强激光场中对称三原子分子多光子振动激发的动力学李代数计算

用分子的内坐标给出的动能加上用动力学代数方法给出的用内坐标表示的分子势能得出对称三原子分子的总的能量表达式,给出了时间演化算子并计算了对称三原子分子在强激光场中振动激发。作为例子,计算了H2O分子在频率 的激光场中的激发,通过讨论可以发现H2O在激光场中的跃迁几率随时间的变化是周期性的,水分子从激光场中吸收的能量由吸收的平均光子数确定,被吸收的平均光子数随时间的变化也是周期性的。     

线型三原子分子在强激光场中多光子激发的李代数方法

使用二次非谐振子模型和Magnus近似方法构造了在强激光场下线型三原子分子的振动哈密顿并推导出时间演化算符的代数形式,在此基础上研究了线型DCN分子的跃迁几率随外场的频率和强度的变化关系,表明了多光子跃迁谱的特点.     

强激光场中双原子分子多光子激发的李代数方法

用“模拟势－李代数”方法研究了双原子分子在强激光场中的多光子振动激发，计算了跃迁几率与外场频率、时间的关系，讨论了有两个激光场时跃迁儿率所受的影响． 关键词：     

线性三原子分子振动激发控制的李代数方法

采用李代数方法研究线性三原子分子在强红外激光场中的多光子激发及其控制,实现了态选择激发,并讨论了激光脉冲对控制的影响. 关键词： 多光子 李代数 激光     

一维三原子分子的振动

考虑三原子分子的振动问题,利用线性代数的化标准型理论,获得该振动系统简正频率的数学表达式,并讨论了几种特殊的情况.     

用李代数方法解析研究线性三原子分子振动的动力学纠缠

采用李代数方法研究了线性三原子分子非线性伸缩振动的动力学纠缠,给出了描述纠缠行为的线性熵和冯诺伊曼熵的解析表达式,并分别讨论了初态为Fock态和相干态下的HCN和DCN分子伸缩振动纠缠的动力学性质.     

用李代数方法研究强激光场中双原子分子的多光子激发

组成系统哈密顿量的一组算子对易关系封闭,构成一个李代数.这组算子的统计平均值随时间的演化满足一个封闭的一阶线性微分方程组.讨论了有关物理量的统计平均值随时间的变化关系.     

非线型三原子分子势能面的Lie代数方法

利用Lie代数方法得到三原子分子的代数Hamiltonian ,通过对光谱数据的拟合确定其展开系数 ,再用相干态得到代数Hamiltonian的经典极限 ,从而得到三原子分子的势能面 .以H2 O分子为例进行了计算 ,其理论值与实验结果一致. The algebraic Hamiltonian for a triatomic molecule can be obtained by using dynamical Lie algebra method (the expansion coefficients are obtained by fitting spectroscopic data). Triatomic molecular potential energy surface (PES) is obtained by using coherent state to take the classical limits of algebraic Hamiltonian. This PES is applied to H 2O molecule, and the deduced force constant is in good agreement with the experimental data.     

动力学对称群方法对三原子分子高激发振动态的理论研究

利用动力学对称群方法研究了弯曲三原子分子的振动高激发态能谱-该方法显示：三原子分子的动力学对称性为U₁(4)U₂(4),则三原子分子的Hamiltonian量可写成代数的各元素之和,通过李代数处理而求得分子代数Hamiltonian量的本征值,进而得到分子的振动能谱-并具体计算了O₃分子- 关键词：     

臭氧分子在激光场中的多光子激发

采用二次量子化方法和酉变换讨论了O3 分子在激光场中的多光子激发 .推导出了O3 分子的振动Hamiltonian算子、从基态到各激发态的跃迁几率公式 ,以及O3 分子从激光场中吸收的光子数公式 ,并分析了计算结果 .这包括对O3 分子伸缩振动能谱的计算及与实验结果的比较 ,跃迁几率随外场频率的变化、随时间的变化 ,以及O3 分子在辐射场中的能量吸收情况 (取光场强度为 5× 10 -2 W /cm2 ) .建立讨论所有具有C2v对称分子从基态到第四激发态以下各态多光子激发问题的模型     

异核双原子和三原子分子在红外强激光场中的电离抑制

Ionization is the fundamental process in interaction of atoms/molecules with femtosecond strong laser fields. Comparing to atoms, molecules exhibit peculiar behaviors in strong-field ionization because of their diverse geometric structures, molecular electronic orbitals as well as extra nuclear degrees of freedom. In this study, we investigate strong field single and double ionization of carbon monoxide (CO) and carbon dioxide (CO₂) in linearly polarized 50-fs, 800-nm laser fields with peak intensity in the range of 2×10¹³ W/cm² to 2×10¹⁴ W/cm² using time-of-flight mass spectrometer. By comparing the ionization yields with that of the companion atom krypton (Kr), which has similar ionization potential to the molecules, we investigate the effect of molecular electronic orbitals on the strong-field ionization. The results show that comparing to Kr, no significant suppression is observed in single ionization of both molecules and in non-sequential double ionization (NSDI) of CO, while the NSDI probability of CO₂ is strongly suppressed. Based on our results and previous studies on homonuclear diatomic molecules (N₂ and O₂), the mechanism of different suppression effect is discussed. It is indicated that the different structure of the highest occupied molecular orbitals of CO and CO₂ leads to distinct behaviors in two-center interference by the electronic wave-packet and angular distributions of the ionized electrons, resulting in different suppression effect in strong-field ionization.     

Multiphoton Ionization of Potassium Atoms in Femtosecond Laser Fields

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.     

强激光中原子过程的理论研究

从理论角度结合实际工作,概要地介绍强激光中原子过程的特点、理论研究现状及其在激光核聚变中的可能作用． A most important feature of atomic processes in laser fusion is pointed out. The current situation of theoretical study of these processes is analyzed, then. The possible application of the theoretical study is described by a illustrative example.All of the above mentioned things are based on our practical work.     

Transient Absorption of Organic Molecules under High-Power Laser Excitation

In the present work, results of investigations into the transient absorption of some organic compounds by the method of pulsed flash photolysis are given. Experimental investigations were carried out using an original setup of pulsed flash photolysis with an exciting pulse of XeCl-laser radiation of nanosecond duration and sensing by broadband laser-transient fluorescent radiation of a mixture of organic fluorophors called “white light” excited by the same source in the wavelength range 330–750 nm. The setup registers the short-living (singlet-singlet) and long-living (triplet-triplet) absorptions. The transient absorption spectra of already investigated para-terphenyl, naphthalene, and 1-phenyl-2(2-naphthyl)-ethylene molecules are presented; the spectra of the transient absorption and its nature are in good agreement with the experimental and calculated data published in the literature. We first investigated the transient absorption of LOC1 (S₁-S_n at 580 nm and T₁-T_n at 500 nm) and phenalemine 512 (S₁-S_n at 395 nm). It is demonstrated that the experimentally observed induced absorption of phenalemine 512 and PD 789 is the S₁-S_n absorption, which is in good agreement with the results of quantum-chemical calculations. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 12–16, September, 2005.     

Resonant Acceleration of Electrons in Combined Self-Consistent Quasistatic Electromagnetic Fields and Intense Laser Fields

Using the single electron model, the acceleration of electrons in combined circularly polarized intense laser fields and the spontaneous quasistatic fields （including axial and azimuthal magnetic fields, the axial and transverse electric fields） produced in intense laser plasma interaction is investigated analytically and numerically by fitting the proper parameters of the quasistatic fields based on the data from the experiment and numerical calculation. A new resonant condition is given. It is found that the resonance acceleration of electron depends not only on laser field, but also on the bounce frequency oscillating in the quasistatic magnetic field and electric field. The net energy gained by electron does not increase monotonously with axial electric field, but there are some optimal axial electric fields.     

Neutral Dissociation of Superexcited Nitric Oxide Induced by Intense Laser Fields

利用波长800 nm、脉宽60 fs、强度0.2 PW/cm²的强激光激发NO分子,随后通过荧光光谱检测到了处于激发态的N和O的中性碎片. 说明强激光导致的多光子激发同样可以引起NO分子的超激发,并且发生中性解离. 采用离子实解离模型,建立了NO分子的超激发态势能曲线. 提出了直接解离和预解离两种解离过程,分别对应生成N^*+O或O^*+N两个通道.     

Double Ionization Dynamics of Molecular Hydrogen in Ultrashort Intense Laser Fields

We experimentally investigate the double ionization of molecular hydrogen subjected to ultrashort intense laser pulses.The total kinetic energy release of the two coincident H~+ ions,which provides a diagnosis of different processes to double ionization of H_2,is measured for two different pulse durations,i.e.,25 and 5fs,and various laser intensities.It is found that,for the long pulse duration(i.e.,25 fs),the double ionization occurs mainly via two processes,i.e.,the charge resonance enhanced ionization and recollision-induced double ionization.Moreover,the contributions from these two processes can be significantly modulated by changing the laser intensity.In contrast,for a few-cycle pulse of 5fs,only the recollsion-induced double ionization survives,and in particular,this process could be solely induced by the first-return recollision at appropriate laser intensities,providing an efficient way to probe the sub-laser-cycle molecular dynamics.     

Simulation of Electron Temperature in Argon Clusters Subjected to Intense Laser Fields

Argon clusters subjected to intense femtosecond laser pulses are ionized by the optical fields and inelastic electron-ion collisions. The cluster plasmas absorb the laser energy through collisional inverse bremsstrahlung, leading the argon cluster plasmas to very hot states. The calculated electron temperature in the clusters indicates that the intense laser-cluster interactions are more energetic than interactions with molecules.