Above-Threshold Ionization of Xenon by Chirped Intense Laser Pulses

We experimentally investigate above-threshold ionization of xenon subject to chirped intense laser pulses. While for few-cycle laser pulses free of chirp, the Freeman resonance narrow peaks in the photoelectron spectra become strongly suppressed, they will re-emerge for laser pulses with a certain chirp. Moreover, the position of the resonant peaks exhibits a strong dependence on the direction of the chirp. The experimental features can be understood by a two-step ionization process; that is, a multi-photon excitation plus subsequent ionization process.     

电场中Rydberg原子的常数标度能谱方法

标度能谱理论能够简化外场谱及可以经典方法理解原子外场谱而倍受关注。本文报道了用于电场中Rydberg原子常数标度能谱实验研究的装置以及有关的计算机控制、采集及处理系统。该系统对能量E和电场F进行同步控制以保持标度能谱ε=E/F为常数，并成功地得到Rydberg态Sr原子在标度能ε=-3.0时的标度能谱，经过傅里叶变换，获得了电场中Sr原子的电子回归谱。     

纠缠态原子与相干光场作用的量子信息保真度

研究了初始处于纠缠态的双原子与相干光场的相互作用。结果表明,不同的失谐量和初始平均光子数使得系统、原子和光场的量子信息保真度发生改变。     

光腔衰荡技术与高灵敏吸收探测

腔衰荡光谱技术是一种新兴的主灵敏吸收光谱探测技术,已经被广泛地应用于原子、分子、团簇等吸收光谱的测量,且可实现10^-6－10^-14cm^-1量级吸收的测量,文章综述了腔衰荡光谱技术的发展及在吸收光谱探测上的应用。     

Coulomb potential influence in the attoclock experimental scheme

Coulomb potential may induce a significant angular offset to the two-dimensional photoelectron momentum distributions for atoms subject to strong elliptically polarized laser fields.In the attoclock experiment,this offset usually cannot be easily disentangled from the contribution of tunneling delay and poses a main obstacle to the precise measurement of tunneling delay.Based on semiclassical calculations,here,we propose a method to extract the equivalent temporal offset induced solely by Coulomb potential(TOCP)in an attoclock experiment.Our calculations indicate that,at constant laser intensity,the TOCP shows distinctive wavelength dependence laws for different model atoms,and the ratio of the target atom’s TOCP to that of H becomes insensitive to wavelength and linearly proportional to(2Ip)?3/2,where Ip is the ionization potential of the target atom.This wavelength and Ip dependence of TOCP can be further applied to extract the Coulomb potential influence.Our work paves the way for an accurate measurement of the tunneling delay in the tunneling ionization of atoms subject to intense elliptically polarized laser fields.     

Ba原子6s6p1P1←6s6s1S0跃迁的光腔衰荡光谱

建立了一套光腔衰荡原子束吸收光谱测量装置,并对Ba原子的6s6p¹P₁←6s6s¹S₀吸收谱线用光腔衰荡光谱方法进行了测量,得到了Ba原子在553.548nm不同温度下的吸收谱线线型.实验结果表明,该装置测量吸收灵敏度达到6×10^-7. 关键词： 光腔衰荡 吸收光谱 Ba原子     

Tunneling between double wells of atom in crossed electromagnetic fields

The tunneling between double wells of atom in crossed electromagnetic fields is investigated by a one-dimensional Hamiltonian model.The crossed fields induced outer well is apart from the nuclear origin and it is very difficult to access by means of spectroscopy but it will be possible if there exists the tunneling of the electron between the outer well and the Coulomb potential predominated well at the nuclear origin.A one-dimensional quantum calculation with B-spline basis has been performed for hydrogen atom in crossed fields accessible in our laboratory,at B=0.8 T and F= 220 V·cm 1.The calculation shows that the wavefunctions of some excited states close to the Stark saddle point in the outer well extend over to the Coulomb potential well,making it possible to penetrate the quantum information of the outer well.However,the tunneling rate is very small and the spectral measurement of the transitions from the ground state should be of a high resolution and high sensitivity.     

甲胺分子多光子电离质谱研究

胜多光子电离飞行时间质谱法，利用可调谐脉冲激光器，测得了甲胺分子在不同激光波长和激光功率下的多光子电离和解离产物。母体离子ＣＨ３ＮＨ＾＋２的离解速常数随激光发波长的增大而减小。     

Photodetachment of H- near an elastic surface in a magnetic field

This paper investigates the photodetachment of the negative hydrogen ion H near an elastic wall in a magnetic field.The magnetic field confines the perpendicular motion of the electron,which results in a real three-dimensional well for the detached electron.The analytical formulas for the cross section of the photodetachment in the threedimensional quantum well are derived based on both the quantum approach and closed-orbit theory.The magnetic field and the elastic surface lead to two completely different modulations to the cross section of the photodetachment.The oscillation amplitude depends on the strength of the magnetic field,the ion-wall distance and the photon polarization as well.Specially,for the circularly polarized photon-induced photodetachment,the cross sections display a suppressed(E E th) 1/2 threshold law with energy E in the vicinity above Landau energy E th,contrasting with the(E E th) 1/2 threshold law in the presence of only the magnetic field.The semiclassical calculation fits the quantum result quite well,although there are still small deviations.The difference is attributed to the failure of semiclassical mechanics.     

High-order harmonic generation in a two-color strong laser field with Bohmian trajectory theory

We theoretically study the high-order harmonic generation(HHG) in a two-color laser field using the Bohmian mechanics. Our results show that, for the case of a weak second-color laser field, the simulation of the HHG with only one central Bohmian trajectory is in a good agreement with the ab initio time-dependent Schr o¨dinger equation(TDSE) results.In contrast, with the increase of the amplitude of the second-color laser field, the HHG spectra from the single central Bohmian trajectory deviate from the TDSE results more and more significantly. By analyzing the Bohmian trajectories,we find that the significant deviation is due to the fact that the central Bohmian trajectory leaves the core quickly in the two-color laser field with the breaking of inversion symmetry. Interestingly, we find that another Bohmian trajectory with different initial position, which keeps oscillating around the core, could qualitatively well reproduce the TDSE results. Furthermore, we study the HHG spectrum in a two-color laser field with inversion symmetry and find that the HHG spectrum in TDSE can be still well simulated with the central Bohmian trajectory. These results indicate that, similar to the case of one color laser field, the HHG spectra in a two-color laser field can be also reproduced with a single Bohmian trajectory,although the initial position of the trajectory is dependent on the symmetry of the laser field. Our work thus demonstrates that Bohmian trajectory theory can be used as a promising tool in investigating the HHG process in a two-color laser field.