摘要:

We discuss recent developments in the generation of ultra-intense laser pulses and show how these can be used to study matter in the presence of electric fields that compete with that due to the nucleus. This has led to a very rapid growth in a wide range of multiphoton studies, many of which are represented in this volume.

ISSN:0950-0340    

DOI:10.1080/09500348914550921

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

We have calculated the spatial and electron energy structure for short-pulse high-intensity multiphoton ionization taking into account saturation. Using an avoided-crossing picture, we have modelled multiphoton resonances induced by the high-intensity a.c. Stark effect. We have explicitly considered ionization due to the rising and falling edges of the laser pulse including saturation and ground-state depletion. Using only the laser-pulse duration as the adjustable parameter, our results show the dramatic modifications both to the spatial structure and to the photoelectron energy spectrum as saturation becomes important.

ISSN:0950-0340    

DOI:10.1080/09500348914550931

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

We present theoretical work on high-order harmonic generation accompanying multiphoton ionization of atoms in intense laser fields. We first review some elements of the theory of harmonic generation, particularly the limitations imposed by perturbation theory and some aspects of phase-matching at high pump intensities. A new non-perturbative approach to the theory based on the direct numerical solution of the time-dependent Schrödinger wave equation is described.

ISSN:0950-0340    

DOI:10.1080/09500348914550941

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

We discuss effects of optical depth, beam focusing and non-perturbative atomic response on the spectrum of optical harmonics generated by an intense beam of laser radiation (up to 1014W cm−2) in a small volume of atomic vapour. We find remarkable enhancement of high harmonics at intensities beyond the perturbative limit.

ISSN:0950-0340    

DOI:10.1080/09500348914550951

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

We derive a field-dressed Coulomb continuum state and discuss its application in the calculation of intense-field multiphoton ionizations.

ISSN:0950-0340    

DOI:10.1080/09500348914550961

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The multiphoton ionization of helium by a strong radiation field having a wavelength of 1064 nm and a field intensity up to 5 × 1014W cm−2is considered within a non-perturbative treatment partially accounting for the electron-electron correlations in the initial bound state and approximately for the Coulomb interaction between the residual ion and the ejected electron in the final state. Only single-electron transitions are considered, the main emphasis being on the field polarization effects. The obtained results are compared with the few results available in the literature in the same regime as well as with very recent experimental findings. In particular, the calculated photoelectron energy spectra, angular distributions and ionization rates are found to reproduce satisfactorily all the main features observed in the experiments. The proposed formalism appears to be a particularly flexible method for studying field polarization effects; for the channel-by-channel analysis in the case of strong fields; and for multiphoton processes of very large order. Potential development and improvement of the technique is discussed.

ISSN:0950-0340    

DOI:10.1080/09500348914550971

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

An approximate non-perturbative theory of multiphoton ionization of a hydrogen atom by two strong radiation fields is outlined. The special case is then considered for when one of the fields is of low intensity and high frequency and the other field is of high intensity and low frequency. A set of representative calculations has been performed for this case; that is, (a) angular distributions for given numbers of absorbed and emitted low-frequency photons and different geometries; (b) total cross-sectionsversusthe strong-field intensity; (c) angular distributions summed over all the low-frequency photon exchanges, showing a fourfold symmetry in a geometry in which each ionization channel exhibits, instead, only a twofold symmetry; (d) the average energy gained by the ejected electrons. Calculations are performed for a strong low-frequency field of arbitrary polarization. In many respects, the present calculations are expected to complement those of single-field multiphoton ionization. It is hoped that the results of the calculations reported here may prompt systematic measurements also in this new class of processes, as the predictions are well within the state of the art of present multiphoton-ionization experiments.

ISSN:0950-0340    

DOI:10.1080/09500348914550981

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

We present a simple model for two-electron excitation and ionization of an atom in the presence of an intense laser field. We show, in particular, how the Coulomb interaction, via configuration interaction, prevents the excitation and ionization from being collective in all but the most intense fields. By collective we mean that each electron has the same spatial wavefunction: this implies that the electron pair may be described by a restricted time-dependent Hartree-Fock wavefunction. The configuration interaction prevents collective behaviour not only through the process of auto-ionization but also through the mixing of doubly excited independent electron states into the ground state. We are able to give criteria for establishing true collective excitation and ionization of our model two-electron system in an intense field.

ISSN:0950-0340    

DOI:10.1080/09500348914550991

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The optical double-resonance spectrum for a three-level atom interacting with two monochromatic laser pulses with arbitrary temporal profiles is calculated by use of Light's perturbation theory. Unlike some earlier work, the theory is not restricted to exact resonance of the pump laser, or to pulse areas which are exact multiples of 2π. A variety of pulse profiles are investigated, and the spectra are found to depend strongly on the detuning of the pump laser.

ISSN:0950-0340    

DOI:10.1080/09500348914551001

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Within an analytically solvable model, the theory is studied of the effects of atomic-level structure both on ionisation and on the fluorescence spectrum of double optical resonance. Peaks due to this structure, which appear in addition to the Autler-Townes doublet, can now be given a concise description by means of an analytical formula that has a wide range of application. To illustrate the theory, the formula is applied to the cases of barium and sodium.

ISSN:0950-0340    

DOI:10.1080/09500348914551011

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor