ASYMMETRY PARAMETERS AND DIFFERENTIAL CROSS SECTIONS FOR PHOTOIONIZATION-EXCITATION OF HELIUM

Asymmetry parameter β₂ for photoionization of helium leaving the He⁺ ion in the n=2 level and differential cross sections(DCSs) in the n=2,3,4 levels with photon emission angle θ=90⁰ are provided at photon energies 69-76.8 eV employing the R-matrix method with a 20-term target representation, in which five polarization orbitals \bar{6}l are included. The asymmetry parameter β₂ and the DCS, in the n=2 level in the region of 69-73 eV, are in good agreement with available experimental and theoretical results. Above the n=3 threshold, we present new theoretical results along with measurements. No theoretical and experimental results can be used to compare with the present calculations of the DCSs for photoionization into the He⁺ ion in the n=3,4 levels.     

LASER-ASSISTED e-Ar SCATTERING IN CO2 LASER FIELD

Electron scattering from argon in a laser field is investigated empolying the second-order perturbation theory. The absolute differential cross sections of e-Ar scattering with multiphoton exchange in special scattering geometries G1 (for small-angle scattering) and G2 are calculated. Our results are found to be better than other theoretical results as compared with the experimental data.     

ASYMMETRY PARAMETERS AND DIFFERENTIAL CROSSSECTIONS FOR PHOTOIONIZATION-EXCITATION OF HELIUM

Asymmetry parameterβ2 for photoionization of helium leaving the He+ ion in the n = 2 level and differential cross sections(DCSs) in the n = 2, 3, 4 levels with photon emission angle θ=90°are provided at photon energies 69－76.8 eV employing the R-matrix method with a 20-term target representation, in which five polarization orbitals 6l are included. The asymmetry parameter β2 and the DCS, in the n=2 level in the region of 69－73eV, are in good agreement with available experimental and theoretical results. Above the n = 3 threshold, we present new theoretical results along with measurements. No theoretical and experimental results can be used to compare with the present calculations of the DCSs for photoionization into the He+ ion in the n = 3, 4 levels.     

电子被氩,氪,氙原子散射总截面的光学模型研究

文中基于光学模型势方法，详细分析并改进了一种准自由模型吸收势，把它作为光学模型的虚部，在能量０．１－３００ｅＶ的范围内计算了电子被Ａｒ，Ｋｒ，Ｘｅ原子散射的总截面，计算结果与实验值进行了比较。     

正,负电子被原子散射的光学势方法—e^±—Na散射总截面的计算

将原子核散射理论中的光学势方法应用于正、负电子被原子散射的计算，提出了不含任意参数的光学势以及由此确定散射矩阵元的方法，计算了低能（≤５０ｅＶ）正、负电子被Ｎａ散射的总截面并与实验结果进行了比较。     

Observation of photon recoil effects in single-beam absorption spectroscopy with an ultracold strontium gas

We report on observing photon recoil effects in the absorption of a single monochromatic light at 689 nm through an ultracold ⁸⁸Sr gas,where the recoil frequency is comparable to natural linewidth of the narrow-line transition 5s^{2 1}S₀-5s5p ³P₁ in strontium.In the regime of high-saturation,the absorption profile becomes asymmetric due to the photon-recoil shift,which is of the same order as the natural linewidth.The lineshape is described by an extension of the optical Bloch equations including the momentum transfers to atoms during emission and absorption of photons.Our work reveals the photon recoil effects in a simplest single-beam absorption setting,which is of significant relevance to other applications such as saturation spectroscopy,Ramsey interferometry,and absorption imaging.     

Rabi Oscillations and Coherence Dynamics in Terahertz Streaking-Assisted Photoelectron Spectrum

We present an approach,a Terahertz streaking-assisted photoelectron spectrum(THz SAPS),to achieve direct observations of ultrafast coherence dynamics with timescales beyond the pulse duration.Using a 24 fs probe pulse,the THz SAPS enables us to well visualize Rabi oscillations of 11.76 fs and quantum beats of 2.62 fs between the 5S_1/2 and 5P_3/2 in rubidium atoms.The numerical results show that the THz SAPS can simultaneously achieve high resolution in both frequency and time domains without the limitation of Heisenberg uncertainty of the probe pulse.The long probe pulse promises sufficiently high frequency resolution in photoelectron spectroscopy allowing to observe Autler-Townes splittings,whereas the streaking THz field enhances temporal resolution for not only Rabi oscillations but also quantum beats between the ground and excited states.The THz SAPS demonstrates a potential applicability for observation and manipulation of ultrafast coherence processes in frequency and time domains.     

时间戳相机中心算法和解离电子/离子动量分布仿真

模拟仿真了速度成像谱仪中解离电子/离子飞行运动轨迹,获得电子/离子动量三维分布的真实图像,针对时间戳相机Tpx3Cam在动量分布探测成像中存在的团簇效应问题,发展了适用于高计数率情况下的中心算法。仿真结果显示,提出的中心算法可以减少约一个数量级的数据容量,并让单像素位置精度提高到0.1像素,实现了粒子动量分布的超分辨位置成像。模拟ns态电子电离和N₂分子(1,1)通道库伦爆炸实验,发现中心算法能够使电子平行于探测器平面的动量分辨提升30%;使库伦爆炸产生的N⁺飞行时间谱分辨提升80%。同时,在具有背景气体干扰情况下,对CO分子库伦爆炸产物离子进行半径协方差分析,提出的中心算法成功观测到C⁺和O⁺的关联。     

激光辅助电子-He原子散射 --一种特殊情况下的微分截面的计算

利用二阶微扰论的方法计算了动量转移与激光场的偏振方向垂直条件下,电子－Ｈｅ原子碰撞的自由－自由跃迁的单光子和两光子交换的微分截面,结果与最近的实验结果符合得很好。