in-field detection of CWAs.
基金Supported by the National Natural Science Foundation of China under Grant No 60627003,and the Foundation for Creative Team in Institution of Higher Education of Guangdong Province(No 06CXTD009).
文摘For a typical photonic crystal fiber with two zero-dispersion wavelengths,we theoretically demonstrate a new way to generate supercontinuum using an input pulse of 30fs duration and lOkW peak power for providing a compact and cost effective light source to the ultra-broadband time-resolved coherent anti-Stokes Raman scattering spectroscopy.
基金Supported by the National Natural Science Foundation of China (61008036)China Postdoctoral Science Foundation(20110490779)
文摘Metal-dielectric subwavelength gratings under s-polarized and p-polarized visible radiation are studied for discovering their intriguing behaviors of spectral resonance and color property.The dependence of their resonance and color on grating parameters as well as angle of incidence and position of plane of incidence is also analyzed.For s-polarized light,the behavior of spectral resonance with single peak and higher peak efficiency is found.While transmission spectra for p-polarized light are not able to achieve a behavior like that of s-polarization,creating a perceived color is feasible.Moreover,a security grating with distinctive color shifts has been designed and its resonant properties as well as related color variation have also been provided.
基金We appreciate the financial support from the National Key Research and Development Program of China(2017YFB1300300)the National Natural Science Foundation of China(62122059,81925020,61976152,and 81630051)the Young Elite Scientist Sponsorship Program by CAST(2018QNRC001).
文摘It has been almost 50 years since the term“brain–computer interface”(BCI)was first proposed by Jacques J.Vidal in 1973[1].Unlike traditional electronic interfaces that transmit nonliving information between devices,BCIs set up a communication bridge between a living brain and nonliving devices.Technically speaking,a BCI is a system that measures brain activity and converts it into the artificial outputs that replace,restore,enhance,supplement,or improve the natural central nervous system outputs[2].At present,electroencephalography(EEG)is the most commonly used brain signal for BCIs.
文摘Passively Q-switched quasi-continuous-wave (QCW) diode-pumped Nd:YAG laser with Cr^4+ :YAG as saturable absorber is numerically investigated by solving the coupled rate equations. The threshold pump rate for passively Q-switched QCW-pumped laser is derived. The effects of the pump rate and pump-pulse duration on the laser operation characteristics are studied theoretically. The pump power range can be estimated according to the number of output pulses. The numerical simulation results are in good agreement with the experimental results.
基金Supported by the National Basic Research Programme of China under Grant No 2006CB806000, the National Natural Science Foundation of China under Grant Nos 60490280 and 60578007, NSFC-JSPS International Cooperation Programme under Grant No 60611140297, the Tianjin Natural Science Foundation under Grant No 07JCYBJC15500.
文摘We propose a novel technique for generating intense few to mono-cycle femtosecond pulses. The simulation demonstrate that for the temperature difference of 300K, the spectrum of the output pulses is increased by 67% and the transform limited pulse width is reduced almost by half, compared with those obtained with hollow fibres in uniform temperature.
文摘A compact, efficient and high-power laser diode (LD) single-end-pumped Nd:YVO4 laser with continuous-wave emission at 1342 nm is reported. With a single crystal single-end-pumped by fibre-coupled LD array, an output power of 7.36W is obtained from the laser cavity of concave-convex shape, corresponding to an optical-to-optical efficiency of 32.8%. The laser is operated in TEM00 mode with small rms amplitude noise of 0.3%. The influences of the Nd concentration, transmissivity of the output mirror and the cavity length on the output power have been studied experimentally.
基金the National Natural Science Foundation of China (Grant Nos.81401453,81371602,61475115,61475116,61575140,81571723,and 81671728)the Tianjin Municipal Government of China (Grant Nos.14JCQNJC14400,15JCZDJC31800,15JCQNJC14500,and 16JCZDJC31200)
文摘Photoacoustic mesoscopy(PAMe) offers high-sensitivity in vivo imaging based on the rich optical contrast in biological tissues,with sub-100-micron resolutions at a few millimeters depth. By benefiting from low ultrasonic scattering,this emerging technology has pushed the penetration depth beyond the optical diffuse limit unprecedented for high-resolution optical methods.Here,we review ed the state-of-art implementations of PAMe and their achievements in biological and primary clinical applications. With the high-frequency focused ultrasonic detector,the high-resolution optical visualization can be achieved by utilizing various PAMe systems. These capabilities of PAMe have made it well applicable for understanding the biological mechanisms,exploring the pathological features and analyzing the characteristics of human skin. Future improvements and prospects of PAMe are also mentioned,suggesting its great potential tow ards the corresponding emerging biomedical and clinical applications.
基金supported by the National Natural Science Foundation of China (Grant No. 10974063)the Natural Science Foundation of Hubei Province of China (Grant No. 2010CDA001)+2 种基金Ph. D. Program Foundation of the Ministry of Education of China (Grant No. 20100142110042)the Fundamental Research Funds for the Central Universities (Grant No. HUST:2010MS041)the National "973" Project (Grant No. 2007CB310403)
文摘This paper presents a set of equations describing the terahertz generation and electro-optic detection based on optical rectification in zincblende crystals. The dependence of terahertz emission efficiency on the polarization of incident beam and crystal-orientation is discussed. For the experimental setup with a transceiver which transmits and detects terahertz radiation in the same crystal, we have demonstrated the optimal combination of both parameters above to optimize the working efficiency. Equations supplied in this paper are valid for zincblende crystals with arbitrary crystal- orientation and every possible polarization of an incident beam, which are of great significance for the optimization of a system.
基金from National Natural Science Foundation of China(NSFC)81571719,61322502Open Project of State Key Laboratory of Modern Optical Instrumentation,Zhejiang University,and Program for Changjiang Scholars and Innovative Research Team in Uni-versity IRT13033.
文摘Usually,only focused femtosecond(fs)lasers at near-infrared(NIR)range can induce photo-damage to transparent cells,making it difficult to treat large amount of cells by such optical methods for photostimulation.In this study,we clarify the mechanism of photodamage to cells that are co-cultured with gold nanorods(GNRs)by fs laser.The pulse duration and repetition rate of the fs laser play a key role in cell damage suggesting that the heat accumulation con-tributes to the major part for the cell damage rather than the high peak power which mainly determines the efficiency of multiphoton excitation.We further show that cellular Ca^(2+)can also be released in this scheme,but the process is more sensitive to peak power.Our results can provide a large-scale GNR-mediated photostimulation for cell signaling modulation.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10904079 and 60838001)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20090031120041)the Natural Science Foundation of Tianjin (Grant No. 10JCYBJC01300)
文摘This paper numerically simulates the process of ablation of an aluminum target by an intense femtosecond laser with a fluence of 40 J/cm2 based on the two-temperature equation, and obtains the evolution of the free electron temperature and lattice temperature over a large temporal and depth range, for the first time. By investigating the temporal evolution curves of the free electron temperature and lattice temperature at three representative depths of 0, 100 nm and 500 nm, it reveals different characteristics and mechanisms of the free electron temperature evolution at different depths. The results show that, in the intense femtosecond laser ablation of aluminum, the material ablation is mainly induced by the thermal conduction of free electrons, instead of the direct absorption of the laser energy; in addition, the thermal conduction of free electrons and the coupling effect between electrons and lattice will induce the temperature of free electrons deep inside the target to experience a process from increase to decrease and finally to increase again.
基金the National Natural Science Foundation of China(Grant No.81272495)the Natural Science Foundation of Tianjin(Grant No.16JC2DJC32200)。
文摘The hemispherical phased transducer maximizes the coverage of the skull and the ultrasonic energy per unit area of the skull is minimized,thereby reducing the risk of skull burns,but the transducer has a small focal area adjustment range,increasing the focal length of treatment is an urgent question for this type of transducer.In this paper,a three-dimensional high-intensity focused ultrasound(HIFU)transcranial propagation model is established based on the human head structure.The finite difference time domain(FDTD)is combined with the Westervelt acoustic wave nonlinear propagation equation and Penne's biological heat conduction equation for numerical simulation of the sound pressure field and temperature field.Forming a treatable focal area in a small-opening hemispherical transducer with a small amount of numerical simulation calculation focusing at a set position to determine the minimum partial excitation area ratio of focusing.And then,applying these preliminary results to a large-opening diameter hemispherical transducer and the temperature field formed by it or full excitation is studied.The results show that the focus area with the excitation area ratio of less than 22%moves forward to the transducer side when the excitation sound is formed.When the excitation area ratio is greater than or equal to 23%,it focuses at the set position.In the case of partial incentives,using 23%of the partial array,the adjustable range of the treatable focal area formed in the three-dimensional space is larger than that of the full excitation.
文摘The well-known Fraunhofer multi-slit diffraction is described as the multi-slit interference modulated by the singleslit diffraction, namely the multiplication between the single-slit diffraction factor and the multi-slit interference factor. By considering the simplified argument we show that the multi-slit diffraction of evanescent waves which are in the near-field region also has the interference and diffraction effects, and that this two-fold effect can be expressed as the convolution of the diffraction factor and the interference factor. Our conclusion could be helpful to understand the contribution of evanescent waves to the optical responses of sub-wavelength structures such as slits and grooves.