Enhancement of High-Order Harmonic Emission and Isolated 7-as Pulse Generation with Rydberg Atoms by Using a Two-Color Laser Field

An efficient method to enhance the harmonic efficiency and generate an isolated attosecond pulse is proposed by preparing the initial state as a coherent superposition of the ground state and a Rydberg state in a two-color laser field. By numerically solving the time-dependent Schrödinger equation, we found that for the superposition state with the optimal Rydberg state, not only is the harmonic efficiency enhanced significantly, but also the width of the continuous spectrum is extended. The ionization probability and the time-frequency distribution of the harmonic spectrum are also calculated to understand the physical origin of the enhancement of the harmonic spectrum. In addition, by adjusting the parameter of the laser pulse, a supercontinuum with both higher conversion efficiency and slighter modulation can be observed. As a result, an isolated 7-as pulse with a bandwidth of 495 eV can be obtained after phase compensation.     

Crossed Beam Study on the F+D2→DF+D Reaction at Hyperthermal Collision Energy of 23.84 kJ/mol

We presented an experimental apparatus combining the H-atom Rydberg tagging time-of-flight technique and the laser detonation source for studying crossed beam reactions athyperthermal collision energies. The preliminary study of the F+D₂→DF+D reaction at hyperthermal collision energy of 23.84 kJ/mol was performed. Two beam sources were used in this study: one is the hyperthermal F beam source produced by a laser detonation process, and the other is D₂ beam source generated by liquid-N₂ cooled pulsed valve. Vibrational state-resolved di erential cross sections (DCSs) of product for the title reaction were determined. From the product vibrational state-resolved DCS, it can be concluded that products DF(v'=0, 1, 2, 3) are predominantly distributed in the sideway and backward scattering directions at this collision energy. However, the highest vibrational excited product DF(v'=4), is clearly peaked in the forward direction. The probable dynamical origins for these forward scattering products were analyzed and discussed.     

NO2分子的光学-光学双色双共振多光子离化谱

以Nd:YAG激光器的二倍频输出光为抽运光,其三倍频输出抽运的光学参量发生/放大器输出光为探测光,利用光学-光学双色双共振多光子离化光谱技术(OODR-MPI),获得了NO₂分子在605—675nm探测光波长范围内的多光子离化激发谱. 通过对NO₂分子离化机理的分析,确定了在此波长区间,NO₂分子经1+3+1双共振多光子过程离化,离化通道为NO₂(X²A₁)hν 关键词： 2')" href="#">NO₂ 光学-光学双共振多光子离化谱 里德伯态 分子常数     

里德伯原子向超冷等离子体的自发转化

在铯原子MOT中,利用三光子激发冷原子获得超冷里德伯原子,改变里德伯原子间的相互作用时间,获得超冷等离子体的信号.研究了里德伯原子向超冷等离子体的自发转化过程和里德伯原子的初始电离机理. 关键词： 里德伯原子 相互作用 等离子体 电离机理     

Efficient Generation of Atomic Singlet State with Rydberg Blockade and Lie-Transform-Based Pulse Design

A protocol to generate atomic singlet state of three atoms is proposed. The strong Rydberg interactions between atoms mediate the multi-qubit operations and help to simplify the dynamics of the system. The effective Hamiltonian is constructed in the regime of Rydberg blockade and the evolution path is built up from an initial state to the target singlet state via the Lie-transform-based pulse design. Numerical simulations show the protocol can produce atomic singlet state with high fidelity and holds robustness against several types of experimental imperfections. Therefore, it may provide some useful results for the generation of singlet states in atomic system.     

On phase-coherence in rescattering in multiphoton ionization and in higher-order harmonic generation

Summary  The recently discovered plateau and rings in high-order multiphoton ionization apparently have their origin in rescattering. Similarly, rescattering is involved in higher-order harmonic generation. Using a simple one-dimensional model, it is shown that the phase-coherence in this rescattering process is of considerable importance. The authors of this paper have agreed to not receive the proofs for correction. This work has been supported by the East-West Program of the Austrian Academy of Sciences and by the Austrian Ministry of Science and Transportation under project no. 45.372/2-IV/6/97. One of us (JZK) acknowledges the support of the Polish Committee of Scientific Research (grant KBN 2 P03B 007 13).     

Full configuration interaction calculation of the low lying valence and Rydberg states of BeH

The all-electron full configuration interaction (FCI) vertical excitation energies for some low lying valence and Rydberg excited states of BeH are presented in this article. A basis set of valence atomic natural orbitals has been augmented with a series of Rydberg orbitals that have been generated as centered onto the Be atom. The resulting basis set can be described as 4s2p1d/2s1p (Be/H) + 4s4p3d. It allows to calculate Rydberg states up to n= {3,4,5} of the s, p, and d series of Rydberg states. The FCI vertical ionization potential for the same basis set and geometry amounts to 8.298 eV. Other properties such as FCI electric dipole and quadrupole moments and FCI transition dipole and quadrupole moments have also been calculated. The results provide a set of benchmark values for energies, wave functions, properties, and transition properties for the five electron BeH molecule. Most of the states have large multiconfigurational character in spite of their essentially single excited nature and a number of them present an important Rydberg-valence mixing that is achieved through the mixed nature of the particle MO of the single excitations.     

汞原子6sns 3S1,6snd 3D1 Rydberg系列的寿命

利用多通道量子数亏损理论计算了汞原子6sns^3S1(n=11～25),6snd^3D1(n=12～24)两个Rydberg系列的能级和寿命,给出了这两个系列寿命所遵循的公式,6sns^3S。系列为r=0．814v^2.835(ns),6snd^3D1系列为r=0．302v^2.926ns),其中v为有效量子数。     

经验势能函数的改进

本文提出改进经验势能函数的一般方法,即构成改进后的势能函数V=WV′,校正函数W=exp{P[(γ_e/γ)^q-1]}。此法应用于改进Rydberg函数与PG函数,结果成功。     

Classical study of and collisions in intense laser fields

In this paper, ion-atom and ion-ion collisions in the presence of intense laser fields are qualitatively studied by Classical Trajectory Monte Carlo (CTMC) simulations. It is found that in contrast to the field-free collisions, the colliding ion and the target nucleus could absorb energy from the applied laser fields when the electrons escape from the collision system. This result is explained in terms of Coulomb explosion induced by the enhanced ionization at the so-called critical internuclear distance. Also, the corresponding energy gain cross-sections are evaluated. Received: 7 October 1998 / Received in final form: 28 January 1999