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
We study the ionization probabilities of atoms by a short laser pulse with three different theoretical methods, i.e., the numerical solution of the time-dependent SchrSdinger equation （TDSE）, the Perelomov-Popov Ter...We study the ionization probabilities of atoms by a short laser pulse with three different theoretical methods, i.e., the numerical solution of the time-dependent SchrSdinger equation （TDSE）, the Perelomov-Popov Terent＇ev （PPT） theory, and the Ammosov-Delone-Krainov （ADK） theory. Our results show that laser intensity dependent ionization probabilities of several atoms （i.e., H, He, and Ne） obtained from the PPT theory accord quite well with the TDSE results both in the multiphoton and tunneling ionization regimes, while the ADK results fit well to the TDSE data only in the tunneling ionization regime. Our calculations also show that laser intensity dependent ionization probabilities of a H atom at three different laser wavelengths of 600 nm, 800 nm, and 1200 nm obtained from the PPT theory are also in good agreement with those from the TDSE, while the ADK theory fails to give the wavelength dependence of ionization probability. Only when the laser wavelength is long enough, will the results of ADK be close to those of TDSE.展开更多
The elaborate energy and momentum spectra of ionized electrons from atoms in laser fields suggest that the ionization dynamics described by tunneling theory should be modified. Although great efforts have been carried...The elaborate energy and momentum spectra of ionized electrons from atoms in laser fields suggest that the ionization dynamics described by tunneling theory should be modified. Although great efforts have been carried out within semiclassical models, there are few discussions describing the multiphoton absorption process within a quantum framework. Comparing the results obtained with the time-dependent Schr?dinger equation(TDSE)and the Keldysh–Faisal–Reiss(KFR) theory, we study the nonperturbative effects of ionization dynamics beyond the KFR theory. The difference in momentum spectra between multiphoton and tunneling regimes is understood in a unified picture with virtual multiphoton absorption processes. For the multiphoton regime, the momentum spectra can be obtained by coherent interference of each periodic contribution. However, the interference of multiphoton absorption peaks will result in a complex structure of virtual multiphoton bands in the tunneling regime. It is shown that the virtual spectra will be almost continuous in the tunneling regime instead of the discrete levels found in the multiphoton regime. Finally, with a model combining the TDSE and the KFR theory,we try to understand the different effects of virtual multiphoton processes on ionization dynamics.展开更多
In this work, we mainly investigate the NH3 molecular multiphoton ionization process by using the photoelectron velocity map imaging technique. Under the condition of femtosecond laser(wavelength at 800 nm), the photo...In this work, we mainly investigate the NH3 molecular multiphoton ionization process by using the photoelectron velocity map imaging technique. Under the condition of femtosecond laser(wavelength at 800 nm), the photoelectron images are detected. The channel switching and above-threshold ionization(ATI) effect are also confirmed. The kinetic energy spectrum(KES) and the photoelectron angular distributions(PADs) are obtained through the anti-Abel transformation from the original images, and then three ionization channels are confirmed successfully according to the Freeman resonance effect in a relatively low laser intensity region. In the excitation process, the intermediate resonance Rydberg states are C^1 A 1(6 + 2 photons process), B^1 E(6 + 2 photons process) and C^1 A 1(7 + 2 photons process), respectively. At the same time, we also find that the photoelectron angular distributions are independent of laser intensity. In addition, the electrons produced by different processes interfere with each other and they can produce a spider-like structure. We also find ac-Stark movement according to the Stark-shift-induced resonance effect when the laser intensity is relatively high.展开更多
This paper studies the multiphoton resonant ionization by two-colour laser pulses in the hydrogen atom by solving the time-dependent Schroedinger equation. By fixing the parameters of fundamental laser field and scann...This paper studies the multiphoton resonant ionization by two-colour laser pulses in the hydrogen atom by solving the time-dependent Schroedinger equation. By fixing the parameters of fundamental laser field and scanning the frequency of second laser field, it finds that the ionization probability shows several resonance peaks and is also much larger than the linear superposition of probabilities by applying two lasers separately. The enhancement of the ionization happens when the system is resonantly pumped to the excited states by absorbing two or more colour photons non-sequentially.展开更多
This paper studies the multiphoton ionization of the hydrogen atom exposed to the linearly or circularly polarized laser pulses by solving the time-dependent SchrSdinger equation. It finds that the ratio of the ioniza...This paper studies the multiphoton ionization of the hydrogen atom exposed to the linearly or circularly polarized laser pulses by solving the time-dependent SchrSdinger equation. It finds that the ratio of the ionization probabilities by linearly and circularly polarized laser pulses varies with the numbers of absorbing photons. With the same laser intensity, the circularly polarized laser pulse favors to ionize the atom with more ease than the linearly polarized laser pulse if only two or three photons are necessary to be absorbed. For the higher order multiphoton ionization, the linearly polarized laser pulse has the advantage over circularly polarized laser pulse to ionize the atom.展开更多
Using the numerical solution of the time-dependent SchrSdinger equation of a one-dimensional model atom in a two-colour laser field, we have investigated the effects of the potential models on coherent control of atom...Using the numerical solution of the time-dependent SchrSdinger equation of a one-dimensional model atom in a two-colour laser field, we have investigated the effects of the potential models on coherent control of atomic multiphoton ionization. It is found that the photoelectron spectra are obviously different for the long-range （Coulomb-like） and short-range （with no excited bound states） potential model atoms, which are produced by two-colour coherent control of atomic multiphoton ionization in a few laser cycles. Our results indicate that two-colour coherent control of atomic multiphoton ionization can be observed in simulations, depending on the choice of the model potentials.展开更多
Multiply charged ions of Ar and NO were observed in MPI experiment Of NO/Ar with TOF-MS. A delayable pulsed acceleration field wn applied tO investigate the effect of the photoelectrons on the formation of the multi...Multiply charged ions of Ar and NO were observed in MPI experiment Of NO/Ar with TOF-MS. A delayable pulsed acceleration field wn applied tO investigate the effect of the photoelectrons on the formation of the multiply charged ions. The multiply charged ions were suggested to be produced by photoelectron impact ionization, in the region bentween the extractor grid and the repeller plate, step by step, from neutral species and lower charged ions. The 50-60ns of FWHM of the ion peaks implies that the pulse width of the photoelectrons should be shorter considering the broadening effect during the ionization process.展开更多
A simple low-cost system for detection of polycyclic aromatic hydrocarbon (PAH) in solution based on multiphoton ionization configuration is designed using a circulating ionization cell of 0.1 × 2 × 5 mm dim...A simple low-cost system for detection of polycyclic aromatic hydrocarbon (PAH) in solution based on multiphoton ionization configuration is designed using a circulating ionization cell of 0.1 × 2 × 5 mm dimension with quartz optical window. Fourth harmonic emission of Nd:YAG laser (266 nm, 6 ns, 10 Hz, and 2 mJ) and second harmonic generation of distributed feedback dye laser (278 - 286 nm, 20 ps, 10 Hz, and 300 μJ) were used as the ionization source. A high voltage of 800 V was applied to separate the ions after ionization. The photocurrent includes a sharp peak and a broad tail indexed to electron and ion currents, respectively. The lowest concentration of anthraxcene (C14H10) in order of few nano-grams per milliliter was detected by this multiphoton ionization configuration.展开更多
We study the multiphoton ionization of potassium atoms in 800 nm and 400 nm femtosecond laser fields.In the 800 nm laser field,the potassium atom absorbs three photons and emits one electron via one photon resonance w...We study the multiphoton ionization of potassium atoms in 800 nm and 400 nm femtosecond laser fields.In the 800 nm laser field,the potassium atom absorbs three photons and emits one electron via one photon resonance with the 4p intermediate state with the help of the ac-Stark shift.The resonance feature is clearly shown as an Autler-Townes(AT) splitting and is mapped out in the electron kinetic energy spectrum.In a 400 nm laser field,although one photon resonance is possible with the 5p state,no splitting is observed.The different transition amplitudes between 4s-4p and 4s-5p explain the observed results.Due to the AT effect,an unexpected peak in the photoelectron energy spectrum that violates the dipole transition rule is observed.A preliminary explanation involving the spin-orbit interaction in the p state is given to account for this component.The observed ATsplitting in the electron kinetic energy distribution can be used as an effective method to calibrate the intensity of a laser field.展开更多
This paper reports that the （2＋1） resonance enhanced multi-photon ionization spectra of SH radical in external fields are simulated using the split-operator scheme of time-dependent wave-packet method. Two ionic st...This paper reports that the （2＋1） resonance enhanced multi-photon ionization spectra of SH radical in external fields are simulated using the split-operator scheme of time-dependent wave-packet method. Two ionic states, i.e. a1△ and b1∑＋, are involved in the simulation. It gives the simulated photoelectron spectra, the population in each electronic state, as well as the projection of the wave-packet in each electronic state on different vibrational states. These results show that the so-called four-state model can represent the experimental results well.展开更多
Multi photon ionization (MPI) in plasma is examined in terms of optical metric, and the quantum Volkov state in curved space time is derived. The cross section of MPI is derived by virtue of the corrected Volkov sta...Multi photon ionization (MPI) in plasma is examined in terms of optical metric, and the quantum Volkov state in curved space time is derived. The cross section of MPI is derived by virtue of the corrected Volkov state within the framework of quantum electrodynamics (QED) formal scattering theory. It shows that the plasma medium acts as a suppression on MPI.展开更多
We present the recent new developments of time-dependent Schrödinger equation and time-dependent density-functional theory for accurate and efficient treatment of the electronic structure and time-dependent quant...We present the recent new developments of time-dependent Schrödinger equation and time-dependent density-functional theory for accurate and efficient treatment of the electronic structure and time-dependent quantum dynamics of many-electron atomic and molecular systems in intense laser fields.We extend time-dependent generalized pseudospectral(TDGPS)numerical method developed for time-dependent wave equations in multielectron systems.The TDGPS method allows us to obtain highly accurate time-dependent wave functions with the use of only a modest number of spatial grid point for complex quantum dynamical calculations.The usefulness of these procedures is illustrated by a few case studies of atomic and molecular processes of current interests in intense laser fields,including multiphoton ionization,above-threshold ionization,high-order harmonic generation,attosecond pulse generation,and quantum dynamical processes related to multielectron effects.We conclude this paper with some open questions and perspectives of multiphoton quantum dynamics of many-electron atomic and molecular systems in intense laser fields.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. 11044007,11164025,and 11064013)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant Nos.20096203110001 and 20116203120001)the Foundation of Northwest Normal University,China (Grant No. NWNU-KJCXGC-03-62)
文摘We study the ionization probabilities of atoms by a short laser pulse with three different theoretical methods, i.e., the numerical solution of the time-dependent SchrSdinger equation （TDSE）, the Perelomov-Popov Terent＇ev （PPT） theory, and the Ammosov-Delone-Krainov （ADK） theory. Our results show that laser intensity dependent ionization probabilities of several atoms （i.e., H, He, and Ne） obtained from the PPT theory accord quite well with the TDSE results both in the multiphoton and tunneling ionization regimes, while the ADK results fit well to the TDSE data only in the tunneling ionization regime. Our calculations also show that laser intensity dependent ionization probabilities of a H atom at three different laser wavelengths of 600 nm, 800 nm, and 1200 nm obtained from the PPT theory are also in good agreement with those from the TDSE, while the ADK theory fails to give the wavelength dependence of ionization probability. Only when the laser wavelength is long enough, will the results of ADK be close to those of TDSE.
基金the National Natural Science Foundation of China under Grant Nos 11725417 and 11575027the Joint Fund of the National Natural Science Foundation of China and the China Academy of Engineering Physics under Grant No U1730449,and the Science Challenge Project under Grant No TZ2018005
文摘The elaborate energy and momentum spectra of ionized electrons from atoms in laser fields suggest that the ionization dynamics described by tunneling theory should be modified. Although great efforts have been carried out within semiclassical models, there are few discussions describing the multiphoton absorption process within a quantum framework. Comparing the results obtained with the time-dependent Schr?dinger equation(TDSE)and the Keldysh–Faisal–Reiss(KFR) theory, we study the nonperturbative effects of ionization dynamics beyond the KFR theory. The difference in momentum spectra between multiphoton and tunneling regimes is understood in a unified picture with virtual multiphoton absorption processes. For the multiphoton regime, the momentum spectra can be obtained by coherent interference of each periodic contribution. However, the interference of multiphoton absorption peaks will result in a complex structure of virtual multiphoton bands in the tunneling regime. It is shown that the virtual spectra will be almost continuous in the tunneling regime instead of the discrete levels found in the multiphoton regime. Finally, with a model combining the TDSE and the KFR theory,we try to understand the different effects of virtual multiphoton processes on ionization dynamics.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11574116,11534004,10704028,and 11474123)
文摘In this work, we mainly investigate the NH3 molecular multiphoton ionization process by using the photoelectron velocity map imaging technique. Under the condition of femtosecond laser(wavelength at 800 nm), the photoelectron images are detected. The channel switching and above-threshold ionization(ATI) effect are also confirmed. The kinetic energy spectrum(KES) and the photoelectron angular distributions(PADs) are obtained through the anti-Abel transformation from the original images, and then three ionization channels are confirmed successfully according to the Freeman resonance effect in a relatively low laser intensity region. In the excitation process, the intermediate resonance Rydberg states are C^1 A 1(6 + 2 photons process), B^1 E(6 + 2 photons process) and C^1 A 1(7 + 2 photons process), respectively. At the same time, we also find that the photoelectron angular distributions are independent of laser intensity. In addition, the electrons produced by different processes interfere with each other and they can produce a spider-like structure. We also find ac-Stark movement according to the Stark-shift-induced resonance effect when the laser intensity is relatively high.
基金supports by the Beijing Key Laboratory for Nano-Photonics and Nano-Structure
文摘This paper studies the multiphoton resonant ionization by two-colour laser pulses in the hydrogen atom by solving the time-dependent Schroedinger equation. By fixing the parameters of fundamental laser field and scanning the frequency of second laser field, it finds that the ionization probability shows several resonance peaks and is also much larger than the linear superposition of probabilities by applying two lasers separately. The enhancement of the ionization happens when the system is resonantly pumped to the excited states by absorbing two or more colour photons non-sequentially.
基金supports by the Beijing Key Laboratory for Nano-Photonics and Nano-Structure
文摘This paper studies the multiphoton ionization of the hydrogen atom exposed to the linearly or circularly polarized laser pulses by solving the time-dependent SchrSdinger equation. It finds that the ratio of the ionization probabilities by linearly and circularly polarized laser pulses varies with the numbers of absorbing photons. With the same laser intensity, the circularly polarized laser pulse favors to ionize the atom with more ease than the linearly polarized laser pulse if only two or three photons are necessary to be absorbed. For the higher order multiphoton ionization, the linearly polarized laser pulse has the advantage over circularly polarized laser pulse to ionize the atom.
基金Project supported by the National Natural Science Foundation of China （Grant No 10674112） and the Young Teachers Foundation of Northwest Normal University （Grant No NWNU-QN-04-25）.
文摘Using the numerical solution of the time-dependent SchrSdinger equation of a one-dimensional model atom in a two-colour laser field, we have investigated the effects of the potential models on coherent control of atomic multiphoton ionization. It is found that the photoelectron spectra are obviously different for the long-range （Coulomb-like） and short-range （with no excited bound states） potential model atoms, which are produced by two-colour coherent control of atomic multiphoton ionization in a few laser cycles. Our results indicate that two-colour coherent control of atomic multiphoton ionization can be observed in simulations, depending on the choice of the model potentials.
文摘Multiply charged ions of Ar and NO were observed in MPI experiment Of NO/Ar with TOF-MS. A delayable pulsed acceleration field wn applied tO investigate the effect of the photoelectrons on the formation of the multiply charged ions. The multiply charged ions were suggested to be produced by photoelectron impact ionization, in the region bentween the extractor grid and the repeller plate, step by step, from neutral species and lower charged ions. The 50-60ns of FWHM of the ion peaks implies that the pulse width of the photoelectrons should be shorter considering the broadening effect during the ionization process.
文摘A simple low-cost system for detection of polycyclic aromatic hydrocarbon (PAH) in solution based on multiphoton ionization configuration is designed using a circulating ionization cell of 0.1 × 2 × 5 mm dimension with quartz optical window. Fourth harmonic emission of Nd:YAG laser (266 nm, 6 ns, 10 Hz, and 2 mJ) and second harmonic generation of distributed feedback dye laser (278 - 286 nm, 20 ps, 10 Hz, and 300 μJ) were used as the ionization source. A high voltage of 800 V was applied to separate the ions after ionization. The photocurrent includes a sharp peak and a broad tail indexed to electron and ion currents, respectively. The lowest concentration of anthraxcene (C14H10) in order of few nano-grams per milliliter was detected by this multiphoton ionization configuration.
基金Supported by the National Key R&D Program of China (Grant No.2019YFA0307701)the National Natural Science Foundation of China (Grant Nos.91850114,11774131,12074143,11704148,11704147,and 11904120)+1 种基金the Science Challenge Project (Grant No.TZ2018005)the finical support of the starting grant from Jilin University。
文摘We study the multiphoton ionization of potassium atoms in 800 nm and 400 nm femtosecond laser fields.In the 800 nm laser field,the potassium atom absorbs three photons and emits one electron via one photon resonance with the 4p intermediate state with the help of the ac-Stark shift.The resonance feature is clearly shown as an Autler-Townes(AT) splitting and is mapped out in the electron kinetic energy spectrum.In a 400 nm laser field,although one photon resonance is possible with the 5p state,no splitting is observed.The different transition amplitudes between 4s-4p and 4s-5p explain the observed results.Due to the AT effect,an unexpected peak in the photoelectron energy spectrum that violates the dipole transition rule is observed.A preliminary explanation involving the spin-orbit interaction in the p state is given to account for this component.The observed ATsplitting in the electron kinetic energy distribution can be used as an effective method to calibrate the intensity of a laser field.
基金Project supported by the National Natural Science Foundation of China (Grant No 10574083)the Natural Science Foundation of Shandong Province of China (Grant No Y2006A23)Partial financial support from the National Basic Research Program of China (Grant No 2006CB806000)
文摘This paper reports that the （2＋1） resonance enhanced multi-photon ionization spectra of SH radical in external fields are simulated using the split-operator scheme of time-dependent wave-packet method. Two ionic states, i.e. a1△ and b1∑＋, are involved in the simulation. It gives the simulated photoelectron spectra, the population in each electronic state, as well as the projection of the wave-packet in each electronic state on different vibrational states. These results show that the so-called four-state model can represent the experimental results well.
文摘Multi photon ionization (MPI) in plasma is examined in terms of optical metric, and the quantum Volkov state in curved space time is derived. The cross section of MPI is derived by virtue of the corrected Volkov state within the framework of quantum electrodynamics (QED) formal scattering theory. It shows that the plasma medium acts as a suppression on MPI.
基金the National Natural Science Foundation of China(Grant Nos.11674268 and 11764038)the Natural Science Foundation of Guangdong Province,China(Grant No.2020A1515010927)Department of Education of Guangdong Province,China(Grant Nos.2018KCXTD011 and 2019KTSCX037).
文摘We present the recent new developments of time-dependent Schrödinger equation and time-dependent density-functional theory for accurate and efficient treatment of the electronic structure and time-dependent quantum dynamics of many-electron atomic and molecular systems in intense laser fields.We extend time-dependent generalized pseudospectral(TDGPS)numerical method developed for time-dependent wave equations in multielectron systems.The TDGPS method allows us to obtain highly accurate time-dependent wave functions with the use of only a modest number of spatial grid point for complex quantum dynamical calculations.The usefulness of these procedures is illustrated by a few case studies of atomic and molecular processes of current interests in intense laser fields,including multiphoton ionization,above-threshold ionization,high-order harmonic generation,attosecond pulse generation,and quantum dynamical processes related to multielectron effects.We conclude this paper with some open questions and perspectives of multiphoton quantum dynamics of many-electron atomic and molecular systems in intense laser fields.
