Search results

We present experiments, supported by time-dependent Schrödinger simulations, on the dynamics of Helium bound states after an attosecond excitation in the presence of a strong infrared laser field.

The essence of ELI-ALPS, the laser driven secondary sources ranging from X-ray and X-UV to THz with duration as short as tens of attoseconds, are designed to be available for users from 2016.

We discuss the role of many-electron interactions in multiphoton multielectron ionization of heavy atoms and try to indicate the relative importance of collective effects and screening, relaxation and shakeup, and Fermi sea correlations. The purpose of the work is to look for approximations in which the photoemission processes have been renormalized in consistent ways with respect to the field and

We report the angular distributions of high-order harmonic radiation generated in neon and in argon using a 140 fs Cr:LisAF laser system. The profiles show an evolution from Gaussian to near flat-top. No substructure is observed except at the highest intensity in a completely ionized gas. The divergence of the harmonics is found to depend essentially on whether they belong to the plateau or to the

We study the role of propagation effects in high-order harmonic-generation experiments. The phase-matching integrals are calculated in the weak-field limit by taking into account the dispersion of the rare-gas medium at each harmonic frequency and the absorption of the harmonics. The refractive indices of the rare gases are deduced from a calculation of the dynamic polarizabilities within the fram

We present theoretical studies of high-order harmonic generation in a rare-gas medium. The experimental results obtained at Saclay with a 1064 nm Nd-YAG laser in the 1013 W cm-2 intensity range are summarized. The harmonic emission strengths first decrease rather steeply for the first orders, then form a long plateau up to the 21st harmonic in xenon, or up to the 33rd harmonic in argon, before dec

The energy spectra of electrons produced in multiphoton ionization of rare gases display a large number of peaks corresponding to the absorption of much more than a minimum number of photons required to ionize the atom. A retarding-potential method has been used to analyze the energy of electrons produced in the multiphoton ionization of He, Ne, and Xe at 1064 and 532 nm in a broad range of laser

We present high-order harmonic generation results obtained with different laser systems a 1 ps 1053 nm Nd-glass laser a 2 ps 616 nm synchronously pumped dye laser a 36 ps 1064 nm mode-locked Nd-YAG laser and the second harmonics (308 nm and 532 nm) of the latter two systems. We investigate the influence of the laser pulse width the excitation wavelength (from the near infrared to the ultraviolet)

We present a theoretical analysis of a recent experiment [J. Opt. Soc. Am. B 6, 1513 (1989)] on two-color threephotonionization of Xe through resonant even-parity Rydberg states. We calculate second-order ac-Stark shifts, two-photon Rabi frequencies, and ionization widths by using wave functions obtained from a multichannel quantum-defect-theory analysis of the Rydberg series in Xe. We perform a d

The radiative lifetime of the ls2p1P state of helium is measured in a two-colour ionization experiment with a 5% accuracy. The state is excited by the 13th harmonic of a tunable SO ps laser and ionized by a synchronous ultraviolet laser, with a variable time delay. This experiment demonstrates that the high harmonics generated in a jet of rare gas exposed to an intense laser field provide a tunabl

We present experimental results on high-order harmonic generation in xenon, using a Nd:YAG laser (1064 nm). The harmonic generation efficiency is studied as a function of the laser intensity in the 1013 W/cm2 range. The harmonic conversion rates show a significant change of behavior when the medium becomes ionized (∼1013 W/cm2). This effect can be understood as the change of the nonlinear response

We investigate the origin of the period distribution of giant planets. We fit the bias-corrected distribution of gas-giant planets inside 300 d found by Santerne et al. using a planet formation model based on pebble accretion. We investigate two possible initial conditions: a linear distribution of planetary seeds, and seeds injected exclusively on the water and CO icelines. Our simulations exclud

We present a simple experimental setup that makes possible the measurement of the beam section at focus under full-power conditions. We demonstrate that a 1.5-TW laser system can be focused down to a 13.5-μm-diameter spot using conventional lens focalization, thus achieving laser intensities of up to 1018 W/cm2.

We report experimental studies of harmonic generation in Xe using a 1064 nm Nd-YAG laser. Third-harmonic conversion is observed in a positively dispersive medium, using a tight-focusing geometry. The intensity of third-harmonic generation in a gas cell varies much more steeply with the laser intensity than a cubic law. The reason for the breaking of the phase matching condition is discussed.

The processes that led to the formation of the planetary bodies in the Solar system are still not fully understood. Using the results obtained with the comprehensive suite of instruments onboard the European Space Agency's Rosetta mission, we present evidence that comet 67P/Churyumov-Gerasimenko likely formed through the gentle gravitational collapse of a bound clump of mm-sized dust aggregates ('

Nonresonant ac Stark shifts of Rydberg states in Xe have been investigated by probing an atomic transition with a weak UV light in the presence of an intense YAG-laser pulse. Rydberg atoms produced through two-photon excitation, 5p → np (n = 15-48) and 5p → nf (n = 12-49), are subsequently ionized. IR-laser-induced shifts of the resonant ionization profiles are then measured. The measured shift, 3

The energies of the np[1/2]o, np[3/2]2, np[5/212, nf[3/2] 2, and nf[5/2]2 Rydberg states in Xe are measured within +0.3/-0.5 cm-1 from n = 12 to n = 49. The Rydberg states are excited by nonresonant two-photon absorption and detected by dc field ionization or infrared photoionization. We determine the ionization limit and the quantum defects for the different series involved.