Multiphoton resonant excitation and frustrated tunneling ionization,manifesting the photonic and optical nature of the driving light via direct excitation and electron recapture,respectively,are complementary mechanis...Multiphoton resonant excitation and frustrated tunneling ionization,manifesting the photonic and optical nature of the driving light via direct excitation and electron recapture,respectively,are complementary mechanisms to access Rydberg state excitation(RSE)of atoms and molecules in an intense laser field.However,clear identification and manipulation of their individual contributions in the light-induced RSE process remain experimentally challenging.Here,we bridge this gap by exploring the dissociative and nondissociative RSE of H2 molecules using bicircular two-color laser pulses.Depending on the relative field strength and polarization helicity of the two colors,the RSE probability can be boosted by more than one order of magnitude by exploiting the laser waveform-dependent field effect.The role of the photon effect is readily strengthened with increasing relative strength of the second-harmonic field of the two colors regardless of the polarization helicity.As compared to the nondissociative RSE forming H2,the field effect in producing the dissociative RSE channel of eHt;HT is moderately suppressed,which is primarily accessed via a three-step sequential process separated by molecular bond stretching.Our work paves the way toward a comprehensive understanding of the interplay of the underlying field and photon effects in the strong-field RSE process,as well as facilitating the generation of Rydberg states optimized with tailored characteristics.展开更多
The 4f^76s（~9S）np 8 P J （J = 5/2, 7/2, 9/2） Rydberg series converging to the first ionization limit 4f 7 6s 9 S 4 of the Eu atom using the three-step laser excitation and electric-field-ionization （EFI） method a...The 4f^76s（~9S）np 8 P J （J = 5/2, 7/2, 9/2） Rydberg series converging to the first ionization limit 4f 7 6s 9 S 4 of the Eu atom using the three-step laser excitation and electric-field-ionization （EFI） method are studied. First, the Eu atom is excited from the 4f 7 6s 2 8 S o 7/2 ground state to the 4f 7 6s7s 8 S o 7/2 state through the 4f 7 6s6p 10 P 9/2 state by the first two dye lasers. Next, it is populated to many higher-n members of the 4f 7 6s（ 9 S）np 8 P J Rydberg series by the third dye laser whose wavelength is scanned within a certain range. Finally, the atom in these higher-n states is ionized by the external pulsed electric field. With the field strength up to 2 kV/cm, we can detect the atom in 4f 7 6s（ 9 S）np 8 P J states with n 40. With the given laser line width, the level energies of Rydberg states with n as high as 72 can be determined. We not only confirm the previous data on the 4f 7 6s（ 9 S） np 8 P J Rydberg series, but also extend the n-value assignment significantly by detecting more states.展开更多
The basic process of re-ionization loss was studied.In the drift duct there are three processes leading to re-ionization loss：the collision of neutral beam particles with the molecules of background gas,similar colli...The basic process of re-ionization loss was studied.In the drift duct there are three processes leading to re-ionization loss：the collision of neutral beam particles with the molecules of background gas,similar collisions with released molecules from the inner wall of the drift duct and the ferret-collisions among particles with different energy of the neutral beam.Mathematical models have been developed and taking EAST-NBI parameters as an example,the re-ionization loss was obtained within these models.The result indicated that in the early stage of the neutral beam injector operation the released gas was quite abundant.The amount of re-ionization loss owing to the released gas can be as high as 60%.In the case of a long-time operation of the neutral beam injector,the total re-ionization loss decreases from 13.7% to 5.7%.Then the reionization loss originating mainly from the collisions between particles of the neutral beam and the background molecules is dominant,covering about 92% of the total re-ionization loss.The drift duct pressure was the decisive factor for neutral beam re-ionization loss.展开更多
We study the double ionization process of atoms in intense laser fields. The momentum distributions of the correlated electrons are calculated. Contrary to the general expectation, we show an increasing proportion of ...We study the double ionization process of atoms in intense laser fields. The momentum distributions of the correlated electrons are calculated. Contrary to the general expectation, we show an increasing proportion of the electrons ionized via excitation with the increasing laser intensity. These electrons generally have small energy thus they concentratedly distribute on the central region of the momentum diagram. Consequently, the central part of the momentum diagram becomes more notable in higher intensity laser fields. Further study suggests that this phenomenon is general in double ionization.展开更多
The ionization characteristics of the analytes in a low power Ar microwave plasma torch (MPT) was studied. The influence of forward microwave power, the flow rate of carrier gas and matrix element on the degree of ion...The ionization characteristics of the analytes in a low power Ar microwave plasma torch (MPT) was studied. The influence of forward microwave power, the flow rate of carrier gas and matrix element on the degree of ionization were observed. The axial profiles of the degree of the ionization of some elements were determined. The experimental results are very important for developing the new analytical source——microwave plasma torch (MPT).展开更多
The electron-impact ionization of lithium-like ions C^(3+),N^(4+),O^(5+),Ne^(7+),and Fe2^(3+)is studied using a combination of two-potential distorted-wave and R-matrix methods with a relativistic correction.Total cro...The electron-impact ionization of lithium-like ions C^(3+),N^(4+),O^(5+),Ne^(7+),and Fe2^(3+)is studied using a combination of two-potential distorted-wave and R-matrix methods with a relativistic correction.Total cross sections are computed for incident energies from 1 to 10 times of ionization energy and better agreements with the experimental results are obtained in comparison with the theoretical data available.It is found that the indirect ionization processes become significant for the incident energy larger than about four times of the ionization energy.Contributions from the exchange effects along the isoelectronic sequence are also discussed and found to be important.The present method can be used to obtain systematic ionization cross sections for highly charged ions across a wide incident energy range.展开更多
The formation of plasma bullets’ring-shaped structure in atmospheric pressure helium is analyzed by using a coupled fluid model.The model consists of a two-dimension neutral gas flow module and a one-dimension plasma...The formation of plasma bullets’ring-shaped structure in atmospheric pressure helium is analyzed by using a coupled fluid model.The model consists of a two-dimension neutral gas flow module and a one-dimension plasma dynamics module.The obtained radial distributions of the electron’s number density and the nitrogen’s metastable number density have different structures under different types of reactions or air contents in the model.It shows that total electron impact ionization plays an important role in sustaining the discharge,and together with Penning process,they lead to the shifted-off structure of electron number density.Meanwhile,the ring structure of plasma bullets forms mainly due to the excitation reaction of nitrogen molecule on air contents.展开更多
X-ray emission,as one of the important consequential results from ion-atom collision,carries the important information of several inner-shell processes as primary ionization,vacancy decay and intra-atomic excitation,w...X-ray emission,as one of the important consequential results from ion-atom collision,carries the important information of several inner-shell processes as primary ionization,vacancy decay and intra-atomic excitation,which provides a valid method to investigate the particle properties and the complex interaction mechanism.In our previous work,such multiple ionization of projectile has been observed and the effect of incident energy was verified 30.Here,we would like to present the further plan in which a special attention is going to focus on the dependence of multiple ionization on projectile charge state and target atomic number.展开更多
Ion irradiation of polymers can induce irreversible changes in their macroscopic propcrties.Electronic excitation,ionization,chains scission and cross-links as well as mass losses are acccpted as the fundamental event...Ion irradiation of polymers can induce irreversible changes in their macroscopic propcrties.Electronic excitation,ionization,chains scission and cross-links as well as mass losses are acccpted as the fundamental events that givc rise to the observed macroscopic changes.In this work PET films were irradiated with high-展开更多
基金the National Key R&D Program of China(Grant No.2018YFA0306303)the National Natural Science Foundation of China(Grant Nos.11834004,61690224,92150105,11904103,12241407,and 12227807)the Science and Technology Commission of Shanghai Municipality(Grant No.21ZR1420100).
文摘Multiphoton resonant excitation and frustrated tunneling ionization,manifesting the photonic and optical nature of the driving light via direct excitation and electron recapture,respectively,are complementary mechanisms to access Rydberg state excitation(RSE)of atoms and molecules in an intense laser field.However,clear identification and manipulation of their individual contributions in the light-induced RSE process remain experimentally challenging.Here,we bridge this gap by exploring the dissociative and nondissociative RSE of H2 molecules using bicircular two-color laser pulses.Depending on the relative field strength and polarization helicity of the two colors,the RSE probability can be boosted by more than one order of magnitude by exploiting the laser waveform-dependent field effect.The role of the photon effect is readily strengthened with increasing relative strength of the second-harmonic field of the two colors regardless of the polarization helicity.As compared to the nondissociative RSE forming H2,the field effect in producing the dissociative RSE channel of eHt;HT is moderately suppressed,which is primarily accessed via a three-step sequential process separated by molecular bond stretching.Our work paves the way toward a comprehensive understanding of the interplay of the underlying field and photon effects in the strong-field RSE process,as well as facilitating the generation of Rydberg states optimized with tailored characteristics.
基金supported by the National Natural Science Foundation of China (No. 10674102)the Natural Science Foundation of Tianjin (No.05YFJMJC05200)
文摘The 4f^76s（~9S）np 8 P J （J = 5/2, 7/2, 9/2） Rydberg series converging to the first ionization limit 4f 7 6s 9 S 4 of the Eu atom using the three-step laser excitation and electric-field-ionization （EFI） method are studied. First, the Eu atom is excited from the 4f 7 6s 2 8 S o 7/2 ground state to the 4f 7 6s7s 8 S o 7/2 state through the 4f 7 6s6p 10 P 9/2 state by the first two dye lasers. Next, it is populated to many higher-n members of the 4f 7 6s（ 9 S）np 8 P J Rydberg series by the third dye laser whose wavelength is scanned within a certain range. Finally, the atom in these higher-n states is ionized by the external pulsed electric field. With the field strength up to 2 kV/cm, we can detect the atom in 4f 7 6s（ 9 S）np 8 P J states with n 40. With the given laser line width, the level energies of Rydberg states with n as high as 72 can be determined. We not only confirm the previous data on the 4f 7 6s（ 9 S） np 8 P J Rydberg series, but also extend the n-value assignment significantly by detecting more states.
基金Supported by National Science Foundation Project (10875146,10575105)Chinese Academy of Sciences Knowledge Innovation Project the Study of Neutral Beam Steady-State Operation of the Key Technical and Physical Problems
文摘The basic process of re-ionization loss was studied.In the drift duct there are three processes leading to re-ionization loss：the collision of neutral beam particles with the molecules of background gas,similar collisions with released molecules from the inner wall of the drift duct and the ferret-collisions among particles with different energy of the neutral beam.Mathematical models have been developed and taking EAST-NBI parameters as an example,the re-ionization loss was obtained within these models.The result indicated that in the early stage of the neutral beam injector operation the released gas was quite abundant.The amount of re-ionization loss owing to the released gas can be as high as 60%.In the case of a long-time operation of the neutral beam injector,the total re-ionization loss decreases from 13.7% to 5.7%.Then the reionization loss originating mainly from the collisions between particles of the neutral beam and the background molecules is dominant,covering about 92% of the total re-ionization loss.The drift duct pressure was the decisive factor for neutral beam re-ionization loss.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61475168,11674231,and 61575124)Natural Science Foundation of Shanghai,China(Grant No.15ZR1430600)Shanghai Gaofeng & Gaoyuan Project for University Academic Program Development,China
文摘We study the double ionization process of atoms in intense laser fields. The momentum distributions of the correlated electrons are calculated. Contrary to the general expectation, we show an increasing proportion of the electrons ionized via excitation with the increasing laser intensity. These electrons generally have small energy thus they concentratedly distribute on the central region of the momentum diagram. Consequently, the central part of the momentum diagram becomes more notable in higher intensity laser fields. Further study suggests that this phenomenon is general in double ionization.
基金Supported by the National Natural Science Foundation of China
文摘The ionization characteristics of the analytes in a low power Ar microwave plasma torch (MPT) was studied. The influence of forward microwave power, the flow rate of carrier gas and matrix element on the degree of ionization were observed. The axial profiles of the degree of the ionization of some elements were determined. The experimental results are very important for developing the new analytical source——microwave plasma torch (MPT).
基金the National Natural Science Foundation of China(Grant Nos.11934004 and U1832201)the Science Challenge Project(Grant No.TZ2016005)the CAEP Foundation(Grant No.CX2019022).
文摘The electron-impact ionization of lithium-like ions C^(3+),N^(4+),O^(5+),Ne^(7+),and Fe2^(3+)is studied using a combination of two-potential distorted-wave and R-matrix methods with a relativistic correction.Total cross sections are computed for incident energies from 1 to 10 times of ionization energy and better agreements with the experimental results are obtained in comparison with the theoretical data available.It is found that the indirect ionization processes become significant for the incident energy larger than about four times of the ionization energy.Contributions from the exchange effects along the isoelectronic sequence are also discussed and found to be important.The present method can be used to obtain systematic ionization cross sections for highly charged ions across a wide incident energy range.
基金Project supported by National Natural Science Foundation of China （10775026 11275042）, Hebei Provincial Natural Science Foundation of China （A2012201015）.
文摘The formation of plasma bullets’ring-shaped structure in atmospheric pressure helium is analyzed by using a coupled fluid model.The model consists of a two-dimension neutral gas flow module and a one-dimension plasma dynamics module.The obtained radial distributions of the electron’s number density and the nitrogen’s metastable number density have different structures under different types of reactions or air contents in the model.It shows that total electron impact ionization plays an important role in sustaining the discharge,and together with Penning process,they lead to the shifted-off structure of electron number density.Meanwhile,the ring structure of plasma bullets forms mainly due to the excitation reaction of nitrogen molecule on air contents.
基金National Key R&D Program of China(2017YFA0402300)National Natural Science Foundation of China(U1532263,11505248,11775042,11775278)。
文摘X-ray emission,as one of the important consequential results from ion-atom collision,carries the important information of several inner-shell processes as primary ionization,vacancy decay and intra-atomic excitation,which provides a valid method to investigate the particle properties and the complex interaction mechanism.In our previous work,such multiple ionization of projectile has been observed and the effect of incident energy was verified 30.Here,we would like to present the further plan in which a special attention is going to focus on the dependence of multiple ionization on projectile charge state and target atomic number.
文摘Ion irradiation of polymers can induce irreversible changes in their macroscopic propcrties.Electronic excitation,ionization,chains scission and cross-links as well as mass losses are acccpted as the fundamental events that givc rise to the observed macroscopic changes.In this work PET films were irradiated with high-
