Pure multi-photon ionization of the ground 1S and metastable 2S state of the hydrogen atom with plane-polarized light of threshold frequency

Formulas for N-photon ionization of the hydrogen atom states 1S and 2S with plane-polarized light at the threshold frequency $\text{ω=}\text{I}\text{N}\text{h}\text{?}$ (I ionization energy) are proposed and shown to reduce in the one-photon case to the well-known Stobbe expressions.     

Influence of multi-photon excitation on the atomic above-threshold ionization

Using the time-dependent pseudo-spectral scheme, we solve the time-dependent Schr ¨odinger equation of a hydrogenlike atom in a strong laser field in momentum space. The intensity-resolved photoelectron energy spectrum in abovethreshold ionization is obtained and further analyzed. We find that with the increase of the laser intensity, the abovethreshold ionization emission spectrum exhibits periodic resonance structure. By analyzing the population of atomic bound states, we find that it is the multi-photon excitation of bound state that leads to the occurrence of this phenomenon, which is in fairly good agreement with the experimental results.     

等离子体密度对多光子电离的影响

利用“光学度规”的方法研究了等离子体中的多光子电离,获得了“弯曲时空”中的量子Volkov态.应用量子电动力学的形式散射理论得出了多光子电离的散射截面.阐述了等离子体密度对发生在其中的多光子电离的“抑制”作用 关键词： 多光子电离 激光等离子体     

Effect of two-level atom on photon packet polarization

A packet of photons interacting with a two-level atom is considered. It is shown that if the atomic dipole momentum transition vector is not parallel to the photon polarization, the linear photon polarization changes into an elliptical one. The upper-bound estimation for the ratio of short and long axes of the ellipse gives 0.2. The phenomenon is of a quantum origin and caused by the action of the atom on the photon packet.     

用屏蔽法计算较轻元素原子的高次电离能

考虑到离子的相对论效应,依据屏蔽方法,给出了原子第2、1壳层电子电离能的一种表达式.依据较轻元素原子低次(小于13)电离能实验数据,总结出原子(离子)电离第2、1壳层不同电子态电子时,相应的屏蔽系数与电子态及原子序数的函数关系,根据该函数关系,可求出相应原子的高次电离电子的屏蔽系数.计算了原子序数13至23的元素高电荷态离子基态电离能,计算结果与文献可提供的实验数据相符合.     

光的偏振对热光关联成像的影响

根据完全偏振光的不同偏振态和部分偏振光的不同偏振度对二阶关联函数的影响,利用统计光学理论研究了光的不同偏振性质对关联成像的可见度和信噪比的影响.研究表明,光的偏振对热光关联成像的影响体现在部分偏振光的不同偏振度上,关联成像的可见度是偏振度的二次函数,由二阶关联函数方法得到的信噪比随着偏振度增大而提高,而利用减去背景项的二阶关联函数以及二阶相干度方法得到的信噪比均与偏振度无关. 关键词： 关联成像 偏振 可见度 信噪比     

Three-photon ionization of the potassium atom by linearly and circularly polarized light

The measurement and calculation results of the dependence of the three-photon ionization process of potassium atoms by linearly and circularly polarized light within the frequencies from 16300 to 16600 cm^-1 are presented. The experimental data do not confirm the predictions of perturbation theory on the existence of a window of nonlinear transparency for circularly polarized light.     

Dependence of the process of nonlinear two-electron ionization of the barium atom on the polarization of the laser radiation

Experimental results are presented on measuring the yield of Ba²⁺-ions versus polarization of neodymium—glass laser radiation. These results show that the resonance in the Ba²⁺ ion yield occurs with the bound two-electron state rather than with the autoionization state in the Ba-atom spectrum.     

Effect of polarization spectroscopy in multitep excitation and ionization of atoms on ionization efficiency

In this peper, the seventeen real motion equation of atoms were shown for the first time inconsiderlng the polarization choices of laser lights. The importance of polarization spectrcoscopy in thedetermination of ionization yields of multi-step excitation and ionization of atoms (MSEIA) wasshown.     

532nm丙酮和丁酮多光子电离解离研究

利用激光质谱法,通过分析丙酮和丁酮的多光子电离飞行时间质谱,对其532nm多光子电离机制进行了研究. 结果发现丙酮相干吸收若干光子跃迁到高能超激发态,再继续吸收光子产生各种碎片离子,而丁酮先解离后电离. 两质谱中都有质荷比为4、6、8的离子,原则上是高价离子,但在相似条件下未见相关报道,因此对离子出险原因及确认尚待进一步研究. 实验中丁酮发生异构现象,其异构体电离解离出较强的C2H3O+(m/e=43).丙酮没有相关离子产生.     

Reduction of multi-photon ionization in dielectrics due to collisions

The collisional effect due to the multi-photon ionization process in dielectric material has been studied. We found that the breakdown threshold of fused silica is the same for both linearly and circularly polarized light at 55 fs and 100 fs, which we believe is an indication of the suppression of multi-photon ionization in solids. By numerically solving the time-dependent Schrödinger equation with scattering, for the first time, we have observed substantial reduction of the multi-photon ionization rate in dielectrics due to collisions.     

Effect of the emitter temperature and emitter atom ionization potential on field evaporation

The field evaporation of nickel, nichrome alloy, and tungsten carbide at different temperatures is studied with a time-of-flight atomic probe and a field emission microscope. The charge of evaporating ions does not depend on the emitter temperature: it decreases with decreasing evaporating field F _ev. If F _ev does not vary with temperature, so does the charge of the ions. In the case of multicomponent emitters with different ionization potentials of the components, the components evaporate at the same values of F _ev in the form of atoms and ionized clusters. The reason for such behavior is that the initial evaporation of the easily ionizable component decreases the binding energy of harder-to-ionize ones to the point where they can evaporate at the same field.     

运动原子多光子J-C模型中的熵交换与纠缠

考虑一个运动的二能级原子与单模热光场经由多光子过程相互作用, 利用量子约化熵理论研究原子与场之间的熵交换、用Concurrence量度原子与场之间的纠缠, 讨论原子初态、原子运动、热场平均光子数以及跃迁光子数对熵交换和纠缠的影响. 结果表明: 考虑原子运动时, 原子和光场熵变呈现周期性, 且发生熵交换现象; 与热光场的相互作用导致运动原子与场纠缠, 多光子过程有利于纠缠加强. 在原子和光场熵变均为零处, 纠缠也为零.     

Resonance enhanced multi-photon ionization of neutral atoms sputtered with Ga-FIB

Resonance enhanced multi-photon ionization (REMPI) of neutral aluminum atoms sputtered with gallium focused ion beam (Ga-FIB) was studied in terms of substrate temperature and chemical state of the surfaces. Aluminum has the lowest excitation state (3p ²P_3/2) at 112 cm⁻¹ above the ground state (3p ²P_1/2). The results showed that the total REMPI signal intensity of neutral aluminum atoms and the ratio of REMPI signal intensities attributed to ²P_1/2 to ²P_3/2 were increased at higher temperature. On the other hand, the REMPI signal and the ratio were decreased in the case of partially oxidized aluminum surfaces. Considering the result on Al₂O₃, it was confirmed that the REMPI signals of ground state ²P_1/2 and the first excited spate ²P_1/2 could be affected with surface oxidation state.     

Selection rules for atom multiphoton ionization by intense light in a non-perturbative theory

Using a non-pertubative theoretical analysis we establish the selection rules for the multiphoton ionization effect in hydrogen-like atoms by intense linearly and circularly polarized light, alternatively. No approximations are carried out during these calculations and the obtained results are more general than those obtained to date.     

The spectrum of above-threshold electrons produced upon atom ionization by a short light pulse

The Landau-Dykhne approximation for the spectrum of above-threshold electrons produced upon ionization of atoms by a monochromatic laser field is used to calculate the spectrum in the case of ionization by a short laser pulse. The spectra obtained in this way are compared with those calculated by the adiabatic theory. The comparison shows that the Landau-Dykhne approximation with the properly chosen exponential factor describes well the averaged spectrum.     

Effect of laser polarization on strong-field ionization andfragmentation of nitrous oxide molecules

Ionization of molecules in femtosecond laser fields is the most fundamental and important step of various strong-field physical processes. In this study, we experimentally investigate strong field ionization of linear N_2O molecules using a time-of-flight mass spectrometer in 800-nm laser fields. Yields of the parent ion and different fragment ions are measured as a function of laser intensity in the range of 2.0×10~(13) W/cm~2 to 3.6×10~(14) W/cm~2. We also investigate the dependence of strong field ionization and dissociation of N_2O on laser ellipticity and polarization direction. The significant role of laser induced electron re-collision in the formation of highly charged fragment ions is proved. The physical mechanism of strong field ionization and fragmentation is discussed, based on our experimental results.