Multiple recapture of electrons in multiple ionization of the argon dimer by a strong laser field

We observe multiply frustrated tunneling ionization-induced dissociation of the argon dimers by intense linearly polarized ultrashort laser pulses. By measuring the kinetic energy release and angular distribution of the Coulomb explosion of up to eightfold ionized argon dimers, we can trace the recapture of up to two electrons to Rydberg states of the highly charged compound at the end of the laser pulse. Upon dissociation of the dimer, the Rydberg electron prefers to localize at the atomic ion with the higher charge state. We probe the electron recapture dynamics by a time-delayed weak pulse.     

PHOTOEXCITATION OF ATOM WITH ULTRASHORT LASER PULSES

The uncoupled basis set is used to describe the interaction between the ultrashort pulses and the Na atom. Several polarization configurations of laser pulses have been investigated, which produce different effects on the two-step photoexcitation process. The study shows that the final states of the transitions driven by ultrashort laser pulses have a strong dependence on the laser polarization configuration. A comparison of the two different basis sets shows that the uncoupled basis set may provide more information than the coupled basis set, such as angular distribution of the atom in the final states of the transitions.     

Inelastic processes in the interaction of an atom with an ultrashort electromagnetic pulse

Electron transitions occurring during the interaction of a heavy relativistic atom with a spatially inhomogeneous ultrashort electromagnetic pulse are considered by solving the Dirac equation. The corresponding transition probabilities are expressed in terms of known inelastic atomic form factors, which are widely used in the theory of relativistic collisions between charged particles and atoms. By way of example, the inelastic processes accompanying the interaction of ultrashort pulses with hydrogen-like atoms are considered. The probabilities of ionization and production of a bound-free electron-positron pair on a bare nucleus, which are accompanied by the formation of a hydrogen-like atom in the final state and a positron in the continuum, are calculated. The developed technique makes it possible to take into account exactly not only the spatial inhomogeneity of an ultrashort electromagnetic pulse, but also the magnetic interaction.     

Spectra induced by interactions of atoms with ultrashort electromagnetic pulses

An ultrashort pulse of an electromagnetic field incident on an atom shakes the atom and gives rise to various electron transitions in it. These processes are accompanied by the reemission of the incident ultrashort pulse. This paper studies the relation between the spectra of reemitted photons of an ultrashort pulse and the transitions of atomic electrons into particular states. The obtained partial reemission spectra can allow one to relate direction patterns to the probability of the excitation of an atom into different states.     

Synchronization of atomic quantum transitions by light pulses

The synchronization of atomic quantum transitions with natural Raman oscillations by ultrashort light pulses has been investigated. This phenomenon may be observed if the duration of the perturbation pulse is less than the period of oscillations of the forbidden atomic transitions. The accuracy of the direct measurements of the quantum transition times for trapped particles can be of the same order as the ratio of the two-photon transition frequency to the homogeneous line width.     

Influence of atomic densities on propagation property for ultrashort pulses in a two-level medium

The influence of atomic densities on the propagation property for ultrashort pulses in a two-level atom (TLA) medium is investigated. With higher atomic densities, the self-induced transparency (SIT) cannot be recovered even for 2π ultrashort pulses. New features such as pulse splitting, red-shift and blue-shift of the corresponding spectra arise, and the component of central frequency gradually disappears.     

Electron transitions and the spectrum of radiation emitted by an atom interacting with an ultrashort electromagnetic pulse

Electron transitions and the spectrum of radiation emitted by an atom interacting with an ultrashort electromagnetic pulse are studied based on the sudden perturbation approximation. The excitation and ionization probabilities, the spectra of pulse reradiation by the atom, and the reradiation cross sections are calculated. It is concluded that the reradiation of ultrashort electromagnetic pulses by multielectron atoms is of a coherent nature.     

Modified optical bloch equations in nonlocal systems of two-level atoms interacting with ultrashort light pulses

Modified optical Bloch equations for two-level atoms in the radiation field with the complex polarization vector, the complex amplitude, and the complex wave vector are derived. A specific case is considered in which a field of this kind acts on a separate atom of a nonlocal atomic system. The solution of the modified equations for the interaction of atoms with ultrashort light pulses is obtained.     

Scattering of an ultrashort electromagnetic radiation pulse by an atom in a broad spectral range

The scattering of an ultrashort electromagnetic pulse by atomic particles is described using a consistent quantum-mechanical approach taking into account excitation of a target and nondipole electromagnetic interaction, which is valid in a broad spectral range. This approach is applied to the scattering of single- and few-cycle pulses by a multielectron atom and a hydrogen atom. Scattering spectra are obtained for ultrashort pulses of different durations. The relative contribution of “elastic” scattering of a single-cycle pulse by a hydrogen atom is studied in the high-frequency limit as a function of the carrier frequency and scattering angle.     

Quantum state swap for two trapped Rydberg atoms

The quantum swap gate is one of the most useful gates for quantum computation. Two-qubit entanglement and a controlled-NOT quantum gate in a neutral Rydberg atom system have been achieved in recent experiments. It is therefore very interesting to propose a scheme here for swapping a quantum state between two trapped neutral atoms via the Rydberg blockade mechanism. The atoms interact with a sequence of laser pulses without individual addressing. The errors of the swap gate due to imprecision of pulse length, finite Rydberg interaction, and atomic spontaneous emission are discussed.     

Tomography vs quantum control for a three-level atom

We investigate the possibilities of controlling and reconstructing the state of a single three-level atom. We propose a physical scheme where information about the atomic state is extracted by measuring the total number of excitations after successive application of electromagnetic field pulses. We show that, in the non-degenerate case (different transition frequencies for different atomic transitions), a three-level atom is completely controllable and its state can be completely reconstructed. In the degenerate case (when both atomic transitions are identical), we consider two dynamically inequivalent configurations, Λ and Ξ. In this case, we show that the density matrix can always be completely reconstructed whereas their respective system cannot be completely controlled. We explain why this last incompatibility between control and tomography arises.     

Emission of an atom during its interaction with an ultrashort pulse of electromagnetic field

The electronic transitions and emission of an atom during its interaction with a spatially inhomogeneous ultrashort pulse of electromagnetic field are considered. The probabilities of excitation and ionization, as well as the spectra and cross sections of reemission of such a pulse by the atom, are obtained. As an example, the one-and two-electron inelastic processes accompanying the interaction of ultrashort pulses with hydrogen-and helium-like atoms are considered.     

The positronium atom as a benchmark for Rydberg excitation experiments in atomic physics

Positronium is a hydrogen-like pure leptonic atom that has gained great attention in basic physics for its role in antimatter studies, in quantum electrodynamics tests and in material science. Positronium spectroscopy is also an interesting research field, especially in the again unexplored region of Rydberg states, where motional effects turns out of overwhelming importance in determining the level structure, at variance with the usual Rydberg atomic spectroscopy. In this paper we present a simple theory of optical excitation of positronium high-n levels in strong magnetic fields, and determine the conditions for obtaining saturation of the transitions. It is shown that positronium atom can be an atomic physics benchmark for laser excitation experiments on Rydberg states in magnetic environments.     

超短脉冲激光与钾原子的相互作用

采有耦合和非耦合表象,描述了超短脉冲激光与钾原子的相互作用。分析了进一步 激发光电离的过程,导出了跃迁终态随激光偏振组合的密切关键。     

Mode-locked lasers and ultrashort light pulses

This article reviews some aspects of the generation of very short optical pulses using mode-locked lasers, with the emphasis laid on pulsed laser systems. Active and passive mode-locking is discussed, and the problem of measuring ultrashort light pulses is considered. A survey of some commonly used sources and techniques for the generation of ultrashort light pulses follows. The paper concludes with a short account of limitations in the generation and propagation of these pulses.     

Rabi frequency and optical Bloch equations for a short femtosecond optical pulse

We investigate the interaction of a multilevel atom with a short femtosecond optical pulse beyond the scope of the rotating-wave approximation. We consider the behavior of a three-level atom under the action of two optical pulses resonant with two allowed transitions and a two-level atom under the action of a resonant optical pulse. It is shown that the imaginary part of the off-diagonal elements of the density matrix oscillates with high frequency due to the counter-rotating terms. It is shown also that an effective time-dependent addition to the Rabi frequency exists, which is of importance for ultrashort optical pulses.     

Photoelectron angular distributions from strong-field coherent electronic excitation

Photoelectron Angular Distributions (PADs) resulting from nonperturbative excitation of potassium atoms using shaped femtosecond laser pulses are presented. We study control exerted by (1) the polarization of an unshaped, i.e., a bandwidth-limited light pulse, (2) shaped linearly polarized light, and (3) a combination of both degrees of freedom, i.e., polarization-shaped laser pulses. A theoretical approach to describe PADs from nonperturbative Resonance Enhanced Multi-Photon Ionization (REMPI) with ultrashort polarization-shaped laser pulses is presented and compared to experimental results. Applications of this technique to the generation and observation of atomic ring currents are discussed.     

Coherent population transfer in an atom by multiphoton adiabatic rapid passage

Coherent population transfer in an atom using a sequence of adiabatic rapid passages through single-photon resonances is well-known, but it requires that the frequency sweep match the changing frequencies of the atomic transitions. The same population transfer can be effected via a single multiphoton adiabatic rapid passage, which requires only a small frequency sweep, if it is possible to select the desired multiphoton transition from the many possible transitions. Here we report the observation of population transfer between Rydberg states by high order multiphoton adiabatic rapid passage.     

Generation of XUV attosecond pulses in the process of atomic ionization by few-cycle laser radiation

Ionization of a model two-electron atom in the presence of a strong field of ultrashort laser pulses is investigated using the numerical integration of the nonstationary Schrödinger equation, which describes the dynamics of a quantum system in the presence of an electromagnetic wave. The features of two-electron ionization in the presence of one-and two-cycle pulses are analyzed. The suppression of double ionization in the presence of ultrashort laser pulses related to a finite-time interelectron energy exchange upon the laser action is demonstrated. The features of the generation of high-order harmonics and single XUV attosecond pulses are studied for the atomic ionization by few-cycle laser pulses. The parameters of the laser pulse are optimized for the effective generation of a single XUV attosecond pulse.     

An experimental approach for investigating many-body phenomena in Rydberg-interacting quantum systems

Recent developments in the study of ultracold Rydberg gases demand an adwanced level of experimental sophistication, in which high atomic and optical densities must be combined with excellent control of external fields and sensitive Rydberg atom detection. We describe a tailored experimental system used to produce and study Rydberg-interacting atoms excited from dense ultracold atomic gases. The experiment has been optimized for fast duty cycles using a high flux cold atom source and a three beam optical dipole trap. The latter enables tuning of the atomic density and temperature over several orders of magnitude, all the way to the Bose--Einstein condensation transition. An elec- trode structure surrounding the atoms allows for precise control over electric fields and single-particle sensitive field ionization detection of Rydberg atoms. We review two experiments which highlight the influence of strong Rydberg---Rydberg interactions on different many-body systems. First, the Rydberg blockade effect is used to pre-structure an atomic gas prior to its spontaneous evolution into an ultracold plasma. Second, hybrid states of photons and atoms called dark-state polaritons are studied. By looking at the statistical distribution of Rydberg excited atoms we reveal correlations between dark-state polaritons. These experiments will ultimately provide a deeper understanding of many-body phenomena in strongly-interacting regimes, including the study of strongly-coupled plasmas and interfaces between atoms and light at the quantum level.