We theoretically study the photoelectron momentum distributions from multiphoton ionization of a model lithium atom over a range of laser wavelengths from 500 nm to 700 nm by numerically solving the time-dependent Sch...We theoretically study the photoelectron momentum distributions from multiphoton ionization of a model lithium atom over a range of laser wavelengths from 500 nm to 700 nm by numerically solving the time-dependent Schr ¨odinger equation. The photoelectron momentum distributions display many ring-like patterns for the three-photon ionization, which vary dramatically with the change of the laser wavelength. We show that the wavelength-dependent photoelectron energy spectrum can be used to effectively identify the resonant and nonresonant ionization pathways. We also find an abnormal ellipticity dependence of the electron yield for the(2+1) resonance-enhanced ionization via the 4d intermediate state, which is relevant to the two-photon excitation probability from the ground state to the 4d state.展开更多
Coherent superposition of electronic states induces attosecond electron motion in molecules.We theoretically investigate the strong-field ionization of this superposition state by numerically solving the time-dependen...Coherent superposition of electronic states induces attosecond electron motion in molecules.We theoretically investigate the strong-field ionization of this superposition state by numerically solving the time-dependent Schrodinger equation.In the obtained photoelectron momentum distribution,an intriguing bifurcation structure appears in the strong-field holographic interference pattern.We demonstrate that this bifurcation structure directly provides complete information about the status of the transient wave function of the superposition state:the horizontal location of the bifurcation in the momentum distribution reveals the relative phase of the involved components of the superposition state and the vertical position indicates the relative coefficient.Thus,this bifurcation structure takes a snapshot of the transient electron wave packet of the superposition state and provides an intuitive way to monitor electron motion in molecules.展开更多
Tunneling is one of the most fundamental and ubiquitous processes in the quantum world.The question of how long a particle takes to tunnel through a potential barrier has sparked a long-standing debate since the early...Tunneling is one of the most fundamental and ubiquitous processes in the quantum world.The question of how long a particle takes to tunnel through a potential barrier has sparked a long-standing debate since the early days of quantum mechanics.Here,we propose and demonstrate a novel scheme to accurately determine the tunneling time of an electron.In this scheme,a weak laser field is used to streak the tunneling current produced by a strong elliptically polarized laser field in an attoclock configuration,allowing us to retrieve the tunneling ionization time relative to the field maximum with a precision of a few attoseconds.This overcomes the difficulties in previous attoclock measurements wherein the Coulomb effect on the photoelectron momentum distribution has to be removed with theoretical models and it requires accurate information of the driving laser fields.We demonstrate that the tunneling time of an electron from an atom is close to zero within our experimental accuracy.Our study represents a straightforward approach toward attosecond time-resolved imaging of electron motion in atoms and molecules.展开更多
Tunneling ionization of atoms and molecules induced by intense laser pulses contains the contributions of numerous quantum orbits.Identifying the contributions of these orbits is crucial for exploring the application ...Tunneling ionization of atoms and molecules induced by intense laser pulses contains the contributions of numerous quantum orbits.Identifying the contributions of these orbits is crucial for exploring the application of tunneling and for understanding various tunneling-triggered strong-field phenomena.We perform a combined experimental and theoretical study to identify the relative contributions of the quantum orbits corresponding to the electrons tunneling ionized during the adjacent rising and falling quarter cycles of the electric field of the laser pulse.In our scheme,a perturbative second-harmonic field is added to the fundamental driving field.By analyzing the relative phase dependence of the signal in the photoelectron momentum distribution,the relative contributions of these two orbits are unambiguously determined.Our results show that their relative contributions sensitively depend on the longitudinal momentum and modulate with the transverse momentum of the photoelectron,which is attributed to the interference of the electron wave packets of the long orbit.The relative contributions of these orbits resolved here are important for the application of strong-field tunneling ionization as a photoelectron spectroscopy for attosecond time-resolved measurements.展开更多
Interaction of intense laser fields with atoms distorts the bound-state electron cloud.Tracing the temporal response of the electron cloud to the laser field is of fundamental importance for understanding the ultrafas...Interaction of intense laser fields with atoms distorts the bound-state electron cloud.Tracing the temporal response of the electron cloud to the laser field is of fundamental importance for understanding the ultrafast dynamics of various nonlinear phenomena of matter,but it is particularly challenging.Here,we show that the ultrafast response of the atomic electron cloud to the intense high-frequency laser pulses can be probed with the attosecond time-resolved photoelectron holography.In this method,an infrared laser pulse is employed to trigger tunneling ionization of the deforming atom.The shape of the deforming electron cloud is encoded in the hologram of the photoelectron momentum distribution.As a demonstration,by solving the time-dependent Schrödinger equation,we show that the adiabatic deforming of the bound-state electron cloud,as well as the nonadiabatic transition among the distorted states,is successfully tracked with attosecond resolution.Our work films the formation process of the metastable Kramers-Henneberger states in the intense high-frequency laser pulses.This establishes a novel approach for time-resolved imaging of the ultrafast bound-state electron processes in intense laser fields.展开更多
Coupled nuclear and electronic dynamics within a molecule are key to understanding a broad range of fundamental physical and chemical processes.Although probing the coupled vibrational and electronic dynamics was demo...Coupled nuclear and electronic dynamics within a molecule are key to understanding a broad range of fundamental physical and chemical processes.Although probing the coupled vibrational and electronic dynamics was demonstrated,it has so far been challenging to observe the coupling interactions between the rotational and electronic degrees of freedom.Here,we report the first observation of Coriolis coupling,a coupling interaction between nuclear rotational angular momentum and electronic axial angular momentum,during laser-induced molecular fragmentation by tracing the electronic structure of a dissociating O+2 molecule.We observe that the electron density changes its shape from that of a molecularσorbital to a nearly isotropic shape as the internuclear distance goes up to∼20?which results from the transition between nearly degenerate electronic states associated with different rotational angular momenta.Our experiment demonstrates that the breaking of a chemical bond does not occur suddenly during molecular dissociation.Instead,it lasts for a long time of several hundred femtoseconds due to the Coriolis coupling interaction.Our experiment can be extended to complicated molecules,holding the potential of revealing yet unobserved electron–nuclear coupling interactions during ultrafast processes.展开更多
Using the classical-trajectory Monte Carlo model, we have theoretically studied the angular momentum distribution of frustrated tunneling ionization（FTI） of atoms in strong laser fields. Our results show that the an...Using the classical-trajectory Monte Carlo model, we have theoretically studied the angular momentum distribution of frustrated tunneling ionization（FTI） of atoms in strong laser fields. Our results show that the angular momentum distribution of the FTI events exhibits a double-hump structure. With this classical model, we back traced the tunneling coordinates, i.e., the tunneling time and initial transverse momentum at tunneling ionization. It is shown that for the events tunneling ionized at the rising edge of the electric field,the final angular momentum exhibits a strong dependence on the initial transverse momentum at tunneling.While for the events ionized at the falling edge, there is a relatively harder recollision between the returning electron and the parent ion, leading to the angular momentum losing the correlation with the initial transverse momentum. Our study suggests that the angular momentum of the FTI events could be manipulated by controlling the initial coordinates of the tunneling ionization.展开更多
Strong-field tunneling ionization is the first step for a broad class of phenomena in intense laser-atom/molecule interactions. Accurate information about the electron wave packet from strong-field tunneling ionizatio...Strong-field tunneling ionization is the first step for a broad class of phenomena in intense laser-atom/molecule interactions. Accurate information about the electron wave packet from strong-field tunneling ionization of atoms and molecules is of essential importance for understanding various tunneling ionization triggered processes. Here, we survey the property of the electron wave packet in tunneling ionization of molecules with a method based on strong-field photoelectron holography. By solving the time-dependent Schr ¨odinger equation, it is shown that the holographic interference in the photoelectron momentum distribution exhibits the asymmetric behavior with respect to the laser polarization direction, when the molecule is aligned with a nonzero angle to the linearly polarized laser field. We demonstrate that this asymmetry is due to the nonzero initial transverse displacement of the electron wave packet at tunneling. By analyzing the holographic interference, this transverse displacement for the launching of electron wave packet tunneling from the molecules is accurately retrieved. This displacement is directly related to the electron density distribution in molecules, and thus our work developed a novel concept for probing electronic structure in molecules.展开更多
We use an interferometic scheme to extract the phase distribution of the electron wave packet from above-threshold ionization in elliptically polarized laser fields.In this scheme,an electron wave packet released from...We use an interferometic scheme to extract the phase distribution of the electron wave packet from above-threshold ionization in elliptically polarized laser fields.In this scheme,an electron wave packet released from a circularly polarized laser pulse acts as a reference wave and interferes with the electron wave packet ionized by a time-delayed counter-rotating elliptically polarized laser field.The generated vortex-shaped interference pattern in the photoelectron momentum distribution enables us to extract the phase distribution of the electron wave packet in the elliptically polarized laser pulse with high precision.By artificially screening the ionic potential at different ranges when solving the time-dependent Schördinger equation,we find that the angle-dependent phase distribution of the electron wave packet in the elliptically polarized laser field shows an obvious angular shift as compared to the strong-field approximation,whose value is the same as the attoclock shift.We also show that the amplitude of the angle-dependent phase distribution is sensitive to the ellipticity of the laser pulse,providing an alternative way to precisely calibrate the laser ellipticity in the attoclock measurement.展开更多
Factory recirculating aquaculture system(RAS)is facing in a stage of continuous research and technological in-novation.Intelligent aquaculture is an important direction for the future development of aquaculture.Howeve...Factory recirculating aquaculture system(RAS)is facing in a stage of continuous research and technological in-novation.Intelligent aquaculture is an important direction for the future development of aquaculture.However,the RAS nowdays still has poor self-learning and optimal decision-making capabilities,which leads to high aqua-culture cost and low running efficiency.In this paper,a precise aeration strategy based on deep learning is de-signed for improving the healthy growth of breeding objects.Firstly,the situation perception driven by computer vision is used to detect the hypoxia behavior.Then combined with the biological energy model,it is constructed to calculate the breeding objects oxygen consumption.Finally,the optimal adaptive aeration strategy is generated according to hypoxia behavior judgement and biological energy model.Experimental results show that the energy consumption of proposed precise aeration strategy decreased by 26.3%compared with the man-ual control and 12.8%compared with the threshold control.Meanwhile,stable water quality conditions acceler-ated breeding objects growth,and the breeding cycle with the average weight of 400 g was shortened from 5 to 6 months to 3–4 months.展开更多
基金supported by National Key Research and Development Program of China (Grant No. 2019YFA0308300)the National Natural Science Foundation of China (Grant Nos. 12021004 and 61475055)。
文摘We theoretically study the photoelectron momentum distributions from multiphoton ionization of a model lithium atom over a range of laser wavelengths from 500 nm to 700 nm by numerically solving the time-dependent Schr ¨odinger equation. The photoelectron momentum distributions display many ring-like patterns for the three-photon ionization, which vary dramatically with the change of the laser wavelength. We show that the wavelength-dependent photoelectron energy spectrum can be used to effectively identify the resonant and nonresonant ionization pathways. We also find an abnormal ellipticity dependence of the electron yield for the(2+1) resonance-enhanced ionization via the 4d intermediate state, which is relevant to the two-photon excitation probability from the ground state to the 4d state.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11874163,11604108,and 11604388)the Program for HUST Academic Frontier Youth Teamthe Fundamental Research Funds for the Central Universities,China(HUST No.2017KFXKJC002)。
文摘Coherent superposition of electronic states induces attosecond electron motion in molecules.We theoretically investigate the strong-field ionization of this superposition state by numerically solving the time-dependent Schrodinger equation.In the obtained photoelectron momentum distribution,an intriguing bifurcation structure appears in the strong-field holographic interference pattern.We demonstrate that this bifurcation structure directly provides complete information about the status of the transient wave function of the superposition state:the horizontal location of the bifurcation in the momentum distribution reveals the relative phase of the involved components of the superposition state and the vertical position indicates the relative coefficient.Thus,this bifurcation structure takes a snapshot of the transient electron wave packet of the superposition state and provides an intuitive way to monitor electron motion in molecules.
基金the National Key Research and Development Program of China(Grant No.2019YFA0308300)the National Natural Science Foundation of China(Grant Nos.11874163,61475055,and 12021004).
文摘Tunneling is one of the most fundamental and ubiquitous processes in the quantum world.The question of how long a particle takes to tunnel through a potential barrier has sparked a long-standing debate since the early days of quantum mechanics.Here,we propose and demonstrate a novel scheme to accurately determine the tunneling time of an electron.In this scheme,a weak laser field is used to streak the tunneling current produced by a strong elliptically polarized laser field in an attoclock configuration,allowing us to retrieve the tunneling ionization time relative to the field maximum with a precision of a few attoseconds.This overcomes the difficulties in previous attoclock measurements wherein the Coulomb effect on the photoelectron momentum distribution has to be removed with theoretical models and it requires accurate information of the driving laser fields.We demonstrate that the tunneling time of an electron from an atom is close to zero within our experimental accuracy.Our study represents a straightforward approach toward attosecond time-resolved imaging of electron motion in atoms and molecules.
基金This work was supported by the National Key Research and Development Program of China(Grant No.2019YFA0308300)the National Natural Science Foundation of China(Grant Nos.11874163,12021004,11627809,11934006).
文摘Tunneling ionization of atoms and molecules induced by intense laser pulses contains the contributions of numerous quantum orbits.Identifying the contributions of these orbits is crucial for exploring the application of tunneling and for understanding various tunneling-triggered strong-field phenomena.We perform a combined experimental and theoretical study to identify the relative contributions of the quantum orbits corresponding to the electrons tunneling ionized during the adjacent rising and falling quarter cycles of the electric field of the laser pulse.In our scheme,a perturbative second-harmonic field is added to the fundamental driving field.By analyzing the relative phase dependence of the signal in the photoelectron momentum distribution,the relative contributions of these two orbits are unambiguously determined.Our results show that their relative contributions sensitively depend on the longitudinal momentum and modulate with the transverse momentum of the photoelectron,which is attributed to the interference of the electron wave packets of the long orbit.The relative contributions of these orbits resolved here are important for the application of strong-field tunneling ionization as a photoelectron spectroscopy for attosecond time-resolved measurements.
基金National Key Research and Development Program of China(2019YFA0308300)National Natural Science Foundation of China(11874163,12074265 and 12021004)。
文摘Interaction of intense laser fields with atoms distorts the bound-state electron cloud.Tracing the temporal response of the electron cloud to the laser field is of fundamental importance for understanding the ultrafast dynamics of various nonlinear phenomena of matter,but it is particularly challenging.Here,we show that the ultrafast response of the atomic electron cloud to the intense high-frequency laser pulses can be probed with the attosecond time-resolved photoelectron holography.In this method,an infrared laser pulse is employed to trigger tunneling ionization of the deforming atom.The shape of the deforming electron cloud is encoded in the hologram of the photoelectron momentum distribution.As a demonstration,by solving the time-dependent Schrödinger equation,we show that the adiabatic deforming of the bound-state electron cloud,as well as the nonadiabatic transition among the distorted states,is successfully tracked with attosecond resolution.Our work films the formation process of the metastable Kramers-Henneberger states in the intense high-frequency laser pulses.This establishes a novel approach for time-resolved imaging of the ultrafast bound-state electron processes in intense laser fields.
基金supported by the National Key Research and Development Program of China(grant no.2023YFA1406800)the National Natural Science Foundation of China(grant nos.62275085,12021004,11934004,and 12104063).
文摘Coupled nuclear and electronic dynamics within a molecule are key to understanding a broad range of fundamental physical and chemical processes.Although probing the coupled vibrational and electronic dynamics was demonstrated,it has so far been challenging to observe the coupling interactions between the rotational and electronic degrees of freedom.Here,we report the first observation of Coriolis coupling,a coupling interaction between nuclear rotational angular momentum and electronic axial angular momentum,during laser-induced molecular fragmentation by tracing the electronic structure of a dissociating O+2 molecule.We observe that the electron density changes its shape from that of a molecularσorbital to a nearly isotropic shape as the internuclear distance goes up to∼20?which results from the transition between nearly degenerate electronic states associated with different rotational angular momenta.Our experiment demonstrates that the breaking of a chemical bond does not occur suddenly during molecular dissociation.Instead,it lasts for a long time of several hundred femtoseconds due to the Coriolis coupling interaction.Our experiment can be extended to complicated molecules,holding the potential of revealing yet unobserved electron–nuclear coupling interactions during ultrafast processes.
基金supported by the National Natural Science Foundation of China(Nos.11622431 and 61405064)
文摘Using the classical-trajectory Monte Carlo model, we have theoretically studied the angular momentum distribution of frustrated tunneling ionization（FTI） of atoms in strong laser fields. Our results show that the angular momentum distribution of the FTI events exhibits a double-hump structure. With this classical model, we back traced the tunneling coordinates, i.e., the tunneling time and initial transverse momentum at tunneling ionization. It is shown that for the events tunneling ionized at the rising edge of the electric field,the final angular momentum exhibits a strong dependence on the initial transverse momentum at tunneling.While for the events ionized at the falling edge, there is a relatively harder recollision between the returning electron and the parent ion, leading to the angular momentum losing the correlation with the initial transverse momentum. Our study suggests that the angular momentum of the FTI events could be manipulated by controlling the initial coordinates of the tunneling ionization.
基金supported by the National Key Research and Development Program of China (Grant No. 2019YFA0308300)the National Natural Science Foundation of China (Grant Nos. 11874163, 11934006, and12021004)。
文摘Strong-field tunneling ionization is the first step for a broad class of phenomena in intense laser-atom/molecule interactions. Accurate information about the electron wave packet from strong-field tunneling ionization of atoms and molecules is of essential importance for understanding various tunneling ionization triggered processes. Here, we survey the property of the electron wave packet in tunneling ionization of molecules with a method based on strong-field photoelectron holography. By solving the time-dependent Schr ¨odinger equation, it is shown that the holographic interference in the photoelectron momentum distribution exhibits the asymmetric behavior with respect to the laser polarization direction, when the molecule is aligned with a nonzero angle to the linearly polarized laser field. We demonstrate that this asymmetry is due to the nonzero initial transverse displacement of the electron wave packet at tunneling. By analyzing the holographic interference, this transverse displacement for the launching of electron wave packet tunneling from the molecules is accurately retrieved. This displacement is directly related to the electron density distribution in molecules, and thus our work developed a novel concept for probing electronic structure in molecules.
基金the National Natural Science Foundation of China(Grants Nos.11674116,11722432,and 61475055).
文摘We use an interferometic scheme to extract the phase distribution of the electron wave packet from above-threshold ionization in elliptically polarized laser fields.In this scheme,an electron wave packet released from a circularly polarized laser pulse acts as a reference wave and interferes with the electron wave packet ionized by a time-delayed counter-rotating elliptically polarized laser field.The generated vortex-shaped interference pattern in the photoelectron momentum distribution enables us to extract the phase distribution of the electron wave packet in the elliptically polarized laser pulse with high precision.By artificially screening the ionic potential at different ranges when solving the time-dependent Schördinger equation,we find that the angle-dependent phase distribution of the electron wave packet in the elliptically polarized laser field shows an obvious angular shift as compared to the strong-field approximation,whose value is the same as the attoclock shift.We also show that the amplitude of the angle-dependent phase distribution is sensitive to the ellipticity of the laser pulse,providing an alternative way to precisely calibrate the laser ellipticity in the attoclock measurement.
基金supported in part by the Chongqing Municipal Education Commission projects under grant KJCX20-20035,KJQN202200829 and KJQN202300844Chongqing Science and Technology Commission projects under grant CSTB2022BSXM-JCX0117supported in part by Chongqing Technology and Business University projects under GRANT No.(2156004,212017,yjscxx2023-211-69).
文摘Factory recirculating aquaculture system(RAS)is facing in a stage of continuous research and technological in-novation.Intelligent aquaculture is an important direction for the future development of aquaculture.However,the RAS nowdays still has poor self-learning and optimal decision-making capabilities,which leads to high aqua-culture cost and low running efficiency.In this paper,a precise aeration strategy based on deep learning is de-signed for improving the healthy growth of breeding objects.Firstly,the situation perception driven by computer vision is used to detect the hypoxia behavior.Then combined with the biological energy model,it is constructed to calculate the breeding objects oxygen consumption.Finally,the optimal adaptive aeration strategy is generated according to hypoxia behavior judgement and biological energy model.Experimental results show that the energy consumption of proposed precise aeration strategy decreased by 26.3%compared with the man-ual control and 12.8%compared with the threshold control.Meanwhile,stable water quality conditions acceler-ated breeding objects growth,and the breeding cycle with the average weight of 400 g was shortened from 5 to 6 months to 3–4 months.
