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We study the single and double ionization yields and the dissociation dynamics of a one-dimensional two-electron molecule exposed to a laser pulse of intensity IL in the range 1013 − 1015 W/cm2 and photon energy hω¯L =3.18 eV. The calculations are carried out in the case of both fixed and movable nuclei. At low IL the ionization curves have a power law shape In that is interrupted by a knee at higher intensity.

The dynamics of hydrogen-like molecules is investigated beyond the usual fixed nuclei approximation. The nuclear motion introduces in the familiar spectrum of emitted radiation additional regular lines whose separation is essentially given by the vibrational frequency of nuclear motion. A wavelet analysis of the emitted spectrum shows that the intensity of the harmonic lines is modulated with the same period of the nuclear motion; this suggests the possibility of the real-time control of the nuclear dynamics.

Accurate numerical calculations are carried out to investigate the validity of the two-state approximation in the case of resonant interactions between electromagnetic radiation and atoms . Short pulses are considered and the presence of the atomic spectrum is modelled by introducing a third, nonresonant, state . We show that the harmonics of the pulse profile may play a significant role in the dynamics of the process and may cause energy nonconserving transitions between the atomic states. © 1990 Taylor & Francis Ltd.

We study the single and double ionization yields and the dissociation dynamics of a onedimensional two-electron molecule exposed to an intense laser pulse. The double ionization yields are systematically investigated for both fixed and moveable nuclei. At low intensities the ionization curves have a power law shape, followed by a knee profile for higher intensities. A temporal correlation between the nuclear motion and the electron ionization shows that the nuclear motion deeply affects the ionization yield.

In this paper we show how it is possible to investigate the nuclei dynamics of a D2+ molecular ion by using the high harmonic generation spectra emitted by the system when subjected to an intense laser field. In particular, the emitted spectra contains, in addition to the usual odd harmonic peaks, additional satellite peaks whose frequency spacing is equal to the vibrational frequency of the nuclei.

The electromagnetic spectrum emitted by a molecule driven by a laser presents harmonics and satellite lines whose separation is equal to the oscillation frequency of the nuclei. Full quantum and semiclassical calculations are presented.

We study the behaviour of a homonuclear molecule driven by an intense laser field. Newton's laws are used to describe the dynamics of nuclei while the quantal approach is reserved to the study of the electron. It is observed that the nuclei can oscillate or dissociate according to the degree of ionization of the molecule. In case of low ionization rate it is shown that great amount of information can be obtained by using the simplified approaches of fixed nuclei and of two-state approximation. Under suitable conditions the electron wave function spends a long time localized around one nucleus. The harmonic generation of the molecule is studied and seen to contain even harmonics.

The dynamics of a diatomic one-dimensional homonuclear molecule driven by a two-laser field is investigated beyond the usual fixed nuclei approximation. The dynamics of the nuclei is treated by means of Newton equations of motion; the full quantum description is used for the single active electron. The first laser pulse (pump) excites vibrations of the nuclei, while the second very short pulse (probe) has the role of confining the electron around one of the nuclei. We show how to use the radiation scattered in these conditions by the molecule to achieve real-time control of the molecular dynamics.

In this work we study harmonic emission from structured quantum rings (SQRs). In SQRs, electrons trapped in two-dimensional structures are further confined by an external potential composed of N scattering centers arranged on a circle. We build a suitable one-dimensional model Hamiltonian describing this class of systems and analytically solve the associated Schödinger equation. We find that the solution can be expressed in terms of Mathieu functions and focus on the specific case of N = 6. By exactly solving the time-dependent Schödinger equation, we then show how the harmonic response to linearly polarized lasers strongly depends on the ring physical parameters. The results illustrate how the additional degrees of freedom introduced by these parameters provide important handles to control the emitted spectrum that in some cases extends into the XUV region.

We study the ionization dynamics of a model one-dimensional molecular ion as a function of the internuclear distance R, for different values of the laser intensity. The electron–nucleus potential is assumed to be a Poschl–Teller potential, whose parameters are chosen to have only two bare bound molecular states in the range of R considered. We describe three different theoretical approaches to study the dynamics of the system: an exact numerical, a semiperturbative and a phenomenological approach. All these approaches indicate the presence of a sharp ionization peak for a critical value of the internuclear distance, for which the energy difference between the two bound levels coincides with the laser photon energy. The results obtained are explained and a new model of molecular ionization in intense laser field is presented.

We study a simple model atom that has two bound states and a continuum of free states, interacting with a strong electromagnetic field. In our analysis we assume that only the continuum-continuum transitions occur- ring between degenerate free states are important for the dynamics of the atomic system; adopting this sim- plifying hypothesis, we show that it is possible to describe the time evolution of the atom by means of an infinite but discrete set of first-order differential equations describing a formal model atom that has two bound states and a degenerate quasicontinuum of states. Moreover, these equations depend on a small number of parameters of the bare atom and of the external laser pulse. The role of these parameters in the laser-atom dynamics is investigated.

The dynamics of a H2+ molecular ion driven by two laser pulses separated by a time lag is studied beyond the Born-Oppenheimer approximation. The first, short, pulse prepares the molecule in some quantum state, which is probed by the second pulse. Under suitable conditions, the molecule emits a spectrum of redshifted high-order harmonics. The value of the redshift is proportional to the harmonic order and can be used as a measure of the speed of the atoms of the molecule.

We describe, using a semiclassical approach, the molecular dynamics of a one-dimensional H2 molecule interacting with a laser, beyond the Born–Oppenheimer approximation. We observe and discuss different molecular behaviors, such as ionization and dissociation.

The dynamics of an electron wave packet in the presence of laser radiation and of a one-dimensional repulsive soft-core potential is investigated. For different laser intensities and for different initial positions of the electron wave packet, these results are compared with those for an attractive potential. The repulsive potential is capable of confining the electron quite efficiently under appropriate conditions. In these conditions, the electron is shown to emit a high harmonic spectrum similar to that emitted by the more conventional attractive potential. It is thus argued that recombination into an atomic bound state as required by the three step model is not essential for the emission of high harmonics.

The spectrum emitted by a three-level atom in the presence of a weak laser field is given together with the population dynamics and the phase of the Fourier transform of the acceleration. Calculations show that the spectrum can be very different from that emitted by a two-level atom. When the trapping conditions are obtained, the coupling to the third level can result in a large change in the spectrum.

We present the results of experimental and theoretical studies of high-order harmonic generation (HHG) in plasmas containing fullerenes using pulses of different duration and wavelength. We find that the harmonic cutoff is extended in the case of few-cycle pulses (3.5 fs, 29th harmonic) compared to longer laser pulses (40 fs, 25th harmonic) at the same intensity. Our studies also include HHG in fullerenes using 1300 and 780 nm multicycle (35 and 40 fs) pulses. For 1300 nm pulses, an extension of the harmonic cutoff to the 41st order was obtained, with a decrease in conversion efficiency that is consistent with theoretical predictions based on wave packet spreading for single atoms. Theoretical calculations of fullerene harmonic spectra using the single active electron approximation were carried out for both few-cycle and multicycle pulses.

The collision of an electron against a repulsive potential in the presence of a laser field is investigated. It is found that a sufficiently strong laser field forces the electron to remain in the neighbourhood of the repulsive potential causing bremsstrahlung. By appropriately filtering the emitted signal, an electron in the presence of a repulsive potential is capable of generating attosecond pulses.

An iterative method to obtain a solution of the differential equation $$i\dot a = \hat H(t)a$$ , with Ĥ a 3×3 Hermitian matrix anda the unknown vector, is proposed. The procedure is particularly suitable for computer implementation and, as an example, has been applied to find the excitation probability of a three-level atom after the synchronous passage of two laser pulses each almost resonant with a pair of atomic levels.

In this work we study the radiation diffused by a fictitious structured nanoring driven by an intense laser field. In our model we consider an electron moving through a cosine-shape potential. The results show that the ring, under particular conditions, emits a wide spectrum of harmonics.