The new phenomena induced by femtosecond lasers lead to the new area of ultrafast science.It is a significantchallenge to explain the phenomena associated with complex non-equilibrium and non-linear processes.Although...The new phenomena induced by femtosecond lasers lead to the new area of ultrafast science.It is a significantchallenge to explain the phenomena associated with complex non-equilibrium and non-linear processes.Althoughthere is a growing body of experimental observation,a comprehensive model remains undeveloped.We reviewthe challenges in understanding the photon absorption stage mainly for the femtosecond ablation of wide bandgap materialsat the intensities of 10^(13)～10^(14) W/cm^2.Major opinions and challenges in ionization mechanisms are presentedby primarily considering multiphoton ionization and avalanche ionization.展开更多
The multiphoton ionization dissociation of HFC 152a and HFC 134a under the irradiation of 355 nm and 266 nm was studied in this work. Their photolyzed products were analyzed by time of flight mass spectrum instrument....The multiphoton ionization dissociation of HFC 152a and HFC 134a under the irradiation of 355 nm and 266 nm was studied in this work. Their photolyzed products were analyzed by time of flight mass spectrum instrument. The photolyzed products of HFC 152a include H +( m/z =1), C +( m/z =12), CH + 3( m/z =15), C + 2( m/z =24), CF 2H +( m/z =51), and CF +( m/z =31), whereas there is no clear products for HFC 134a photolyzation. Further, the application prospects of HFC 152a and HFC 134a in refrigeration sector were also evaluated from the view point of environmental protection, synthesis conditions and usage performance. It is suggested that HFC 152a is a better alternative compared to HFC 134a in refrigeration sector.展开更多
Photoionization and photodissociation of CH3CN were studied by a linear time of flight mass spectrometer coupled with 800 nm, 50 fs laser pulses at intensities of 6.3×1013-1.2×1014 W/cm2. The laser power dep...Photoionization and photodissociation of CH3CN were studied by a linear time of flight mass spectrometer coupled with 800 nm, 50 fs laser pulses at intensities of 6.3×1013-1.2×1014 W/cm2. The laser power dependences for principal ions CH3CN+, CH2CN+, CHCN+ and CCN+ were measured, which are consistent with the numbers of photons required to produce the ions via multiphoton ionization and dissociation. The results show that eight-photon non-resonant multiphoton ionization is the main photoionization mechanism of the parent ion CH3CN+, while the fragment ions were produced through the dissociation of the molecules in the super-excited states.展开更多
We investigate the high-order harmonic generation from an atom prepared in a superposition of ground state and highly excited state. When the atom is irradiated by an ultrashort pulse, the cutoff position of the plate...We investigate the high-order harmonic generation from an atom prepared in a superposition of ground state and highly excited state. When the atom is irradiated by an ultrashort pulse, the cutoff position of the plateau in the harmonic spectrum is largely extended compared with the case that the atom is initially in the ground state. The physics of the extension of the high-order harmonic plateau can be interpreted by the spatial structure of the atomic initial wave packet. We can optimize the generation of high-order harmonics by substituting the excited state for a particular coherent superposition of some highly excited states to form a spatially localized excited wave packet.展开更多
The wave packet dynamics of I2^- anions is studied by using the time-dependent wave packet method. Two conclusions can be drawn from the calculations. First, the period of the total photoelectron signal oscillating wi...The wave packet dynamics of I2^- anions is studied by using the time-dependent wave packet method. Two conclusions can be drawn from the calculations. First, the period of the total photoelectron signal oscillating with the propagation of delay time is about 750fs. Second, the photoionization of I2^- anions begin at the time 600 fs, and the time needed for the population of the electronic state of I2 neutral molecule to reach the maximum becomes shorter with the increasing delay time.展开更多
The Autler-Townes （AT） splitting in femtosecond photoelectron spectrum of three-level Li2 molecules is theoretically investigated using time-dependent quantum wave packet method. With proper femtosecond laser pulses...The Autler-Townes （AT） splitting in femtosecond photoelectron spectrum of three-level Li2 molecules is theoretically investigated using time-dependent quantum wave packet method. With proper femtosecond laser pulses, three peaks of the AT splitting can be observed in the photoelectron spectrum. The AT splitting stems from rapid Rabi oscillation caused by intense ultrashort laser pluses. The effects of laser parameters on the molecular ionization dynamics are also discussed.展开更多
We report on the observation of ultracold ground electric-state cesium molecules produced directly in a magneto-optical trap with a good signal-to-noise ratio. These molecules arise from the photoassociation of magnet...We report on the observation of ultracold ground electric-state cesium molecules produced directly in a magneto-optical trap with a good signal-to-noise ratio. These molecules arise from the photoassociation of magneto-optical trap lasers and they are detected by resonantly enhanced multiphoton ionization technology. The production rate of ultracold cesium molecules is up to 4× 10^4 s-1. We measure the characteristic time of the ground electric-state cesium molecules generated in the experiment and investigate the Cs2＋ molecular ion intensity as a function of the trapping laser intensity and the ionization pulse laser energy. We conclude that the production of cold cesium molecules may be enhanced by using appropriate experimental parameters, which is useful for future experiments involving the production and trapping of ultracold ground electric-state molecules.展开更多
基金supported by the National Natural Science Foundation of China(50705009)the 111 project China(B08043)+3 种基金the National“863”project of China(2008AA03Z301)the Changjiang Scholar Program of Chinathe Air Force Research Laboratory USA(FA8650-04-C-5704)the National Science Foundation USA(0423233)
文摘The new phenomena induced by femtosecond lasers lead to the new area of ultrafast science.It is a significantchallenge to explain the phenomena associated with complex non-equilibrium and non-linear processes.Althoughthere is a growing body of experimental observation,a comprehensive model remains undeveloped.We reviewthe challenges in understanding the photon absorption stage mainly for the femtosecond ablation of wide bandgap materialsat the intensities of 10^(13)～10^(14) W/cm^2.Major opinions and challenges in ionization mechanisms are presentedby primarily considering multiphoton ionization and avalanche ionization.
文摘The multiphoton ionization dissociation of HFC 152a and HFC 134a under the irradiation of 355 nm and 266 nm was studied in this work. Their photolyzed products were analyzed by time of flight mass spectrum instrument. The photolyzed products of HFC 152a include H +( m/z =1), C +( m/z =12), CH + 3( m/z =15), C + 2( m/z =24), CF 2H +( m/z =51), and CF +( m/z =31), whereas there is no clear products for HFC 134a photolyzation. Further, the application prospects of HFC 152a and HFC 134a in refrigeration sector were also evaluated from the view point of environmental protection, synthesis conditions and usage performance. It is suggested that HFC 152a is a better alternative compared to HFC 134a in refrigeration sector.
文摘Photoionization and photodissociation of CH3CN were studied by a linear time of flight mass spectrometer coupled with 800 nm, 50 fs laser pulses at intensities of 6.3×1013-1.2×1014 W/cm2. The laser power dependences for principal ions CH3CN+, CH2CN+, CHCN+ and CCN+ were measured, which are consistent with the numbers of photons required to produce the ions via multiphoton ionization and dissociation. The results show that eight-photon non-resonant multiphoton ionization is the main photoionization mechanism of the parent ion CH3CN+, while the fragment ions were produced through the dissociation of the molecules in the super-excited states.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10474028 and 10604021.
文摘We investigate the high-order harmonic generation from an atom prepared in a superposition of ground state and highly excited state. When the atom is irradiated by an ultrashort pulse, the cutoff position of the plateau in the harmonic spectrum is largely extended compared with the case that the atom is initially in the ground state. The physics of the extension of the high-order harmonic plateau can be interpreted by the spatial structure of the atomic initial wave packet. We can optimize the generation of high-order harmonics by substituting the excited state for a particular coherent superposition of some highly excited states to form a spatially localized excited wave packet.
基金Supported by the National Natural Science Foundation of China under Grant No 10575017. The code used in our calculation is provided by Professor Ke-Li Han and we appreciate his help and kind advice.
文摘The wave packet dynamics of I2^- anions is studied by using the time-dependent wave packet method. Two conclusions can be drawn from the calculations. First, the period of the total photoelectron signal oscillating with the propagation of delay time is about 750fs. Second, the photoionization of I2^- anions begin at the time 600 fs, and the time needed for the population of the electronic state of I2 neutral molecule to reach the maximum becomes shorter with the increasing delay time.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10374012 and 10674022.
文摘The Autler-Townes （AT） splitting in femtosecond photoelectron spectrum of three-level Li2 molecules is theoretically investigated using time-dependent quantum wave packet method. With proper femtosecond laser pulses, three peaks of the AT splitting can be observed in the photoelectron spectrum. The AT splitting stems from rapid Rabi oscillation caused by intense ultrashort laser pluses. The effects of laser parameters on the molecular ionization dynamics are also discussed.
基金supported by the National Key Fundamental Basic Research Program of China (Grant No. 2006CB921603)the Major Program of National Natural Science Foundation of China (Grant No. 10934004)+3 种基金the National Natural Science Foundation of China (Grant Nos. 60978018,60808009,61008012,and 60978001)the New Teacher Fund of the Ministry of Education of China(Grant No. 200801081021)the National Natural Science Foundation of China for Excellent Research Team (Grant No. 60821004)the Natural Science Foundation of Shanxi Province of China (Grant No. 2009011059-2)
文摘We report on the observation of ultracold ground electric-state cesium molecules produced directly in a magneto-optical trap with a good signal-to-noise ratio. These molecules arise from the photoassociation of magneto-optical trap lasers and they are detected by resonantly enhanced multiphoton ionization technology. The production rate of ultracold cesium molecules is up to 4× 10^4 s-1. We measure the characteristic time of the ground electric-state cesium molecules generated in the experiment and investigate the Cs2＋ molecular ion intensity as a function of the trapping laser intensity and the ionization pulse laser energy. We conclude that the production of cold cesium molecules may be enhanced by using appropriate experimental parameters, which is useful for future experiments involving the production and trapping of ultracold ground electric-state molecules.
