We investigate the effects of spontaneously generated coherence （SGC） on both the steady and transient gain properties in a four-level inverted-Y-type atomic system in the presence of a weak probe, two strong cohere...We investigate the effects of spontaneously generated coherence （SGC） on both the steady and transient gain properties in a four-level inverted-Y-type atomic system in the presence of a weak probe, two strong coherent fields, and an incoherent pump. For the steady process, we find that the inversionless gain mainly origins from SGC. In particular, we can modulate the inversionless gain by changing the relative phase between the two fields. Moreover, the amplitude of the gain peak can be enhanced and the additional gain peak can appear by changing the detuning of the coupling field. As for the transient process, the transient gain properties can also be dramatically affected by the SGC. Compared to the case without SGC, the transient gain can be greatly enhanced with completely eliminated transient absorption by choosing the proper relative phase between the two fields. And the inverted-Y-type system with SGC can be simulated in both atomic and semiconductor quantum well systems avoiding the conditions of SGC.展开更多
Stable dark soliton and dark pulse formation in normally dispersive and red-detuned microcavities are investigated by numerically solving the normalized Lugiato-Lefever equation. The soliton essence is proved by fitti...Stable dark soliton and dark pulse formation in normally dispersive and red-detuned microcavities are investigated by numerically solving the normalized Lugiato-Lefever equation. The soliton essence is proved by fitting the calculated field intensity profile with the analytical formula of a dark soliton. Meanwhile, we find that a dark soliton can be generated either from the nonlinear evolution of an optical shock wave or narrowing of a locally broad dark pulse with smoother fronts. Explicit analytical expression is obtained to describe the oscillatory fronts of the optical shock wave. Furthermore,from the calculation results, we show that for smaller frequency detunings, e.g., α 3, in addition to the dark soliton formation, a single dark pulse with an oscillatory dip can also arise and propagate stably in the microcavity under proper pump detuning and pump strength combination. The existence region together with various field intensity profiles and the corresponding spectra of single dark pulse are demonstrated.展开更多
Exact solutions of Maxwell＇s equations describing the lightwave through 3-layer-structured cylindrical waveguide are obtained and the mode field diameter and nonlinear coefficient of air-core nanowires （ACNWs） are ...Exact solutions of Maxwell＇s equations describing the lightwave through 3-layer-structured cylindrical waveguide are obtained and the mode field diameter and nonlinear coefficient of air-core nanowires （ACNWs） are numerically calculated. The simulation results show that ACNWs offer some unique optical properties, such as tight field confining ability and extremely high nonlinearity. At a certain wavelength and air core radius, we optimize the waveguide design to maximize the nonlinear coefficient and minimize the mode field diameter. Our results show that the ACNWs may be powerful potential tools for novel micro-photonic devices in the near future.展开更多
Digital in-line holographic microscopy(DIHM)is a widely used interference technique for real-time reconstruction of living cells’morphological information with large space-bandwidth product and compact setup.However,...Digital in-line holographic microscopy(DIHM)is a widely used interference technique for real-time reconstruction of living cells’morphological information with large space-bandwidth product and compact setup.However,the need for a larger pixel size of detector to improve imaging photosensitivity,field-of-view,and signal-to-noise ratio often leads to the loss of sub-pixel information and limited pixel resolution.Additionally,the twin-image appearing in the reconstruction severely degrades the quality of the reconstructed image.The deep learning(DL)approach has emerged as a powerful tool for phase retrieval in DIHM,effectively addressing these challenges.However,most DL-based strategies are datadriven or end-to-end net approaches,suffering from excessive data dependency and limited generalization ability.Herein,a novel multi-prior physics-enhanced neural network with pixel super-resolution(MPPN-PSR)for phase retrieval of DIHM is proposed.It encapsulates the physical model prior,sparsity prior and deep image prior in an untrained deep neural network.The effectiveness and feasibility of MPPN-PSR are demonstrated by comparing it with other traditional and learning-based phase retrieval methods.With the capabilities of pixel super-resolution,twin-image elimination and high-throughput jointly from a single-shot intensity measurement,the proposed DIHM approach is expected to be widely adopted in biomedical workflow and industrial measurement.展开更多
The angle compensation method is adopted to detect sloshing waves by laser diffraction, in the case that the wavelength of the sloshing waves is much greater than that of the incident light. The clear diffraction patt...The angle compensation method is adopted to detect sloshing waves by laser diffraction, in the case that the wavelength of the sloshing waves is much greater than that of the incident light. The clear diffraction pattern is observed to be of asymmetry, involving orders, position and interval of the diffraction spots that are discovered during the light grazing incidence. It is found that the larger the angle of incidence is, the more obvious the asymmetry is. The higher the negative diffraction orders are, the smaller the intervals between spots are. On the contrary~ in the positive region, the higher the diffraction orders are, the larger the spot intervals are. The positive interval is larger than that of the same negative diffraction order. If the incident angle reaches 1.558 rad in the experiment, all positive diffraction orders completely vanish. Based on the mechanism of phase modulation and with the Fourier transform method, the relations between the incident angle and position, interval spaces, and orders of diffraction spots are derived theoretically. The theoretical calculations are compared with the experimental data, and the comparison shows that the theoretical calculations are in good agreement with the experimental measurement.展开更多
The structures of pseudo-binary GeS2-Sb2S3, GeS2-CdS, Sb2S3-CdS, and pseudo-ternary GeS2-Sb2S3-CdS chalco- genide systems are systematically investigated by Raman spectroscopy. It is shown that a small number of [S3Ge...The structures of pseudo-binary GeS2-Sb2S3, GeS2-CdS, Sb2S3-CdS, and pseudo-ternary GeS2-Sb2S3-CdS chalco- genide systems are systematically investigated by Raman spectroscopy. It is shown that a small number of [S3Ge-GeS3] structural units （SUs） and -S-S-/S8 groups exist simultaneously in GeS2 glass which has a three-dimensional continuous network backbone consisting of cross-linked corner-sharing and edge-sharing [GeS4] tetrahedra. When Sb2S3 is added into GeS2 glass, the network backbone becomes interconnected [GeS4] tetrahedra and [SbS3] pyramids. Moreover, Ge atoms in [S3Ge-GeS3] SUs tend to capture S atoms from Sb2S3, leading to the formation of [S2Sb-SbS2] SUs. When CdS is added into GeS2 glass, [Cd4GeS6] polyhedra are formed, resulting in a strong crystallization tendency. In addition, Ge atoms in [S3Ge-GeS3] SUs tend to capture S atoms from CdS, resulting in the dissolution of Ge-Ge bond. Co-melting of Sb2S3 or CdS with GeS2 reduces the viscosity of the melt and improves the homogeneity of the glass. The GeS2 glass can only dissolve up to 10-mol% CdS without crystallization. In comparison, GeS2-SbzS3 glasses can dissolve up to 20-mo1% CdS, implying that Sb2S3 could delay the construction of [Cd4GeS6] polyhedron and increase the dissolving amount of CdS in the glass.展开更多
A highly reliable interface of self-aligned barrier CuSiN thin layer between the Cu film and the nano-porous SiC：H （p-SiC：H） capping barrier （k=3.3） has been developed in the present work. With the introduction ...A highly reliable interface of self-aligned barrier CuSiN thin layer between the Cu film and the nano-porous SiC：H （p-SiC：H） capping barrier （k=3.3） has been developed in the present work. With the introduction of self-aligned barrier （SAB） CuSiN between a Cu film and a p-SiC：H capping barrier, the interfacial thermal stability and the adhesion of the Cu/p-SiC：H film are considerably enhanced. A significant improvement of adhesion strength and thermal stability of Cu/p-SiC：H/SiOC：H film stack has been achieved by optimizing the pre-clean step before caplayer deposition and by forming the CuSiN-like phase. This cap layer on the surface of the Cu can provide a more cohesive interface and effectively suppress Cu atom migration as well.展开更多
A Nd：CLNGG waveguide structure operated at wavelengths of both 632.8 nm and 1539 nm was demonstrated for the first time to our knowledge, which was produced by the 480-keV H＋ ion implantation with a dose of 1.0×...A Nd：CLNGG waveguide structure operated at wavelengths of both 632.8 nm and 1539 nm was demonstrated for the first time to our knowledge, which was produced by the 480-keV H＋ ion implantation with a dose of 1.0× 10^17 protons/cm2, Its propagating modes at 632.8 nm and 1539 nm were measured by the well-known prism coupling technique. The refractive index profile at either 632.8-nm wavelength or 1539-nm wavelength was optical barrier type in the proton-implanted Nd：CLNGG crystal optical waveguide, which was calculated by using the reflectivity calculation method. The near-field light intensity distributions were also simulated by the finite-difference beam propagation method in the visible and nearinfrared bands.展开更多
Molecular-frame photoelectron momentum distributions(MF-PMDs) of an H_(2)^(+) molecule ion in the presence of a pair of counter-rotating circularly polarized attosecond extreme ultraviolet laser pulses is studied by n...Molecular-frame photoelectron momentum distributions(MF-PMDs) of an H_(2)^(+) molecule ion in the presence of a pair of counter-rotating circularly polarized attosecond extreme ultraviolet laser pulses is studied by numerically solving the two-dimensional time-dependent Schrodinger equation within the frozen-nuclei approximation. At small time delay, our simulations show that the electron vortex structure is sensitive to the time delay and relative phase between the counterrotating pulses when they are partially overlapped. By adjusting time delay and relative phase, we have the ability to manipulate the MF-PMDs and the appearance of spiral arms. We further show that the internuclear distance can affect the spiral vortices due to its different transition cross sections in the parallel and perpendicular geometries. The lowest-order perturbation theory is employed to interpret these phenomena qualitatively. It is concluded that the internuclear distancedependent transition cross sections and the confinement effect in diatomic molecules are responsible for the variation of vortex structures in the MF-PMDs.展开更多
Metasurfaces,with extremely exotic capabilities to manipulate electromagnetic(EM)waves,have derived a plethora of advanced metadevices with intriguing functionalities.Tremendous endeavors have been mainly devoted to t...Metasurfaces,with extremely exotic capabilities to manipulate electromagnetic(EM)waves,have derived a plethora of advanced metadevices with intriguing functionalities.Tremendous endeavors have been mainly devoted to the static metasurfaces and metadevices,where the functionalities cannot be actively tuned in situ post-fabrication.Due to the in-trinsic advantage of active tunability by external stimulus,graphene has been successively demonstrated as a favorable candidate to empower metasurfaces with remarkably dynamic tunability,and their recent advances are propelling the EM wave manipulations to a new height:from static to dynamic.Here,we review the recent progress on dynamic metasur-faces and metadevices enabled by graphene with the focus on electrically-controlled dynamic manipulation of the EM waves covering the mid-infrared,terahertz,and microwave regimes.The fundamentals of graphene,including basic ma-terial properties and plasmons,are first discussed.Then,graphene-empowered dynamic metasurfaces and met-adevices are divided into two categories,i.e.,metasurfaces with building blocks of structured graphene and hybrid metasurfaces integrated with graphene,and their recent advances in dynamic spectrum manipulation,wavefront shap-ing,polarization control,and frequency conversion in near/far fields and global/local ways are elaborated.In the end,we summarize the progress,outline the remaining challenges,and prospect the potential future developments.展开更多
In this paper, polarization properties and propagation characteristics of polymer photonic crystal fibres with elliptical core and non-hexagonal symmetry structure are investigated by using the full vectorial plane wa...In this paper, polarization properties and propagation characteristics of polymer photonic crystal fibres with elliptical core and non-hexagonal symmetry structure are investigated by using the full vectorial plane wave method. The results show that the birefringence of the fibre is induced by asymmetries of both the cladding and the core. Moreover, by adjusting the non-symmetrical ratio factor of cladding η from 0.4 to 1 in step 0.1, we find the optimized design parameters of the fibre with high birefringence and limited polarization mode dispersion, operating in a single mode regime at an appropriate wavelength range. The range of wavelength approaches the visible and near-infrared which is consistent with the communication windows of polymer optical fibres.展开更多
This paper investigates the temporal behaviour of open-circuit bright photovoltaic spatial solitons by using numerical techniques. It shows that when the intensity ratio of the soliton, the ratio between the soliton p...This paper investigates the temporal behaviour of open-circuit bright photovoltaic spatial solitons by using numerical techniques. It shows that when the intensity ratio of the soliton, the ratio between the soliton peak intensity and the dark irradiance, is small, the quasi-steady-state soliton width decreases monotonically with the increase of τ-, where τ- is the parameter correlated with the time, that when the intensity ratio of the soliton is big, the quasi-steady-state soliton width decreases with the increase of τ- and then increases with τ, and that the formation time of the steady-state solitons is not correlated with the intensity ratio of the soliton. It finds that the local nonlinear effect increases with the photovoltaic field, which behaves as that the width of soliton beams is small and the self-focusing quasi-period is short. On the other hand, we also discuss that both the time and the temperature have an effect on the beam bending.展开更多
A new prototype of single photon imaging system based on wedge and strip anodes is developed. The prototype can directly measure the intensity and position information for an ultra-weak radiant source which takes on t...A new prototype of single photon imaging system based on wedge and strip anodes is developed. The prototype can directly measure the intensity and position information for an ultra-weak radiant source which takes on the character of single photons. The image of the ultra-weak radiant source can be reconstructed with a wedge and strip anodes detector and an electronic readout subsystem by photon counting and photon position sensitive detecting in a period of time. With proper evaluation, the prototype reveals a spatial resolution superior to 150μm, a 66-kHz maximal counting rate and a dark-count below 0.67 count /cm^2 s.展开更多
Interdigitated finger capacitance of a continuous-wave terahertz photomixer is calculated using the finite element method.For the frequently used electrode width（0.2 μm） and gap width（1.8 μm）,the finger capacita...Interdigitated finger capacitance of a continuous-wave terahertz photomixer is calculated using the finite element method.For the frequently used electrode width（0.2 μm） and gap width（1.8 μm）,the finger capacitance increases quasi-quadratically with the number of electrodes increasing.The quasi-quadratic dependence can be explained by a sequence of lumped capacitors connected in parallel.For a photomixer composed of 10 electrodes and 9 photoconductive gaps,the finger capacitance increases as the gap width increases at a small electrode width,and follows the reverse trend at a large electrode width.For a constant electrode width,the finger capacitance first decreases and then slightly increases as the gap broadens until the smallest finger capacitance is formed.We also investigate the finger capacitances at different electrode and gap configurations with the 8 μm × 8 μm photomixer commonly used in previous studies.These calculations lead to a better understanding of the finger capacitance affected by the finger parameters,and should lead to terahertz photomixer optimization.展开更多
We propose a novel all-optical format conversion from the return-to-zero （RZ） to the non-return-to-zero （NRZ） based on single semiconductor optical amplifier （SOA） and optical band-pass filter （OBE）. We demons...We propose a novel all-optical format conversion from the return-to-zero （RZ） to the non-return-to-zero （NRZ） based on single semiconductor optical amplifier （SOA） and optical band-pass filter （OBE）. We demonstrate the proof of the principle experiment at 10 Gbps by using the test SOA and OBF converter. The format conversion can be achieved with output extinction ratio of 11.51 dB. The BER is 5.5×10^-9 when the power of NRZ is - 10 dBm. The proposed scheme is robust and potential for applications in optical networks.展开更多
The optical absorption of GaAs nanorings （NRs） under adc electric field and a terahertz （THz） ac electric field applied in the plane containing the NRs is investigated theoretically. The NRs may enclose some magne...The optical absorption of GaAs nanorings （NRs） under adc electric field and a terahertz （THz） ac electric field applied in the plane containing the NRs is investigated theoretically. The NRs may enclose some magnetic flux in the presence of a magnetic field perpendicular to the NRs plane. Numerical calculation shows that the excitonic effects are essential to correctly describe the optical absorption in NRs. The applied lateral THz electric field, as well as the dc field leads to reduction, broadening and splitting of the exciton peak. In contrast to the presence of a dc field, significant optical absorption peak arises below the zero-field bandgap in the presence ofa THz electric field at a certain frequency. The optical absorption spectrum depends evidently on the frequency and amplitude of the applied THz field and on the magnetic flux threading the NRs. This promises potential applications of NRs for magneto-optical and THz electro-optical sensing.展开更多
Two coupled paralnetric four-wave-mixing processes in Rb atoms are studied using perturbation theory, which reveals clear evidence of tile appearance of quantum beat at 608cm^-1, corresponding to the energy difference...Two coupled paralnetric four-wave-mixing processes in Rb atoms are studied using perturbation theory, which reveals clear evidence of tile appearance of quantum beat at 608cm^-1, corresponding to the energy difference of the 7s - 5d states of Rb atoms, in the parametric four-wave-mixing signals. A pump-probe technique is utilized to observe the quantum beat. Tinle-varying characteristics of the quantum beat are investigated using time-dependellt Fourier transform. The results show that the time-varying characteistics of the quantum beat not oldy offers a sensitive detecting method for observing the decay of atomic wave packets, but also provides a potential tool for monitoriHg the dissociation of molecules.展开更多
We have performed a full numerical calculation of the Franz-Keldysh （FK） effect on magnetoexcitons in a bulk GaAs semiconductor. By employing an initial wlue method in combination with the application of a perfect m...We have performed a full numerical calculation of the Franz-Keldysh （FK） effect on magnetoexcitons in a bulk GaAs semiconductor. By employing an initial wlue method in combination with the application of a perfect matched layer, the numerical effort and storage size are dramatically reduced due to a significant reduction in both computed domain and number of base functions. In the absence of an electric field, the higher magnetoexcitonic peaks show distinct Fano lineshape due to the degeneracy with continuum states of the lower Landau levels. The magnetoexcitons that belong to the zeroth Landau level remain in bound states and lead to Lorentzian lineshape, because they are not degenerated with continuum states. In the presence of an electric field, the FK effect on each magnetoexcitonic resonance can be identified for high magnetic fields. However, for low magnetic fields, the FK oscillations dominate the spectrum structure in the vicinity of the bandgap edge and the magnetoexcitonic resonances dominate the spectrum structure of higher energies. In the moderate electric fields, the interplay of FK effect and magnetoexcitonic resonance leads to a complex and rich structure in the absorption spectrum.展开更多
Optical emission spectra of the plasma generated by a 532 nm Nd：YAG laser irra- diation onto a standard aluminum alloy （E414d） was recorded and analyzed. The electron tem- perature was determined using the Boltzman...Optical emission spectra of the plasma generated by a 532 nm Nd：YAG laser irra- diation onto a standard aluminum alloy （E414d） was recorded and analyzed. The electron tem- perature was determined using the Boltzmann plot method with three aluminum spectral lines at 236.71 nm, 257.509 nm and 308.215 nm, whereas the electron density was inferred by measuring the Stark broadening line profile of Al（II） 281.619 nm. The experimental results confirmed that the local thermodynamic equilibrium was valid and the plasma was optically thin. The spectral line intensity increased initially with the increase in laser irradiance and saturated at higher Jr- radiance levels. Results showed that the energy losses due to the reflection of laser beam from the plasma itself were insignificant. The absorption in the plasma through inverse bremsstrahlung and two-photon ionization were studied. At the same timer the variation of transition probability ratio of Al（I） 309.28 nm to Al（I） 308.21 nm with laser power density was also studied.展开更多
With the rapid demand for underwater optical communication(UOC), studies of UOC degradation by oceanic turbulence have attached increasing attention worldwide and become a research hot-spot in recent years. Previous s...With the rapid demand for underwater optical communication(UOC), studies of UOC degradation by oceanic turbulence have attached increasing attention worldwide and become a research hot-spot in recent years. Previous studies used a simplified and inaccurate oceanic turbulence spectrum, in which the eddy diffusivity ratio between temperature and salinity is assumed to be unity and the outer scale of turbulence is assumed to be infinite. However, both assumptions are not true in most of the actual marine environments. In this paper, based on the Rytov theory in weak turbulence, we derive analytical expressions of "the aperture-averaged scintillation index"(SI) for both plane and spherical waves, which can clearly demonstrate how SI is influenced by several key factors in UOC. Then, typical fade statistics of the UOC system in weak turbulence is discussed including the probability of fade, the expected number of fades per time, the mean fade time,signal-to-noise ratio and bit error rate. Our results show that spherical wave is preferable in the UOC system in weak turbulence compared to plane wave, and the aperture-averaged effect has a significant impact on UOC system's performance.Our results can be used to determine those key parameters for designing the UOC system over reasonable ranges.展开更多
基金Project supported by the National Basic Research Program of China(Grant Nos.2011CB921603 and 2013CB933300)the National Natural Science Foundation of China(Grant Nos.11304308,61076064,and 61176046)+1 种基金Natural Science Foundation of Jilin Province,China(Grant Nos.20140101203JC)the Hundred Talents Program of the Chinese Academy of Sciences
文摘We investigate the effects of spontaneously generated coherence （SGC） on both the steady and transient gain properties in a four-level inverted-Y-type atomic system in the presence of a weak probe, two strong coherent fields, and an incoherent pump. For the steady process, we find that the inversionless gain mainly origins from SGC. In particular, we can modulate the inversionless gain by changing the relative phase between the two fields. Moreover, the amplitude of the gain peak can be enhanced and the additional gain peak can appear by changing the detuning of the coupling field. As for the transient process, the transient gain properties can also be dramatically affected by the SGC. Compared to the case without SGC, the transient gain can be greatly enhanced with completely eliminated transient absorption by choosing the proper relative phase between the two fields. And the inverted-Y-type system with SGC can be simulated in both atomic and semiconductor quantum well systems avoiding the conditions of SGC.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFF0200702)the National Natural Science Foundation of China(Grant Nos.61690222 and 11573058)the CAS-SAFEA International Partnership Program for Creative Research Teams
文摘Stable dark soliton and dark pulse formation in normally dispersive and red-detuned microcavities are investigated by numerically solving the normalized Lugiato-Lefever equation. The soliton essence is proved by fitting the calculated field intensity profile with the analytical formula of a dark soliton. Meanwhile, we find that a dark soliton can be generated either from the nonlinear evolution of an optical shock wave or narrowing of a locally broad dark pulse with smoother fronts. Explicit analytical expression is obtained to describe the oscillatory fronts of the optical shock wave. Furthermore,from the calculation results, we show that for smaller frequency detunings, e.g., α 3, in addition to the dark soliton formation, a single dark pulse with an oscillatory dip can also arise and propagate stably in the microcavity under proper pump detuning and pump strength combination. The existence region together with various field intensity profiles and the corresponding spectra of single dark pulse are demonstrated.
基金supported by the "Hundreds of Talents Programs" of the Chinese Academy of Sciencesby the National Natural Science Foundation of China (Grant Nos 10874239,10604066 and 60537060)
文摘Exact solutions of Maxwell＇s equations describing the lightwave through 3-layer-structured cylindrical waveguide are obtained and the mode field diameter and nonlinear coefficient of air-core nanowires （ACNWs） are numerically calculated. The simulation results show that ACNWs offer some unique optical properties, such as tight field confining ability and extremely high nonlinearity. At a certain wavelength and air core radius, we optimize the waveguide design to maximize the nonlinear coefficient and minimize the mode field diameter. Our results show that the ACNWs may be powerful potential tools for novel micro-photonic devices in the near future.
基金National Natural Science Foundation of China (62275267, 62335018, 12127805, 62105359)National Key Research and Development Program of China (2021YFF0700303, 2022YFE0100700)Youth Innovation Promotion Association, CAS (2021401)
文摘Digital in-line holographic microscopy(DIHM)is a widely used interference technique for real-time reconstruction of living cells’morphological information with large space-bandwidth product and compact setup.However,the need for a larger pixel size of detector to improve imaging photosensitivity,field-of-view,and signal-to-noise ratio often leads to the loss of sub-pixel information and limited pixel resolution.Additionally,the twin-image appearing in the reconstruction severely degrades the quality of the reconstructed image.The deep learning(DL)approach has emerged as a powerful tool for phase retrieval in DIHM,effectively addressing these challenges.However,most DL-based strategies are datadriven or end-to-end net approaches,suffering from excessive data dependency and limited generalization ability.Herein,a novel multi-prior physics-enhanced neural network with pixel super-resolution(MPPN-PSR)for phase retrieval of DIHM is proposed.It encapsulates the physical model prior,sparsity prior and deep image prior in an untrained deep neural network.The effectiveness and feasibility of MPPN-PSR are demonstrated by comparing it with other traditional and learning-based phase retrieval methods.With the capabilities of pixel super-resolution,twin-image elimination and high-throughput jointly from a single-shot intensity measurement,the proposed DIHM approach is expected to be widely adopted in biomedical workflow and industrial measurement.
基金Supported by the Open Research Fund of State Key Laboratory of Transient Optics and Photonics of Chinese Academy of Sciences under Grant No SKLST201508the China Postdoctoral Science Foundation Funded Project under Grant No 2015M580945the Government of Chaoyang District Postdoctoral Research Foundation
文摘The angle compensation method is adopted to detect sloshing waves by laser diffraction, in the case that the wavelength of the sloshing waves is much greater than that of the incident light. The clear diffraction pattern is observed to be of asymmetry, involving orders, position and interval of the diffraction spots that are discovered during the light grazing incidence. It is found that the larger the angle of incidence is, the more obvious the asymmetry is. The higher the negative diffraction orders are, the smaller the intervals between spots are. On the contrary~ in the positive region, the higher the diffraction orders are, the larger the spot intervals are. The positive interval is larger than that of the same negative diffraction order. If the incident angle reaches 1.558 rad in the experiment, all positive diffraction orders completely vanish. Based on the mechanism of phase modulation and with the Fourier transform method, the relations between the incident angle and position, interval spaces, and orders of diffraction spots are derived theoretically. The theoretical calculations are compared with the experimental data, and the comparison shows that the theoretical calculations are in good agreement with the experimental measurement.
基金supported by the National Natural Science Foundation of China(Grant Nos.61475189,61405240,and 61575086)the Natural Science Basic Research Project in Shaanxi Province,China(Grant No.2015JQ5141)the Jiangsu Key Laboratory of Advanced Laser Materials and Devices,Jiangsu Normal University,China(Grant No.KLALMD-2015-08)
文摘The structures of pseudo-binary GeS2-Sb2S3, GeS2-CdS, Sb2S3-CdS, and pseudo-ternary GeS2-Sb2S3-CdS chalco- genide systems are systematically investigated by Raman spectroscopy. It is shown that a small number of [S3Ge-GeS3] structural units （SUs） and -S-S-/S8 groups exist simultaneously in GeS2 glass which has a three-dimensional continuous network backbone consisting of cross-linked corner-sharing and edge-sharing [GeS4] tetrahedra. When Sb2S3 is added into GeS2 glass, the network backbone becomes interconnected [GeS4] tetrahedra and [SbS3] pyramids. Moreover, Ge atoms in [S3Ge-GeS3] SUs tend to capture S atoms from Sb2S3, leading to the formation of [S2Sb-SbS2] SUs. When CdS is added into GeS2 glass, [Cd4GeS6] polyhedra are formed, resulting in a strong crystallization tendency. In addition, Ge atoms in [S3Ge-GeS3] SUs tend to capture S atoms from CdS, resulting in the dissolution of Ge-Ge bond. Co-melting of Sb2S3 or CdS with GeS2 reduces the viscosity of the melt and improves the homogeneity of the glass. The GeS2 glass can only dissolve up to 10-mol% CdS without crystallization. In comparison, GeS2-SbzS3 glasses can dissolve up to 20-mo1% CdS, implying that Sb2S3 could delay the construction of [Cd4GeS6] polyhedron and increase the dissolving amount of CdS in the glass.
基金supported by the National Natural Science Foundation of China(Nos.11075112,61040034)Specialized Research Fund for the Doctoral Program of Higher Education(New Teachers,No.20100181120112)
文摘A highly reliable interface of self-aligned barrier CuSiN thin layer between the Cu film and the nano-porous SiC：H （p-SiC：H） capping barrier （k=3.3） has been developed in the present work. With the introduction of self-aligned barrier （SAB） CuSiN between a Cu film and a p-SiC：H capping barrier, the interfacial thermal stability and the adhesion of the Cu/p-SiC：H film are considerably enhanced. A significant improvement of adhesion strength and thermal stability of Cu/p-SiC：H/SiOC：H film stack has been achieved by optimizing the pre-clean step before caplayer deposition and by forming the CuSiN-like phase. This cap layer on the surface of the Cu can provide a more cohesive interface and effectively suppress Cu atom migration as well.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11405041 and 61177084)the Nanjing University of Posts and Telecommunications Scientific Foundation(NUPTSF),China(Grant No.NY214159)the RCOCET,China(Grant No.ZSF0401)
文摘A Nd：CLNGG waveguide structure operated at wavelengths of both 632.8 nm and 1539 nm was demonstrated for the first time to our knowledge, which was produced by the 480-keV H＋ ion implantation with a dose of 1.0× 10^17 protons/cm2, Its propagating modes at 632.8 nm and 1539 nm were measured by the well-known prism coupling technique. The refractive index profile at either 632.8-nm wavelength or 1539-nm wavelength was optical barrier type in the proton-implanted Nd：CLNGG crystal optical waveguide, which was calculated by using the reflectivity calculation method. The near-field light intensity distributions were also simulated by the finite-difference beam propagation method in the visible and nearinfrared bands.
基金Project supported by the Natural Science Foundation of Jilin Province,China (Grant No.20220101016JC)the National Key Research and Development Program of China (Grant No.2022YFE0134200)+1 种基金the National Natural Science Foundation of China (Grant Nos.12174147,91850114,and 11774131)the Open Research Fund of State Key Laboratory of Transient Optics and Photonics。
文摘Molecular-frame photoelectron momentum distributions(MF-PMDs) of an H_(2)^(+) molecule ion in the presence of a pair of counter-rotating circularly polarized attosecond extreme ultraviolet laser pulses is studied by numerically solving the two-dimensional time-dependent Schrodinger equation within the frozen-nuclei approximation. At small time delay, our simulations show that the electron vortex structure is sensitive to the time delay and relative phase between the counterrotating pulses when they are partially overlapped. By adjusting time delay and relative phase, we have the ability to manipulate the MF-PMDs and the appearance of spiral arms. We further show that the internuclear distance can affect the spiral vortices due to its different transition cross sections in the parallel and perpendicular geometries. The lowest-order perturbation theory is employed to interpret these phenomena qualitatively. It is concluded that the internuclear distancedependent transition cross sections and the confinement effect in diatomic molecules are responsible for the variation of vortex structures in the MF-PMDs.
基金supported by the National Key R&D Program of China (2017YFA0303800)the National Natural Science Foundation of China (61805277, 11634010, 91950207, 11974283, 11774290)+1 种基金the Fundamental Research Funds for the Central Universities (3102017AX009, 3102019PY002, 3102019JC008)the Natural Science Basic Research Program of Shaanxi (2019JQ-447, 2020JM-130)
文摘Metasurfaces,with extremely exotic capabilities to manipulate electromagnetic(EM)waves,have derived a plethora of advanced metadevices with intriguing functionalities.Tremendous endeavors have been mainly devoted to the static metasurfaces and metadevices,where the functionalities cannot be actively tuned in situ post-fabrication.Due to the in-trinsic advantage of active tunability by external stimulus,graphene has been successively demonstrated as a favorable candidate to empower metasurfaces with remarkably dynamic tunability,and their recent advances are propelling the EM wave manipulations to a new height:from static to dynamic.Here,we review the recent progress on dynamic metasur-faces and metadevices enabled by graphene with the focus on electrically-controlled dynamic manipulation of the EM waves covering the mid-infrared,terahertz,and microwave regimes.The fundamentals of graphene,including basic ma-terial properties and plasmons,are first discussed.Then,graphene-empowered dynamic metasurfaces and met-adevices are divided into two categories,i.e.,metasurfaces with building blocks of structured graphene and hybrid metasurfaces integrated with graphene,and their recent advances in dynamic spectrum manipulation,wavefront shap-ing,polarization control,and frequency conversion in near/far fields and global/local ways are elaborated.In the end,we summarize the progress,outline the remaining challenges,and prospect the potential future developments.
基金Project supported by National Nature Science Foundation of China （Grant No 60437020） and the Science and Technology Plan Project of Shannxi Province （Grant No 2004K05-G47）.
文摘In this paper, polarization properties and propagation characteristics of polymer photonic crystal fibres with elliptical core and non-hexagonal symmetry structure are investigated by using the full vectorial plane wave method. The results show that the birefringence of the fibre is induced by asymmetries of both the cladding and the core. Moreover, by adjusting the non-symmetrical ratio factor of cladding η from 0.4 to 1 in step 0.1, we find the optimized design parameters of the fibre with high birefringence and limited polarization mode dispersion, operating in a single mode regime at an appropriate wavelength range. The range of wavelength approaches the visible and near-infrared which is consistent with the communication windows of polymer optical fibres.
基金supported by the National Natural Science Foundation of China (Grant No 10674176)
文摘This paper investigates the temporal behaviour of open-circuit bright photovoltaic spatial solitons by using numerical techniques. It shows that when the intensity ratio of the soliton, the ratio between the soliton peak intensity and the dark irradiance, is small, the quasi-steady-state soliton width decreases monotonically with the increase of τ-, where τ- is the parameter correlated with the time, that when the intensity ratio of the soliton is big, the quasi-steady-state soliton width decreases with the increase of τ- and then increases with τ, and that the formation time of the steady-state solitons is not correlated with the intensity ratio of the soliton. It finds that the local nonlinear effect increases with the photovoltaic field, which behaves as that the width of soliton beams is small and the self-focusing quasi-period is short. On the other hand, we also discuss that both the time and the temperature have an effect on the beam bending.
文摘A new prototype of single photon imaging system based on wedge and strip anodes is developed. The prototype can directly measure the intensity and position information for an ultra-weak radiant source which takes on the character of single photons. The image of the ultra-weak radiant source can be reconstructed with a wedge and strip anodes detector and an electronic readout subsystem by photon counting and photon position sensitive detecting in a period of time. With proper evaluation, the prototype reveals a spatial resolution superior to 150μm, a 66-kHz maximal counting rate and a dark-count below 0.67 count /cm^2 s.
基金Project supported by the National High Technology Research and Development Program of China (Grant No. 2011AAxxx2008A)Hundred Talent Program of the Chinese Academy of Sciences (Grant No. J08-029)the Main Direction Program of Knowledge Innovation of the Chinese Academy of Sciences (Grant No. YYYJ-1123-4)
文摘Interdigitated finger capacitance of a continuous-wave terahertz photomixer is calculated using the finite element method.For the frequently used electrode width（0.2 μm） and gap width（1.8 μm）,the finger capacitance increases quasi-quadratically with the number of electrodes increasing.The quasi-quadratic dependence can be explained by a sequence of lumped capacitors connected in parallel.For a photomixer composed of 10 electrodes and 9 photoconductive gaps,the finger capacitance increases as the gap width increases at a small electrode width,and follows the reverse trend at a large electrode width.For a constant electrode width,the finger capacitance first decreases and then slightly increases as the gap broadens until the smallest finger capacitance is formed.We also investigate the finger capacitances at different electrode and gap configurations with the 8 μm × 8 μm photomixer commonly used in previous studies.These calculations lead to a better understanding of the finger capacitance affected by the finger parameters,and should lead to terahertz photomixer optimization.
文摘We propose a novel all-optical format conversion from the return-to-zero （RZ） to the non-return-to-zero （NRZ） based on single semiconductor optical amplifier （SOA） and optical band-pass filter （OBE）. We demonstrate the proof of the principle experiment at 10 Gbps by using the test SOA and OBF converter. The format conversion can be achieved with output extinction ratio of 11.51 dB. The BER is 5.5×10^-9 when the power of NRZ is - 10 dBm. The proposed scheme is robust and potential for applications in optical networks.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10390161 and 30370420.
文摘The optical absorption of GaAs nanorings （NRs） under adc electric field and a terahertz （THz） ac electric field applied in the plane containing the NRs is investigated theoretically. The NRs may enclose some magnetic flux in the presence of a magnetic field perpendicular to the NRs plane. Numerical calculation shows that the excitonic effects are essential to correctly describe the optical absorption in NRs. The applied lateral THz electric field, as well as the dc field leads to reduction, broadening and splitting of the exciton peak. In contrast to the presence of a dc field, significant optical absorption peak arises below the zero-field bandgap in the presence ofa THz electric field at a certain frequency. The optical absorption spectrum depends evidently on the frequency and amplitude of the applied THz field and on the magnetic flux threading the NRs. This promises potential applications of NRs for magneto-optical and THz electro-optical sensing.
基金Supported by the National Natural Science Foundation of China under Grant No 10576037.
文摘Two coupled paralnetric four-wave-mixing processes in Rb atoms are studied using perturbation theory, which reveals clear evidence of tile appearance of quantum beat at 608cm^-1, corresponding to the energy difference of the 7s - 5d states of Rb atoms, in the parametric four-wave-mixing signals. A pump-probe technique is utilized to observe the quantum beat. Tinle-varying characteristics of the quantum beat are investigated using time-dependellt Fourier transform. The results show that the time-varying characteistics of the quantum beat not oldy offers a sensitive detecting method for observing the decay of atomic wave packets, but also provides a potential tool for monitoriHg the dissociation of molecules.
基金Project supported by the Major Program of the National Natural Science Foundation of China （Grant No 10390160）, and the National Natural Science Foundation of China （Grant No 30370420）.
文摘We have performed a full numerical calculation of the Franz-Keldysh （FK） effect on magnetoexcitons in a bulk GaAs semiconductor. By employing an initial wlue method in combination with the application of a perfect matched layer, the numerical effort and storage size are dramatically reduced due to a significant reduction in both computed domain and number of base functions. In the absence of an electric field, the higher magnetoexcitonic peaks show distinct Fano lineshape due to the degeneracy with continuum states of the lower Landau levels. The magnetoexcitons that belong to the zeroth Landau level remain in bound states and lead to Lorentzian lineshape, because they are not degenerated with continuum states. In the presence of an electric field, the FK effect on each magnetoexcitonic resonance can be identified for high magnetic fields. However, for low magnetic fields, the FK oscillations dominate the spectrum structure in the vicinity of the bandgap edge and the magnetoexcitonic resonances dominate the spectrum structure of higher energies. In the moderate electric fields, the interplay of FK effect and magnetoexcitonic resonance leads to a complex and rich structure in the absorption spectrum.
基金supported by the Chinese Academy of Sciences/State Administration of Foreign Experts Affairs (CAS/SAFEA) International Partnership Program for Creative Research Teams
文摘Optical emission spectra of the plasma generated by a 532 nm Nd：YAG laser irra- diation onto a standard aluminum alloy （E414d） was recorded and analyzed. The electron tem- perature was determined using the Boltzmann plot method with three aluminum spectral lines at 236.71 nm, 257.509 nm and 308.215 nm, whereas the electron density was inferred by measuring the Stark broadening line profile of Al（II） 281.619 nm. The experimental results confirmed that the local thermodynamic equilibrium was valid and the plasma was optically thin. The spectral line intensity increased initially with the increase in laser irradiance and saturated at higher Jr- radiance levels. Results showed that the energy losses due to the reflection of laser beam from the plasma itself were insignificant. The absorption in the plasma through inverse bremsstrahlung and two-photon ionization were studied. At the same timer the variation of transition probability ratio of Al（I） 309.28 nm to Al（I） 308.21 nm with laser power density was also studied.
基金supported by the fund from Xi’an Institute of Optics and Precision Mechanics。
文摘With the rapid demand for underwater optical communication(UOC), studies of UOC degradation by oceanic turbulence have attached increasing attention worldwide and become a research hot-spot in recent years. Previous studies used a simplified and inaccurate oceanic turbulence spectrum, in which the eddy diffusivity ratio between temperature and salinity is assumed to be unity and the outer scale of turbulence is assumed to be infinite. However, both assumptions are not true in most of the actual marine environments. In this paper, based on the Rytov theory in weak turbulence, we derive analytical expressions of "the aperture-averaged scintillation index"(SI) for both plane and spherical waves, which can clearly demonstrate how SI is influenced by several key factors in UOC. Then, typical fade statistics of the UOC system in weak turbulence is discussed including the probability of fade, the expected number of fades per time, the mean fade time,signal-to-noise ratio and bit error rate. Our results show that spherical wave is preferable in the UOC system in weak turbulence compared to plane wave, and the aperture-averaged effect has a significant impact on UOC system's performance.Our results can be used to determine those key parameters for designing the UOC system over reasonable ranges.
