Employing the two-state model and the time-dependent wave packet method, we have investigated the influences of the parameters of the intense femtosecond laser field on the evolution of the wave packet, as well as the...Employing the two-state model and the time-dependent wave packet method, we have investigated the influences of the parameters of the intense femtosecond laser field on the evolution of the wave packet, as well as the population of ground and double-minimum electronic states of the NaRb molecule. For the different laser wavelengths, the evolution of the wave packet of 6{ }^1／Sigma ^ ＋ state with time and internuclear distance is different, and the different laser intensity brings different influences on the population of the electronic states of the NaRb molecule. One can control the evolutions of wave packet and the population in each state by varying the laser parameters appropriately, which will be a benefit for the light manipulation of atomic and molecular processes.展开更多
Using a neutral N2 beam as target, this paper studies the dissociation of N2^＋ in intense femtosecond laser fields （45 fs, ～ 1 × 10^16 W/cm^2） at the laser wavelength of 800 nm based on the time-of-flight mas...Using a neutral N2 beam as target, this paper studies the dissociation of N2^＋ in intense femtosecond laser fields （45 fs, ～ 1 × 10^16 W/cm^2） at the laser wavelength of 800 nm based on the time-of-flight mass spectra of N＋ fragment ions. The angular distributions of N^＋ and the laser power dependence of N^＋ yielded from different dissociation pathways show that the dissociation mechanisms mainly proceed through the couplings between the metastable states （A, B and C） and the upper excited states of N^＋.A coupling model of light-dressed potential energy curves of N2^＋ is used to interpret the kinetic energy release of N^＋.展开更多
It has been shown that the femtosecond laser polarization modulation is a very simple and well-established method to control the multi-photon absorption process by the light-matter interaction. Previous studies mainly...It has been shown that the femtosecond laser polarization modulation is a very simple and well-established method to control the multi-photon absorption process by the light-matter interaction. Previous studies mainly focused on the multi- photon absorption control in the weak field. In this paper, we further explore the polarization control behavior of multi- photon absorption process in the intermediate femtosecond laser field. In the weak femtosecond laser field, the second- order perturbation theory can well describe the non-resonant two-photon absorption process. However, the higher order nonlinear effect （e.g., four-photon absorption） can occur in the intermediate femtosecond laser field, and thus it is necessary to establish new theoretical model to describe the multi-photon absorption process, which includes the two-photon and four-photon transitions. Here, we construct a fourth-order perturbation theory to study the polarization control behavior of this multi-photon absorption under the intermediate femtosecond laser field excitation, and our theoretical results show that the two-photon and four-photon excitation pathways can induce a coherent interference, while the coherent interference is constructive or destructive that depends on the femtosecond laser center frequency. Moreover, the two-photon and four- photon transitions have the different polarization control efficiency, and the four-photon absorption can obtain the higher polarization control efficiency. Thus, the polarization control efficiency of the whole excitation process can be increased or decreased by properly designing the femtosecond laser field intensity and laser center frequency. These studies can provide a clear physical picture for understanding and controlling the multi-photon absorption process in the intermediate femtosecond laser field, and also can provide a theoretical guidance for the future experimental realization.展开更多
We experimentally demonstrate the Coulomb explosion process of CS_2 molecule under a near-infrared（800 nm）intense femtosecond laser field by a DC-sliced ion imaging technique. We obtain the DC-sliced images of these...We experimentally demonstrate the Coulomb explosion process of CS_2 molecule under a near-infrared（800 nm）intense femtosecond laser field by a DC-sliced ion imaging technique. We obtain the DC-sliced images of these fragment ions S~＋, S^（2＋）, CS~＋, and CS^（2＋）by breaking one C–S bond, and assign their Coulomb explosion channels by considering their kinetic energy release and angular distribution. We also numerically simulate the dissociation dynamics of parent ions CS_2^（k＋）（k = 2–4） by a Coulomb potential approximation, and obtain the time evolution of Coulomb energy and kinetic energy release, which indicates that the dissociation time of parent ions CS_2^（k＋） decreases with the increase of the charge number k.These experimental and theoretical results can serve as a useful benchmark for those researchers who work in the related area.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
We extend the third perturbation theory to study the polarization control behavior of the intermediate state absorption in Nd^（3＋）ions. The results show that coherent interference can occur between the single-photo...We extend the third perturbation theory to study the polarization control behavior of the intermediate state absorption in Nd^（3＋）ions. The results show that coherent interference can occur between the single-photon and three-photon excitation pathways, and depends on the central frequency of the femtosecond laser field. Moreover,single-photon and three-photon absorptions have different polarization control efficiencies, and the relative weight of three-photon absorption in the whole excitation processes can increase with increasing the laser intensity.Therefore, the enhancement or suppression of the intermediate state absorption can be realized and manipulated by properly designing the intensity and central frequency of the polarization modulated femtosecond laser field.This research can not only enrich theoretical research methods for the up-conversion luminescence manipulation of rare-earth ions, but also can provide a clear physical picture for understanding and controlling multi-photon absorption in a multiple energy level system.展开更多
Besides the diverse investigations on the interactions between intense laser fields and molecular systems,extensive research has been recently dedicated to exploring the response of nanosystems excited by well-tailore...Besides the diverse investigations on the interactions between intense laser fields and molecular systems,extensive research has been recently dedicated to exploring the response of nanosystems excited by well-tailored femtosecond laser fields.Due to the fact that nanostructures hold peculiar effects when illuminated by laser pulses,the underlying mechanisms and the corresponding potential applications can make significant improvements in both fundamental research and development of novel techniques.In this review,we provide a summarization of the strong field ionization occurring on the surface of nanosystems.The molecules attached to the nanoparticle surface perform as the precursor in the ionization and excitation of the whole nanosystem,the fundamental processes of which are yet to be discovered.We discuss the influence on nanoparticle constituents,geometric shapes and sizes,as well as the specific waveforms of the excitation laser fields.The intriguing characteristics observed in surface ion emission reflect how enhanced near field affects the localized ionizations and nanoplasma expansions,thereby paving the way for further precision controls on the light-and-matter interactions in the extreme spatial temporal levels.展开更多
Ionization and dissociation of nitrosyl chloride CINO were studied using femtosecond laser mass spectra technique. Strong fragmental ions NO^＋ and Cl^＋ were observed with the laser intensity varied from 3.2× 10...Ionization and dissociation of nitrosyl chloride CINO were studied using femtosecond laser mass spectra technique. Strong fragmental ions NO^＋ and Cl^＋ were observed with the laser intensity varied from 3.2× 10^14 to 2.5×10^15 W/cm^2. These fragmental ions were attributed to the direct dissociation of the parent ions. Electronic structure calculations were also carried out with Hartree-Fock, density functional and correlated levels of theory to understand the possible fragmentation pathways. The very low N-Cl bond energy in the parent ion of nitrosyl chloride is a clear reason for the absence of CINO^＋ and CIN^＋ ion peaks from the femtosecond laser mass spectrum.展开更多
We studied the ionization and dissociation of polyatomic molecule methane in an intense femtosecond laser field with wavelength of 810 nm and intensities ranging from 1.4 × 1014 to 2.6× 1015 W/cm2 by mass sp...We studied the ionization and dissociation of polyatomic molecule methane in an intense femtosecond laser field with wavelength of 810 nm and intensities ranging from 1.4 × 1014 to 2.6× 1015 W/cm2 by mass spectroscopy. Abundant fragment ions were observed in addition to the strong parent ion. The effect of frequency chirp was investigated and it was found that the negatively chirped pulses dramatically enhanced the dissociation probability, which might, be used to control the dissociation pathways.展开更多
Methanol was irradiated by 80 fs laser pulse, intensity range of 1013-1014 W/cm2. A TOF-mass spectrometer was coupled to the laser system and used to detect the ions produced. The parent ions CH3OH+ appeared firstly a...Methanol was irradiated by 80 fs laser pulse, intensity range of 1013-1014 W/cm2. A TOF-mass spectrometer was coupled to the laser system and used to detect the ions produced. The parent ions CH3OH+ appeared firstly at the laser intensity of 1.4 ×1013 W/cm2. While the laser intensity was gradually increased, the parent ions were dissociated and the primary ions CH2OH+ were given as verified from the irradiation of deuterated methanol (CH3OD) showing the C-H bond cracking firstly. While the laser intensity was further increased to 2.0 ×1013 W/cm2, the C-O bonds of the parent ions also broke to give CH3+. When the laser intensity was higher, smaller fragment ions like CH+, C+, OH+ and O+ also appeared. Among the fragment ions, only H+ ion yield had anisotropic angular distribution dependence on the laser polarization vector in the dissociation of methanol. All the experimental observations show that the dissociation of methanol proceeds through stepwise mechanism but not Coulomb explosion.展开更多
The laser pulse width effect on the dis- sociation probability of CH4+ irradiated by an ultrafast laser has been investigated experimentally and theoretically. The femtosecond laser at 800 nm with an intensity of 8.0 ...The laser pulse width effect on the dis- sociation probability of CH4+ irradiated by an ultrafast laser has been investigated experimentally and theoretically. The femtosecond laser at 800 nm with an intensity of 8.0 × 1013 W/cm2 was used. The ob- served relative yield of the primary fragment ion CH3+ increases with increasing pulse width and tends to saturate when the pulse width is longer than 120 fs. The field-assisted dissociation (FAD) model and quasi-classical trajectory (QCT) calculation were ap- plied to predicting the dissociation probability of CH4+. The calculated probability is corrected with the mo- lecular orientation effect and the spatial distribution of laser intensity. The modified results show that the dissociation requires at least 23 fs and saturates with long pulse widths (≥100 fs). The result is ap- proximately consistent with the experimental observa- tion.展开更多
Photodissociation of cyclopentanone (C5H8O) and cyclohexanone (C6H10O) was studied with 800nm, 50fs laser pulse at intensities of 5.0 - 13.0x10(13) W/cm(2). A time of flight mass spectrometer was employed to detect th...Photodissociation of cyclopentanone (C5H8O) and cyclohexanone (C6H10O) was studied with 800nm, 50fs laser pulse at intensities of 5.0 - 13.0x10(13) W/cm(2). A time of flight mass spectrometer was employed to detect the ion signals. Parent ions dominated at lower laser intensities. Fragmentation of the parent ions increases with increasing laser intensity and molecular size. The fragmentation mechanism was discussed.展开更多
We present in this paper an investigation of the nonlinear process of above-threshold ionization. The process arises when an atomic or molecular system, exposed to an intense laser pulse, continues to absorb more phot...We present in this paper an investigation of the nonlinear process of above-threshold ionization. The process arises when an atomic or molecular system, exposed to an intense laser pulse, continues to absorb more photons than that needed for the ionization to occur. We trigger this nonlinear process in a simple molecular system by exposing it to an intense transform-limited Gaussian laser pulse of 267-nm wavelength which is the third harmonic of an 800-nm wavelength Tisapphire laser. We explore the characteristics of the process by analyzing the kinetic-energy spectra of the electrons ejected from the molecular system under different laser peak intensities.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 10674114 and 10604045)
文摘Employing the two-state model and the time-dependent wave packet method, we have investigated the influences of the parameters of the intense femtosecond laser field on the evolution of the wave packet, as well as the population of ground and double-minimum electronic states of the NaRb molecule. For the different laser wavelengths, the evolution of the wave packet of 6{ }^1／Sigma ^ ＋ state with time and internuclear distance is different, and the different laser intensity brings different influences on the population of the electronic states of the NaRb molecule. One can control the evolutions of wave packet and the population in each state by varying the laser parameters appropriately, which will be a benefit for the light manipulation of atomic and molecular processes.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 10774033,60878018 and 10674036)program for New Century Excellent Talents in University of China (NCET)
文摘Using a neutral N2 beam as target, this paper studies the dissociation of N2^＋ in intense femtosecond laser fields （45 fs, ～ 1 × 10^16 W/cm^2） at the laser wavelength of 800 nm based on the time-of-flight mass spectra of N＋ fragment ions. The angular distributions of N^＋ and the laser power dependence of N^＋ yielded from different dissociation pathways show that the dissociation mechanisms mainly proceed through the couplings between the metastable states （A, B and C） and the upper excited states of N^＋.A coupling model of light-dressed potential energy curves of N2^＋ is used to interpret the kinetic energy release of N^＋.
基金supported by the Program of Introducing Talents of Discipline to Universities(Grant No.B12024)the National Natural Science Foundation of China(Grant Nos.51132004,11474096,11547216,11547220,and 11604199)+1 种基金the Science Fund from the Science and Technology Commission of Shanghai Municipality(Grant No.14JC1401500)the Higher Education Key Program of He’nan Province of China(Grant Nos.17A140025 and 16A140030)
文摘It has been shown that the femtosecond laser polarization modulation is a very simple and well-established method to control the multi-photon absorption process by the light-matter interaction. Previous studies mainly focused on the multi- photon absorption control in the weak field. In this paper, we further explore the polarization control behavior of multi- photon absorption process in the intermediate femtosecond laser field. In the weak femtosecond laser field, the second- order perturbation theory can well describe the non-resonant two-photon absorption process. However, the higher order nonlinear effect （e.g., four-photon absorption） can occur in the intermediate femtosecond laser field, and thus it is necessary to establish new theoretical model to describe the multi-photon absorption process, which includes the two-photon and four-photon transitions. Here, we construct a fourth-order perturbation theory to study the polarization control behavior of this multi-photon absorption under the intermediate femtosecond laser field excitation, and our theoretical results show that the two-photon and four-photon excitation pathways can induce a coherent interference, while the coherent interference is constructive or destructive that depends on the femtosecond laser center frequency. Moreover, the two-photon and four- photon transitions have the different polarization control efficiency, and the four-photon absorption can obtain the higher polarization control efficiency. Thus, the polarization control efficiency of the whole excitation process can be increased or decreased by properly designing the femtosecond laser field intensity and laser center frequency. These studies can provide a clear physical picture for understanding and controlling the multi-photon absorption process in the intermediate femtosecond laser field, and also can provide a theoretical guidance for the future experimental realization.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51132004 and 11474096)the Science and Technology Commission of Shanghai Municipality,China(Grant No.14JC1401500)the support of the NYU-ECNU Institute of Physics at NYU Shanghai,China
文摘We experimentally demonstrate the Coulomb explosion process of CS_2 molecule under a near-infrared（800 nm）intense femtosecond laser field by a DC-sliced ion imaging technique. We obtain the DC-sliced images of these fragment ions S~＋, S^（2＋）, CS~＋, and CS^（2＋）by breaking one C–S bond, and assign their Coulomb explosion channels by considering their kinetic energy release and angular distribution. We also numerically simulate the dissociation dynamics of parent ions CS_2^（k＋）（k = 2–4） by a Coulomb potential approximation, and obtain the time evolution of Coulomb energy and kinetic energy release, which indicates that the dissociation time of parent ions CS_2^（k＋） decreases with the increase of the charge number k.These experimental and theoretical results can serve as a useful benchmark for those researchers who work in the related area.
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Supported by the National Natural Science Foundation of China under Grant Nos 51132004,11474096,11604199,U1704145 and 11747101the Science and Technology Commission of Shanghai Municipality under Grant No 14JC1401500+1 种基金the Henan Provincial Natural Science Foundation of China under Grant No 182102210117the Higher Education Key Program of He’nan Province of China under Grant Nos 17A140025 and 16A140030
文摘We extend the third perturbation theory to study the polarization control behavior of the intermediate state absorption in Nd^（3＋）ions. The results show that coherent interference can occur between the single-photon and three-photon excitation pathways, and depends on the central frequency of the femtosecond laser field. Moreover,single-photon and three-photon absorptions have different polarization control efficiencies, and the relative weight of three-photon absorption in the whole excitation processes can increase with increasing the laser intensity.Therefore, the enhancement or suppression of the intermediate state absorption can be realized and manipulated by properly designing the intensity and central frequency of the polarization modulated femtosecond laser field.This research can not only enrich theoretical research methods for the up-conversion luminescence manipulation of rare-earth ions, but also can provide a clear physical picture for understanding and controlling multi-photon absorption in a multiple energy level system.
基金Project supported by the National Natural Science Fundation of China (Grant Nos.92050105,92250301,and 12227807)。
文摘Besides the diverse investigations on the interactions between intense laser fields and molecular systems,extensive research has been recently dedicated to exploring the response of nanosystems excited by well-tailored femtosecond laser fields.Due to the fact that nanostructures hold peculiar effects when illuminated by laser pulses,the underlying mechanisms and the corresponding potential applications can make significant improvements in both fundamental research and development of novel techniques.In this review,we provide a summarization of the strong field ionization occurring on the surface of nanosystems.The molecules attached to the nanoparticle surface perform as the precursor in the ionization and excitation of the whole nanosystem,the fundamental processes of which are yet to be discovered.We discuss the influence on nanoparticle constituents,geometric shapes and sizes,as well as the specific waveforms of the excitation laser fields.The intriguing characteristics observed in surface ion emission reflect how enhanced near field affects the localized ionizations and nanoplasma expansions,thereby paving the way for further precision controls on the light-and-matter interactions in the extreme spatial temporal levels.
基金Project supported by the Hundred Talent Fund of Chinese Academy of Sciences and the National Natural Science Foundation of China （Nos. 20477047, 20473094）.
文摘Ionization and dissociation of nitrosyl chloride CINO were studied using femtosecond laser mass spectra technique. Strong fragmental ions NO^＋ and Cl^＋ were observed with the laser intensity varied from 3.2× 10^14 to 2.5×10^15 W/cm^2. These fragmental ions were attributed to the direct dissociation of the parent ions. Electronic structure calculations were also carried out with Hartree-Fock, density functional and correlated levels of theory to understand the possible fragmentation pathways. The very low N-Cl bond energy in the parent ion of nitrosyl chloride is a clear reason for the absence of CINO^＋ and CIN^＋ ion peaks from the femtosecond laser mass spectrum.
基金This work was supported by the National Key Basic Research Special Foundation(NKBRSF)under Grant No.G1999075207the National Natural Science Foundation of China under Grant No.19884001,10104003 and 90101027.
文摘We studied the ionization and dissociation of polyatomic molecule methane in an intense femtosecond laser field with wavelength of 810 nm and intensities ranging from 1.4 × 1014 to 2.6× 1015 W/cm2 by mass spectroscopy. Abundant fragment ions were observed in addition to the strong parent ion. The effect of frequency chirp was investigated and it was found that the negatively chirped pulses dramatically enhanced the dissociation probability, which might, be used to control the dissociation pathways.
基金This work was supported by the National Natural Science Foundation of China (Grant No. 29973052) the Ministry of Science & Technology of China.
文摘Methanol was irradiated by 80 fs laser pulse, intensity range of 1013-1014 W/cm2. A TOF-mass spectrometer was coupled to the laser system and used to detect the ions produced. The parent ions CH3OH+ appeared firstly at the laser intensity of 1.4 ×1013 W/cm2. While the laser intensity was gradually increased, the parent ions were dissociated and the primary ions CH2OH+ were given as verified from the irradiation of deuterated methanol (CH3OD) showing the C-H bond cracking firstly. While the laser intensity was further increased to 2.0 ×1013 W/cm2, the C-O bonds of the parent ions also broke to give CH3+. When the laser intensity was higher, smaller fragment ions like CH+, C+, OH+ and O+ also appeared. Among the fragment ions, only H+ ion yield had anisotropic angular distribution dependence on the laser polarization vector in the dissociation of methanol. All the experimental observations show that the dissociation of methanol proceeds through stepwise mechanism but not Coulomb explosion.
文摘The laser pulse width effect on the dis- sociation probability of CH4+ irradiated by an ultrafast laser has been investigated experimentally and theoretically. The femtosecond laser at 800 nm with an intensity of 8.0 × 1013 W/cm2 was used. The ob- served relative yield of the primary fragment ion CH3+ increases with increasing pulse width and tends to saturate when the pulse width is longer than 120 fs. The field-assisted dissociation (FAD) model and quasi-classical trajectory (QCT) calculation were ap- plied to predicting the dissociation probability of CH4+. The calculated probability is corrected with the mo- lecular orientation effect and the spatial distribution of laser intensity. The modified results show that the dissociation requires at least 23 fs and saturates with long pulse widths (≥100 fs). The result is ap- proximately consistent with the experimental observa- tion.
文摘Photodissociation of cyclopentanone (C5H8O) and cyclohexanone (C6H10O) was studied with 800nm, 50fs laser pulse at intensities of 5.0 - 13.0x10(13) W/cm(2). A time of flight mass spectrometer was employed to detect the ion signals. Parent ions dominated at lower laser intensities. Fragmentation of the parent ions increases with increasing laser intensity and molecular size. The fragmentation mechanism was discussed.
文摘We present in this paper an investigation of the nonlinear process of above-threshold ionization. The process arises when an atomic or molecular system, exposed to an intense laser pulse, continues to absorb more photons than that needed for the ionization to occur. We trigger this nonlinear process in a simple molecular system by exposing it to an intense transform-limited Gaussian laser pulse of 267-nm wavelength which is the third harmonic of an 800-nm wavelength Tisapphire laser. We explore the characteristics of the process by analyzing the kinetic-energy spectra of the electrons ejected from the molecular system under different laser peak intensities.
