Biomedical subjects

L Avaldi

Publications and source records attributed to L Avaldi.

At least 19 recordsLinked to original sources

PubMed2006

Isolated single-cycle attosecond pulses.

We generated single-cycle isolated attosecond pulses around approximately 36 electron volts using phase-stabilized 5-femtosecond driving pulses with a modulated polarization state. Using a complete temporal characterization technique, we demonstrated the compression of the generated pulses for as low as 130 attoseconds, corresponding to less than 1.2 optical cycles. Numerical simulations of the generation process show that the carrier-envelope phase of the attosecond pulses is stable. The availability of single-cycle isolated attosecond pulses opens the way to a new regime in ultrafast physics, in which the strong-field electron dynamics in atoms and molecules is driven by the electric field of the attosecond pulses rather than by their intensity profile.

Journal Article↗

PubMed2006

Photodouble ionization dynamics for fixed-in-space H2.

The Coulomb explosion of the hydrogen molecule, after absorption of a 76 eV photon, has been studied by momentum imaging the two electrons and the two protons. Absolute fully differential cross sections of high statistical quality are obtained. A subset of the overall data, namely, equal electron-energy sharing, is used to investigate the effects of molecular orientation on the photoelectron angular distribution. Departures from the first-order helium-like model are evident in detection geometries where electron-electron correlation is "frozen."

Journal Article↗

PubMed2005

Effects of nuclear dynamics in the low-kinetic-energy Auger spectra of CO and CO2.

The CO and CO(2) carbon and oxygen Auger spectra have been measured by electron impact and compared with accurate theoretical calculations accounting for the effects of the dynamics of the nuclei on the energy and linewidth of the Auger bands. The calculations for CO were previously published [L. S. Cederbaum et al., J. Chem. Phys. 95, 6634 (1991)], while for CO(2) they are new and presented here for the first time. For both molecules, particular attention has been paid to the low-kinetic-energy region of the spectra, which corresponds to doubly charged ion states with the two holes mainly localized in the inner valence region. New bands have been observed. It is shown that a proper consideration of the vibrational broadening and shift of the bands due to the dynamics of the nuclei is needed to assign these features. For CO, very large energy shifts between corresponding features in the C 1s and O 1s spectra have been observed, confirming the theoretical predictions of 1991. The new computed spectra of CO(2) allow a very accurate analysis of the experiments over the whole energy range.

Journal Article↗

PubMed2003

Coherence of nondegenerate states studied by auger electron-photoelectron coincidence experiments in Kr.

The indirect double photoionization of Kr via the Kr+(3d(-1)(3/2,5/2)) states to the Kr2+(4s4p(5) (1)P(o)) final state has been studied by Auger electron-photoelectron angular resolved coincidence experiments. By tuning the incident photon energy, we succeeded in observing the coherence in the photoionization of two nondegenerate spin-orbit states. The observations have been described quantitatively by a model which accounts for the two pathways to the final state as well as for the indistinguishability of the two ejected electrons.

Journal Article↗

PubMed2001

Experimental observation of post-collision interaction and interference effects in resonant double photoionization processes.

The combined effects of post-collision interaction in the final state and interference due to the indistinguishability of the two electrons have been studied in a selected case of resonant double photoionization of neon. In our coincidence experiments, the photo- and Auger-electron pair was measured when the two electrons have nearly equal energy and are ejected at small mutual angle. The obtained energy distributions exhibit a strong interplay of post-collision interaction and interference effects, in agreement with the theoretical prediction of Sheinerman and Schmidt [J. Phys. B 30, 1677 (1997)] made on beryllium.

Journal Article↗

PubMed2000

Observation and characterization of the fluorescence decay of the 2s2p(6)np 1P(o) excited states of Ne

Fluorescence decay of the 2s2p(6)np (1)P(o) excited states of neon has been observed directly for the first time. This process has also been observed indirectly by threshold photoelectron spectroscopy and in electron/photon coincidences. The measurements have allowed this weak decay channel to be characterized and branching ratios derived. The fluorescence excitation spectrum is well described by a simple Rydberg model that highlights the interplay and competition between the decay channels of autoionization and fluorescence.

Journal Article↗

PubMed1998

The gas-phase photoemission beamline at Elettra.

This paper reports the present stage of commissioning of the gas-phase photoemission beamline at Elettra, Trieste. The beamline is designed for atomic and molecular science experiments with high-resolution and high-flux synchrotron radiation. It consists of an undulator source, variable-angle spherical-grating monochromator and two experimental stations. The design value of the energy range is 20 to 800 eV with a specified resolving power of over 10000. The procedure adopted for calibration of this type of monochromator is discussed. At present a resolving power up to 20000 and a range up to 900 eV have been measured. Absorption spectra taken at the argon L(II,III)-edge and at the nitrogen, oxygen and neon K-edges are as sharp as, or sharper than, any reported in the literature. The instrumental broadening is well below the natural line-width making it difficult to quantify the resolution; this problem is discussed.

Journal Article↗

PubMed1996