Sökresultat

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.

Bone Mineral Density (BMD) is a highly heritable trait, but genome-wide association studies have identified few genetic risk factors. Epidemiological studies suggest associations between BMD and several traits and diseases, but the nature of the suggestive comorbidity is still unknown. We used a novel genetic pleiotropy-informed conditional False Discovery Rate (FDR) method to identify single nucl

High mechanical load in alternating directions with sufficient rest in between the loading periods is one of the best stimuli to enhance bone mass and skeletal structure, both contributing independently to bone strength. The age-frame where skeletal benefits from exercise are largest is in late pre- and early peri-puberty. Recent publications with low level of evidence infer that such skeletal ben

Medial tibial stress syndrome, a common condition of uncertain origin found in athletes, is characterized by pain in the distal posteromedial aspect of the tibia during exercise, with or without increased scintigraphic uptake in the affected region. To determine whether medial tibial stress syndrome with increased scintigraphic uptake is associated with a change in tibial bone mineral density conf

Exercise is associated with increased peak bone mineral density (BMD). To determine the relationship between the duration of exercise and BMD, we measured BMD of the axial and appendicular skeleton by dual-energy X-ray absorptiometry (DXA), and speed of sound (SOS), broadband attenuation (BUA), and stiffness index by quantitative ultrasound (QUS) of the calcaneus, in 67 active male national soccer

This prospective study evaluated bone loss in the peri- and postmenopausal period in 156 women followed from age 48 to 64 years. All women were premenopausal at the start of the study. Areal bone mineral density (g/cm2) was measured by single-photon absorptiometry (SPA) of the forearm at the 1 cm level (BMD 1 cm) and the 6 cm level (BMD 6 cm) every second year. Onset of menopause (MP) was determin