We present two interferometry schemes in the extreme ultraviolet, based on either the wave-front division of a unique harmonic beam (1st scheme) or two spatially separated, phase-locked harmonic sources (2nd scheme). In the first scheme using a Fresnel bimirror interferometer, we measure the degree of spatial coherence of the 13th harmonic generated in xenon, as a function of different parameters. A high degree of coherence, larger than 0.5, is found for the best conditions in almost the full section of the beam. Then, we demonstrate that the second scheme can be used for interferometry measurements with an ultrahigh time resolution. The 11th harmonic is used to study the spatial variation of the electron density of a laser-produced plasma. Electronic densities higher than 2.1020 cm−3 are measured.

Clusters represent a new class of laser pulse targets which show both the properties of underdense and of overdense plasmas. We present analytical and numerical results (based on 2D- and 3D-PIC simulations) of the Coulomb explosion of the ion cloud that is formed when a cluster is irradiated by a high-intensity laser pulse. For laser pulse intensities in the range of 1021−1022 W/cm2, the laser light can rip electrons from atoms almost instantaneously and can create a cloud made of an electrically nonneutral plasma. Ions can then be accelerated up to high energy during the Coulomb explosion of the cloud.

We have measured multi-keV protons and ∼100 keV iodine ions from the interaction of intense, femtosecond laser pulses with atomic Xe clusters and mixed-species HI clusters. The explosion dynamics of the HI clusters differs from the pure H and I cluster cases, with the iodine energies being substantially reduced. Mixed-species clusters provide a possible route for boosting the explosion energies of low-Z ions, and extend the advantages of the laser-cluster interaction to species that do not readily form pure clusters.

Rare gas or lead clusters of several hundreds to many thousands of atoms per cluster were irradiated by intense laser pulses producing peak intensities up to 1017W/cm2. Fast, highly charged fragment ions were observed by means of standard TOF mass spectrometry as well as a magnetic deflection TOF device (MDTOF). Charge states of up to Xe30+ or Pb18+ were detected with maximum kinetic energies reaching far beyond 100 keV for Xe. A strong dependence of the charging and heating process on the laser pulse duration was found. While the resulting ionic fragment spectra are qualitatively similar for rare gas and lead clusters, the kinetic energies for the metal clusters seem to be significantly lower.

Recently, there has been great interest growing in ultrahigh field particle acceleration driven by ultraintense laser interactions with beams and plasmas. Although numerous concepts of particle acceleration by laser fields have been proposed almost since the beginning of the laser evolution, there has been tremendous progress in recent years on their theoretical and experimental aspects owing to advances in the generation of ultraintense short laser pulses. The laser–plasma accelerator concepts are reviewed on the laser wakefield acceleration mechanism. In particular, the electron acceleration by the laser wakefield in plasmas is illustrated by our recent experimental results, including the propagation of the ultrashort intense laser pulses in plasmas.

During the diffraction of a femtosecond pulse with a grating, apart spectral filtering, there occurs a time stretching due to the difference in the path length among the rays diffracted, even of equal wavelength. The reason resides in the action of the grating: to depart from the behavior of the mirror, that is, α = β, and to direct the rays in directions whose paths are groove-by-groove different of mλ. The compensation of this broadening is studied in the following by using a pair of grating in a particular mounting. The configuration is studied for the application in the selection of one single laser harmonics in the framework of high order harmonic generation processes.

A kinetic theory for quantum many-particle systems in time-dependent electromagnetic fields is developed based on a gauge-invariant formulation. The resulting kinetic equation generalizes previous results to quantum systems and includes many-body effects. It is, in particular, applicable to the interaction of strong laser fields with dense correlated plasmas. Numerical results are obtained for the cycle-averaged electron–ion collision frequency in a high-frequency field.

The role of collisional absorption is supposed to be important in the beginning of the interaction between a laser pulse and matter. Later on, collective absorption phenomenons take place. The scope of this paper is to present first results about the so-called AC-run-away effect, defined as a “sudden transition from collisional absorption regime to a collective one.” For this purpose, we use a simple model based on ballistic theory. The delicate point concerning the Coulomb logarithm is also studied: we propose for it a convenient cutoff and an ensemble averaged Coulomb logarithm fit formula. Another application of the model presented here is the normal skin effect. We show some sensible differences between the present approach and those based on more common and rough collision frequency formulas.

The effect of the relative phase between the components of a bichromatic field of frequencies ω and 3ω is discussed in the case of free–free transitions in laser-assisted electron-hydrogen scattering. For fast projectile and low field intensities, the role of target dressing is pointed out.

We report time-dependent simulations of the evolution of atoms, molecules, and solids in the presence of intense electromagnetic radiation using the density functional theory. In the case of the ionic degrees of freedom we find that selective breaking of strong bonds may be possible at off-resonant infrared frequencies by a novel “concerted kick” mechanism. In the case of the electron response we find the following: free atoms and ions under intense infrared light respond with high harmonics in the X-ray regime; for a free molecule (Si2), we predict an unusual third harmonic response to a UV pulse centered at a frequency equal to the primary electronic excitation of the molecule; for a semiconductor (Si), we find several odd harmonics in response to a continuous wave of subgap infrared radiation. Prospects for future calculations are discussed.

Intense continua of electromagnetic radiation of very brief duration are formed in the interaction of focused ultra-short terawatt laser pulses with matter. Two different kinds of experiments, which have been performed utilizing the Lund 10 Hz titanium-doped sapphire terawatt laser system are being described, where visible radiation and X-rays, respectively, have been generated. Focusing into water leads to the generation of a light continuum through self-phase modulation. The propagation of the light through tissue was studied addressing questions related to optical mammography and specific chromophore absorption. When terawatt laser pulses are focused onto a solid target with high nuclear charge Z, intense X-ray radiation of few ps duration and with energies exceeding hundreds of keV is emitted. Biomedical applications of this radiation are described, including differential absorption and gated-viewing imaging.

Equations (10)–(12) and (14)–(16) of this paper, as well as the paragraph following (16), contain errors and should be corrected as follows (primes indicate corrected equations). The corrections do not alter the analyses and conclusions in the remainder of the paper.

Article appeared in Laser and Particle Beams (1998), 16, 295–316