Br2分子里德堡态的高分辨转动谱研究

用窄线宽（０．０８ｃｍ＾－＾１）脉冲可调谐紫外激光和（２＋１）多光子电离方法测量了Ｂｒ２的里德堡（Ｒｙｄｂｅｒｇ）态光谱,在７００００－７１５００ｃｍ＾－＾１范围内,获得了溴分子［П３／２］４ｄ振动系列,测量（ｖ＇,ｖ”）＝（１,０）,（２,０）的高分辨振转谱,得到其转动常数Ｂ’７９－８１分别为０．０８８３２和０．０８８０５ｃｍ＾－＾１,并提出此系列的角动量量子数Ω应为１。     

锂分子里德堡态和双激发态的重新分类

根据里德堡轨道的类氢nλ特性 ,对 7Li2 实验已观测到的和理论计算给出的 6 8个电子态进行了分类 ,把这些态划分为核实贯穿里德堡态和核实非贯穿里德堡态 .讨论了双电子激发态和里德堡态的微扰 ,也讨论了这种分类的意义     

钠分子1Πg里德堡态光谱研究

通过光学-光学双共振(OODR)光谱方法,研究了钠分子六个高激发1Πg态,对它们进行了振动和转动归属,获得了分子常数和势能曲线.根据里德堡轨道的nlλ特性,将1～101Πg态划分为实贯穿里德堡态和实非贯穿里z德堡态.     

钠分子^1Пg里德堡态光谱研究

通过光学－光学以共振（ＯＯＤＲ）光谱方法,研究了钠分子六个高激发＾１Пｇ态,对它们进行了振动和转动归属,获得了分子常数和势能曲线。根据里德堡轨道的ｎｌλ特性,将１－１０＾１Пｇ态划分为实贯穿里德堡态和实非贯穿里堡态。     

Na原子高里德堡态的辐射寿命

用可调谐激光两步激发Ｎａ原子高激发发里德堡态布居，在光激发后施加脉冲电场测量激发态的场电离阈，利用阈值电场和延迟场电离方法测定了ｎｓ（ｎ＝２０～２４）和ｎｄ（ｎ＝１９～２３）态的寿命值，并与计算值进行了比较，对影响寿命的因素作了讨论。     

锂分子3^1Ⅱg里德堡态的光谱研究

我们用脉冲光学-光学双共振荧光激发谱（OODR），测量了在35500-38000cm^-1能量范围内的里德堡态，观察到^7Li23^1Ⅱg态的10个振动能，本文观测的3^1Ⅱg态的146条激发谱线进行了归属，得到了新的Dunhm常数，RKR势能曲线以及A^1∑u^ 到3^1Ⅱg态跃迁的夫兰克-康登因子，并且讨论了3^1Ⅱg态的双重分裂以及与附近里德堡态F（4）^1∑g^ ,5^1∑g^ ,6^1∑g^ 和G（2）^1Ⅱg的微扰，发现在我们的实验精度下（0.2cm^-1)3^1Ⅱg态掇重分裂可以忽略。     

Br2偶宇称里德堡态的转动结构和电子角动量

由（２＋１）多光子电离方法获得溴分子６８８００－６９６００ｃｍ＾－１范围内的［ΠΠ／２］４ｄ偶宇称里德堡态转动激发光谱，通过对转动光谱的分析，确定了转动常数，Ｂ８１－８１＝０．０８６８８。并对电子角动量进行了标定，角动量Ω＝１。     

锂分子31Πg里德堡态的光谱研究

我们用脉冲光学-光学双共振荧光激发谱(OODR),测量了在35 500～38 000 cm-1能量范围内的里德堡态,观察到7Li231Πg态的10个振动能级.本文对观测的31Пg态的146条激发谱线进行了归属,得到了新的Dunham常数,RKR势能曲线以及A1Σ+u到31Πg态跃迁的夫兰克-康登因子,并且讨论了31Πg态的双重分裂以及与附近里德堡态F(4)1Σ+g,51Σ+g,61Σ+g和G(2)1Πg的微扰.发现在我们的实验精度下(0.2 cm-1) 31Πg态的双重分裂可以忽略.     

碱原子高里德堡态的极化率

本文使用一种具有解析解的原子唯象势模型,计算了碱原子Na,K,Rb,Cs里德堡(15≤n≤55)的标量和量极化率,计算结果与实验符合很好。还确定了极化率标度关系α=An^*7+Bn^*6中的系数A和B,由此关系外推所得结果也与实验很好地符合。 关键词：     

Role of rotational state-selected for nonadiabatic alignment: OCS molecules in femtosecond laser fields

Nonadiabatic alignment by intense nonresonant laser fields is a versatile technique to manipulate the spatial direction of molecules. By solving the time-dependent Schrödinger equation numerically the degree of alignment of the molecules initially in different rotational state are calculated and the results show that the degree of alignment strongly depends on the initial rotational state. Thus, the present study indicates that, for obtaining a high degree of alignment for molecules, appropriate selection of molecular rotational states is necessary.     

Rydberg excitation of neutral nitric oxide molecules in strong UV and near-IR laser fields

Rydberg state excitations of neutral nitric oxide molecules are studied in strong ultraviolet(UV) and near-infra-red(IR) laser fields using a linear time-of-flight(TOF) mass spectrometer with the pulsed electronic field ionization method.The yield of Rydberg molecules is measured as a function of laser intensity and ellipticity,and the results in UV laser fields are compared with those in near-IR laser fields.The present study provides the first experimental evidence of neutral Rydberg molecules surviving in a strong laser field.The results indicate that a rescattering-after-tunneling process is the main contribution to the formation of Rydberg molecules in strong near-IR laser fields,while multi-photon excitation may play an important role in the strong UV laser fields.     

Vortices in femtosecond laser fields

We experimentally generate optical vortices in the output beam of a 20-fs Ti:sapphire laser. Screw phase dislocations are imposed on the spectral components of the short pulses by aligning a computer-generated hologram in a dispersionless 4f setup.     

Enhanced ionization of vibrational hot carbon disulfide molecules in strong femtosecond laser fields

By using a heated molecular beam in combination with a time-of-flight mass spectrometer, we experimentally study the ionization of vibrational-hot carbon disulfide(CS_2) molecules irradiated by a linearly polarized 800-nm 50-fs strong laser field. The ion yields are measured in a laser intensity range of 7.0 × 10~(12) W/cm~2–1.5 × 10~(14) W/cm~2 at different molecular temperatures of up to 1400 K. Enhanced ionization yield is observed for vibrationally excited CS_2 molecules.The results show that the enhancement decreases as the laser intensity increases, and exhibits non-monotonical dependence on the molecular temperature. According to the calculated potential energy curves of the neutral and ionic electronic states of CS_2, as well as the theoretical models of molecular strong-field ionization available in the literature, we discuss the mechanism of the enhanced ionization of vibrational-hot molecules. It is indicated that the enhanced ionization could be attributed to both the reduced ionization potential with vibrational excitation and the Frank–Condon factors between the neutral and ionic electronic states. Our study paves the way to understanding the effect of nuclear motion on the strongfield ionization of molecules, which would give a further insight into theoretical and experimental investigations on the interaction of polyatomic molecules with strong laser fields.     

Kinetic energy release of diatomic and linear triatomic molecules in intense femtosecond laser fields

The kinetic energy release of fragment ions produced by the interaction of femtosecond laser pulse radiation with diatomic and linear triatomic molecules N_2, CO, CO_2 and CS_2 is investigated. In the case of linear polarization, angles at which the kinetic energy release of ions has the maximum value are different from the alignment of molecules though the kinetic energy release of fragment atomic ions depends on the angle between the laser polarization vector and the detection axis of the time-of-flight. For the diatomic molecules, the critical internuclear distance in multielectron dissociative ionization with a circularly polarized light is larger than that with a linearly polarized light. For linear triatomic molecules, our data indicate that a concerted Coulomb explosion process is a universal phenomenon in the interaction of molecules with intense laser fields, even in the circularly polarized regime. During two C－O (or C－S) bonds breaking simultaneously, the C ion obtained larger energy in circular polarization than that in the linear polarization. Different variations of kinetic energy release between the diatomic and the linear triatomic molecules are discussed.     

Rydberg molecules in external fields: a semiclassical analysis

We analyze the spectra of simple Rydberg molecules in static fields within the framework of closed/periodic-orbit theories. We conclude that in addition to the usual classical orbits one must consider classically forbidden diffractive paths. Further, the molecule brings in a new type of "inelastic" diffractive trajectory in addition to the usual "elastic" diffractive orbits encountered in systems with point scatterers. The relative importance of inelastic versus elastic diffraction is quantified by merging the usual closed orbit theory framework with molecular quantum defect theory.     

Timescales in the response of materials to femtosecond laser excitation

The interaction of ultrashort laser pulses with materials involves a number of special features that are different from laser–matter interaction for longer pulse durations. For femtosecond laser excitation the fundamental physical processes such as energy deposition, melting, and ablation are separated in time. By choosing proper time windows, the various processes can be investigated separately. We present selected examples of theoretical studies of free electron excitation in metals, timescales of different melting processes, and peculiarities of near-threshold ablation. Depending on the timescales and intensity ranges, the discussed processes are combined in an overall picture of possible pathways of the material from excitation to ablation. PACS 61.80.-x; 64.70.-p     

Muonic molecules in superintense laser fields

We study theoretically the ionization and dissociation of muonic molecular ions (e.g., dd mu) in superintense laser fields. We predict that the bond breaks by tunneling of the lightest ion through a bond-softened barrier at intensity I > or =10(21) W/cm(2). Ionization of the muonic atomic fragment occurs at much higher intensity I > or =6 x 10(22) W/cm(2). Since the field controls the ion trajectory after dissociation, it forces recollision of a approximately 10(5)-10(6) eV ion with the muonic atom. Recollision can trigger a nuclear reaction with sub-laser-cycle precision. In general, molecules can serve as precursors for laser control of nuclear processes.