The advent of subfemtosecond or attosecond light pulses will open new fields of \nextreme nonlinear optics. Recently, experimental results on the production and \nmeasurement of a single 250-asec pulse were reported by Krausz et al [1]. This opens \nup new possibilities for studying and controlling electron dynamics in atoms and \nmolecules in asee time scale. Recently, Drescher et.al [2] has demonstrated that a \nlaser-based sampling system, consisting of a few-femtosecond visible light pulse and a \nasynchronized sub-femtosecond soft X-ray pulse, allows us to trace the relaxation \ndynamics directly in the time domain with attosecond resolution. Moreover, \nphotoionization and high-order harmonic generation (HHG) in molecular systems under \nthe action of combined infrared femtosecond and ultraviolet attosecond laser pulses \nwere investigated by Bandrauk and Shon [3]. It was shown that punctual "turn-on" of an \nasee pulse can trigger the ionization process, which in turn leads to significant \nenhancement of HHG. Despite the extensive work in this area, propagation of \nsubfemtosecond laser pulse has rarely been investigated.
The advent of subfemtosecond or attosecond light pulses will open new fields of \nextreme nonlinear optics. Recently, experimental results on the production and \nmeasurement of a single 250-asec pulse were reported by Krausz et al [1]. This opens \nup new possibilities for studying and controlling electron dynamics in atoms and \nmolecules in asee time scale. Recently, Drescher et.al [2] has demonstrated that a \nlaser-based sampling system, consisting of a few-femtosecond visible light pulse and a \nasynchronized sub-femtosecond soft X-ray pulse, allows us to trace the relaxation \ndynamics directly in the time domain with attosecond resolution. Moreover, \nphotoionization and high-order harmonic generation (HHG) in molecular systems under \nthe action of combined infrared femtosecond and ultraviolet attosecond laser pulses \nwere investigated by Bandrauk and Shon [3]. It was shown that punctual "turn-on" of an \nasee pulse can trigger the ionization process, which in turn leads to significant \nenhancement of HHG. Despite the extensive work in this area, propagation of \nsubfemtosecond laser pulse has rarely been investigated.
The past thirty years witnessed rapid developing of strong field physics that leads to the first generation of attosecond (10−18 s) pulses. The duration of available pulses has recently been reduced to less than 100 as, approaching the Kepler period of a classical electron revolving around the nucleus. For the first time, electron motions inside atoms, molecules and solids can be traced, probed and even steered in real time. It pushed the study on ultrafast dynamic processes into a new frontier, giving birth to attosecond physics. The development of attosecond pulses provides unprecedented coherent ultrashort XUV (extreme ultra-violet) of soft X-ray sources that enable imaging the atomic structure and resolving the related quantum dynamics for matter science. In particular, it allows the probing and monitoring of electron dynamics in the natural time scale of attoseconds with atomic spatial resolution. The generation and applications of attosecond pulses are directly related to the control and manipulation of the sub-cycle electron dynamics. Recent studies on the correlated multielectron dynamics have provided insight into the optical and dynamical properties of matter in the perspectives of time, phase and entanglement. It deepens our understanding on some of the fundamental questions, e.g., how the single or multiple photons are absorbed and how short are the quantum processes such as photoionization, tunneling ionization and charge migration. Although currently attosecond pulses are limited by the flux and pulse duration, the combination of attosecond pulses with intense infrared laser pulses paves new ways of controlling and probing electron dynamics in the domains of energy, time and space that lays the foundation for petahertz optoelectronics and attosecond pulse based transient spectroscopy. In this review, we will first briefly summarize the advancement of strong field and ultrafast physics including the relevant experimental findings, the theoretical explorations, the related technologies and the possible applications. Then we focus on the sub-cycle electron or multielectron dynamics and their manifestation on the ionization and coherent radiation properties. We start with the time behavior of Fano resonance and how it can be probed in time domain. In section 2, the correlated electron dynamics is discussed in term of anti-screening effect and Pauli effect that influence strong field ionization and high harmonic generation processes. In section 3, the coherent emission with frequency from terahertz to soft XUV and their joint measurement are discussed by emphasizing the generation mechanism of terahertz wave in two-color laser pulses. The developed high-harmonic and terahertz wave spectroscopy (HATS) is shown capable of imaging the molecular structure and dynamics. In section 4, the time-resolving of electron and hole dynamics and their coherence is proposed based on attosecond transient absorption technique. The coherence of ionization and the correlated electron dynamics is hinted crucial for electron-hole interaction. The topics are very limited and mainly selected from the perspectives of our group.
Recently, the advances in generation and characterization techniques of ultrashort laser pulses made it practical to prepare precisely defined laser pulses, these open up new possibilities for studying and controlling dynamical processes in femtosecond time scale. Hitherto, frequency-synthesized or chirped laser pulses have been widely applied to high-order harmonic generation (HHG) [3], population transfer [4], multiphoton transitions between Rydberg states [5], ect. Both the interference of two-color pulses and the nontrivial time dependence of chirped pulse laser field may lead to very interesting results. Moreover, recent studies have manifested that chirping can also have much impacts on the laser pulses as it propagates through different medium. For example, the propagation properties of chirped soliton pulses in optical nonlinear Kenmedia were investigated by Desaix et al. [6]. The result indicates that the properties of asymptotically emerging solitons depend not only on the magnitude, but also on the form of the initial chirp. In particular, the splitting of an initial pulse into separating soliton pulse pairs only occurs for certain classes of initial chirp functions. The influence of pulse shape and frequency chirp on stability of optical solitons was studied by Klaus and Shaw [7]. They found that destabilization occurs when eigenvalues of an associated Zakharov-Shabat system, which move along the positive imaginary axis with increasing chirp parameter, either are absorbed into the lower half plane or collide with a nother eigenvalue. Furthermore, the signal and group velocities for chirped pulses propagating through a GaAs cavity were measured by Centini et al. [8]. They showed that the chirp substantially modifies the group velocity of the pulse, but leaves the signal velocity unaltered.
Metastable states are important actors in the ionisation of atoms and molecules. Sub-femtosecond extreme ultraviolet pulses can coherently populate several transiently bound states at once, thus starting the attosecond clocks which are required to monitor and control ultrafast electronic evolution above the ionisation threshold. Here we illustrate, from a theoretical point of view, the effects coherent superpositions of 1 P o doubly excited states in the helium atom have on channel-resolved photoelectron spectra as well as on the transient absorption spectrum of the atom in the extreme ultraviolet region, when they are created by a single-attosecond pulse in the presence of a strong few-cycle near-infrared/visible pulse which acts as a probe. Interference fringes varying rapidly with the pump-probe time delay are visible in both photoelectron and transient absorption spectra. From such fringes, the wave packet itself can conceivably be reconstructed. Conversely, all observables are modulated by the characteristic beating periods of the wave packet, so that control of partial ionisation yields, branching ratios, and light absorption or amplification can be achieved.
When small quantum systems, atoms or molecules, absorb a high-energy photon, electrons are emitted with a well-defined energy and a highly symmetric angular distribution, ruled by energy quantization and parity conservation. These rules are based on approximations and symmetries which may break down when atoms are exposed to ultrashort and intense optical pulses. This raises the question of their universality for the simplest case of the photoelectric effect. Here we investigate photoionization of helium by a sequence of attosecond pulses in the presence of a weak infrared laser field. We continuously control the energy of the photoelectrons and introduce an asymmetry in their emission direction, at variance with the idealized rules mentioned above. This control, made possible by the extreme temporal confinement of the light-matter interaction, opens a road in attosecond science, namely, the manipulation of ultrafast processes with a tailored sequence of attosecond pulses.
Recently the measurement of X-ray pulses approaching the attosecond frontier was published (M. Drescher et al ., Science 291 (2001) p. 1923). The attosecond laser pulse enables the study and control of the motion of electrons inside atoms. In this paper we develop and solve the modified Schrödinger equation (MSE) which describes the interaction of electrons with its surroundings in an atom. This interaction can be detected only using an attosecond laser pulse within the relaxation time of the interaction which is of the order of 10 attoseconds.
FOREWORD by N. Bloembergen NONLINEAR OPTICS Channeling of atoms in a standing laser light wave by V.I. Balykin et al. Optical nonlinearities and the Kerr effect in phaseonium by U. Rathe et al. Spectroscopic studies in the far ultraviolet (80-200nm) using nonlinear tunable sources by B.P. Stoicheff CARS in plasma physics by M. Lefebvre et al. Velocity distribution of electrons for tunnel ionization by a light field with polar asymmetry by N.B. Baranova and B. Ya Zel'dovich NONLINEAR OPTICS IN CONDENSED MEDIA Hot carriers in semiconductors studied via picosecond optical nonlinearities in the infrared by T. Elsasser and W. Kaiser Non-local time-resolved spectroscopy-tracking of polariton pulses in crystals by Ch Flytzanis et al. Self trapping of optical beams in photorefractive media by M. Segev et al. Solitons in quantum nonlinear optics by R.Y. Chiao et al. Femtosecond dynamics of third-order nonlinearities in polythiophenes by A Cybo-Ottone et al. NEW DEVICES AND TECHNOLOGY Nonlinear generation of sub-psec pulses of THz electromagnetic radiation by optoelectronics-applications to time-domain spectroscopy by D. Grischkowsky Novel nonlinear optical techniques for studying chiral molecules of biological importance by N.I. Koroteev Coupled nonlinear cavities: new avenues to ultrashort pulses by F. Mitschke et al. Transverse rotating waves in nonlinear optical systems with spatial and temporal delay by N.G. Iroshnikov and M.A. Vorontsov The effect of intraspectral harmonics correlation of broad-band fields on the excitation of quantum resonance systems by A.M. Bonch-Bruevich and S.B. Przhibelskii Injection-locked femtosecond parametric oscillators in LBO crystals by V.M. Gordienko et al. INDEX