摘要:

The recent development of lasers capable of delivering short pulses of very intense radiation, over a frequency range extending from the infrared to the ultraviolet, has led to the discovery of new phenomena in laser interactions with atomic systems. In the first part of this article, a survey is given of the basic properties found in the study of multiphoton processes such as the multiphoton ionization of atoms, the emission by atoms of high order harmonics of the exciting laser light and laser-assisted electron-atom collisions. The second part contains a review of the main non-perturbative methods, based on the Floquet approach or the numerical solution of the time-dependent equations for the wave function, which have been used to perform theoretical studies of these processes. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55247

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We present an analysis of nonlinear optical effects when a high intense ultrashort laser pulse comprising only few field cycles propagates through an ionized medium. We introduce a model for the optical pulse and plasma based on the real electric field representation and the quantum mechanical description of electron dynamics in the ionization process. In the first part, we study the nonlinear atom response to such short driving pulses and the accompanied process of attosecond continuum production. In the second part, we analyze some collective plasma phenomena with ultrashort driving pulses, for which transverse effects are important. Among them, the processes of leaking mode self-channeling at saturable ionization, induced ionization scattering and large blueshifting with pulse shortening to a single-optical-cycle burst are of particular interest. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55221

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The general dispersion relation for electron parametric instabilities of an ultra-intense circularly polarized laser wave is established for arbitrary plasma density. It corresponds to a generalization of the stimulated Raman scattering instability, the relativistic modulational instability, the relativistic filamentation instability, and the two plasmons decay instability. In the relativistic regime the generalized instability is characterized by a wide extent of the unstable region in the wave vector space, with growth rates reaching a fraction of the laser frequency, and a strong harmonic generation. One-dimensional and two-dimensional particle-in-cell simulations confirm these results. In particular a systematic study of the propagation of very intense laser pulses through slabs of plasma of several tens of microns are presented. The instability leads to a rapid longitudinal and transverse electron heating, and to filamentary structures which progressively merge in a nonlinear stage. The heating results in highly energetic electrons with energy of several tens of MeV. Correlatively, a strong attenuation rate of the electromagnetic wave is observed. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55241

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report on strong line emission from overdense plasma layers at the second (and also third) harmonic of the plasma frequency&ohgr;p,when irradiated by intense ultra-short laser pulses. The results are obtained from one-dimensional particle-in-cell simulations. The emission is interpreted as conversion of two (or more) plasmons into a photon. Electron jets, generated by laser interaction at the surface, produce the plasmons. Phase matching requires counterpropagating plasmons which arise either from two-sided laser irradiation or electrons returning from the rear side.

ISSN:0094-243X    

DOI:10.1063/1.55197

出版商:AIP    

年代:1998

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.55255

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We discuss a kinetic model for a system of free and bound electrons undergoing field ionization. Fluid equations are derived and used to study transient ionization effects on short laser pulse propagation. We finally discuss a suitable semiclassical fluid approach to heavy atoms ionization. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55259

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The interaction of 1.5 ps FWHM laser pulses with solid targets at intensity1015–1017 W/cm2and contrast ratio106is studied. Red shift of a “mirror” reflected fundamental wave and its second harmonic depending on the incident laser pulse energy and angle of incidence are observed. They are associated with Doppler shift corresponding to inward movement of the critical density surface from laser pondermotive pressure. Back scattered light has nonlinear dependence from laser intensity connected with SBS and changing of plasma surface. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55260

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In this contribution we analyse the possibility of generating a grating structure in a plasma surface through the interaction of two crossed laser beams. We present one-dimensional particle-in-cell calculations that show that surface electron-density fringes can be induced by the beams if they ares-polarised. Finally, we give approximated analytical expressions for the time-averaged electron density which enclose information about the fringe width and maximum and minimum electron densities (i.e. fringe “visibility”). ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55261

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The mathematical scheme that allows to calculate the dispersion characteristics of surface waves propagating along the boundary of a plasma with arbitrary fixed density profiles is proposed. Collisional and resonance damping are taken into consideration. Properties of surface wave propagation for different target materials have been investigated. Appropriate conditions of direct excitation of surface waves have been suggested. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55262

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

When an intense laser pulse propagates through a cluster gas it is shown that a plasma channel with a refractive index higher than its surrounding region is produced. In the high intensity regime, that leads to a novel self-confinement effect which keeps the laser beam from diverging. This effect is of importance for ultrashort pulse durations, less than 100–300 fs, depending on ion mass, and is limited by the expansion process caused by strong heating in the near-solid density cluster microplasma. A computational study of the self-confinement effect has been performed where long plasma channels were demonstrated. ©1998 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.55263

出版商:AIP    

年代:1998

数据来源: AIP