[en] We have performed the double-pulse coherent control of nuclear wave packets, where the sequence of two identical femtosecond laser pulses generates two identical nuclear wave packets in the A³0⁺ state of the single Hg-Ar van der Waals complex. The time delay between the two laser pulses is tuned with an accuracy in attosecond time scale to induce constructive and destructive interferences of the two nuclear wave packets. The interferogram measured by scanning the time delay shows a high-frequency oscillation with a period of 830 attoseconds. Wave packets have been manipulated in attosecond time scale for the first time

[en] Absolute reduced absorption coefficients for the Hg resonance line at 253.7 nm broadened by Ar were determined between 390 and 430 K in the spectral range from 20 to 1000 cm^-1 on the red wing and from 20 to 400 cm^-1 on the blue wing. The resultant reduced absorption coefficients are in fair agreement with those obtained by Petzold and Behmenburg [Z. Naturtorsch. Teil A 33, 1461 (1978)]. The observed A³0⁺left-arrow X¹0⁺ spectrum in the spectral range from 80 to 800 cm^-1 on the red wing agrees remarkably well both in shape and magnitude with the quasistatic line shape calculated using the potential-energy curves of the HgAr van der Waals molecule given by Fuke, Saito, and Kaya [J. Chem. Phys. 81, 2591 (1984)], and Yamanouchi et al. [J. Chem. Phys. 88, 205 (1988)]. The blue-wing spectrum is interpreted as the B³1 left-arrow X¹0⁺ free-free transition of HgAr by a simulation of the spectrum using uniform semiclassical treatment for the free-free Franck-Condon factor. The source of the satellites on the blue wing is attributed to the phase-interference effect arising from a stationary phase-shift difference between the B- and X-state translational wave functions. The stationary phase-shift difference arises owing to the existence of a maximum in the difference potential between the B and X states. The repulsive branches of the potential-energy curves of HgAr for the X and B states have been revised to give excellent agreement between the observed and calculated spectra, both in shape and magnitude. copyright 1996 The American Physical Society

[en] Hydrides re-orientation characteristics and its effects on the mechanical properties of spent fuel claddings have been studied experimentally using un-irradiated Zircaloy-4 cladding tubes. Effective radial re-orientation factor (Fe) which means the ratio of precipitated hydrides in radial direction to dissolved hydrides at test temperature was estimated from the measured radial orientation factor (Fn) and hydrogen content in the test sample. Fe was correlated with the test temperature and the loaded hoop stress. It is shown that the higher the temperature, the greater the Fe at the same hoop stress. The threshold stress of re-orientation to radial direction is around 100MPa at 300degC. To examine the effect of radial re-orientation of hydrides on cladding mechanical properties, ring tensile tests and axial tensile tests have been performed on re-oriented samples at room temperature. The results show that radial hydrides have no clear effect on the axial and circumferential yield stress of Zircaloy-4 cladding tubes in the range of our test condition. From these results it is concluded that although some hydrides may precipitate in radial direction of cladding tubes during dry storage of PWR spent fuel, such hydride precipitates have no clear influence on the mechanical strength of cladding tubes. (author)

[en] Anisotropic photofragmentation of SF₆ following F 1s excitation is ascribed to the localization of the valence holes created as a result of the Auger decay of the F 1s core hole, itself polarized by excitation with linearly polarized light. Theoretical calculations based on the localized core-hole model are in reasonable agreement with the observation. copyright 1997 The American Physical Society

[en] High-resolution electron-ion coincidence spectroscopy is used to (i) map correlations between electrons and ions from atomlike ionization of ethanol by intense 400 and 800 nm light pulses and (ii) disentangle the effects of dissociative multiphoton (MPI) and tunneling (TI) ionization. Electron spectra correlated with Cⁿ⁺ (n=1,2,3) exhibit a continuum structure with a high-energy tail due to inelastic collisions involving rescattered electrons following TI, while those correlated with C₂H_nO⁺ have structure characteristic of MPI and above-threshold ionization

[en] We report experimental and theoretical laser-induced photoelectron spectra of Ne, Ar, Kr and Xe in the direction of the laser polarization at laser intensities in the region 0.5-3.2 x 10¹⁴Wcm^-2. For Ar and Xe, spectra at different angles are also presented for the laser intensities of 2.4 x 10¹⁴Wcm^-2 for Ar and 1.3 x 10¹⁴Wcm^-2 for Xe. Resonance-like structures evolve as a function of the laser intensity in the longitudinal spectra, which become suppressed at large angles. The simulations are in the context of the strong-field approximation, which is augmented to account for rescattering and the atom-specific electron-positive-ion scattering potentials, and they include focal averaging as well as saturation. Agreement between the data and these simulations is generally fair, especially for intensities below the saturation regime.

[en] Angle-resolved high-order above-threshold-ionization spectra are presented which cover the rescattering plateau and its cutoff. The data are compared with calculations based on a recent version of the molecular strong-field approximation, which was originally formulated for direct ionization and subsequently extended to include rescattering. (fast track communication)

[en] We have investigated dissociative ionization of N₂ and O₂ molecules by 52 nm extreme-ultraviolet light pulses at the free-electron laser facility in Japan. Distributions of kinetic energy release were measured at two different laser power densities below 3 x 10¹³ W cm^-2 and intermediate and final states of the sequential two photon transitions were identified. (fast track communication)

[en] We measured the angle-resolved High-order Above-Threshold Ionization spectroscopy of C₂H₄ and C₂H₆ with near-IR laser pulse, and extracted the electron-ion differential cross sections of those molecules from the electron spectroscopy by applying the quantitative rescattering theory. The differential cross sections show dramatically different distributions for C₂H₄ and C₂H₆, and this difference is believed to arouse from their different HOMO symmetry.

[en] Highlights: • We extracted DCSs of electron scattering from ions using electron spectroscopy. • Detail of the extraction procedure of DCS from the experiment is presented. • Experimentally extracted DCSs are compared with ab initio calculations. • Factorization model of rescattering is confirmed for molecules experimentally. - Abstract: We have measured angle-resolved rescattering photoelectron spectra of three small molecules (O₂, CO₂, and C₂H₄) using intense near-infrared laser pulses at several laser intensities. Based on the factorization formula for rescattering processes, we have extracted, from the electron spectra, the field-free differential cross sections of elastic electron scattering by the molecular ions. The detail of the extraction procedure is described. The experimentally extracted differential cross sections are compared with theoretical calculations of the field-free differential cross sections. Fairly good agreement between the experimentally extracted and theoretically calculated DCSs for wide range of the collision momentum indicates the validity of the present extraction procedure for the molecules