A. Diner

Electrostatic ion beam trap for electron collision studies

We describe a system combining an ion beam trap and a low energy electron target in which the interaction between electrons and vibrationally cold molecular ions and clusters can be studied. The entire system uses only electrostatic fields for both trapping and focusing, thus being able to store particles without a mass limit. Preliminary results for the electron impact neutralization of C2− ions and aluminum clusters are presented.

Near-threshold high-order harmonic spectroscopy with aligned molecules.

We study high-order harmonic generation in aligned molecules close to the ionization threshold. Two distinct contributions to the harmonic signal are observed, which show very different responses to molecular alignment and ellipticity of the driving field. We perform a classical electron trajectory analysis, taking into account the significant influence of the Coulomb potential on the strong-field-driven electron dynamics. The two contributions are related to primary ionization and excitation processes, offering a deeper understanding of the origin of high harmonics near the ionization threshold. This Letter shows that high-harmonic spectroscopy can be extended to the near-threshold spectral range, which is in general spectroscopically rich.

Size effects in the interaction between ionic clusters and low-energy electrons

The interaction between size specific negative clusters (Cn−, 1 < n < 12, Agn−, 1 < n < 11) and low-energy electrons has been studied using a new experimental setup where the ionic clusters are first cooled to room temperature in an electrostatic ion trap. The electron impact detachment cross-sections were measured for electron energies between 5 and 30 eV. The results are analysed in terms of a classical model.

Electrostatic ion beam trap

The conventional way of trapping ions is based on the uses of RF or magnetic fields, like in Paul or Penning traps. In such traps the ions are stored with approximately zero kinetic energy. In many applications a well-defined ion beam is needed especially in collision experiment, where the initial direction of a beam is critical for reaction product measurements and a well defined field free region is required at the collision place. In the last few years we have developed a new type of electrostatic ion trap for ion beams of a few keV per charge, with no mass limit. The ions are injected through a stack of electrodes, which are used as an electrostatic mirror. The ions are confined in a region of few tens of centimeters by two electrostatic mirrors, located on opposite sides. The stability criterion of such a trap can be demonstrated to be similar to the one existing for optical resonator. The dynamics of such trapped ion beam was studied for various potentials on the electrostatic mirrors. Two modes of operation were found. In the first mode a self bunching effect was observed where the ion-ion Coulomb interaction generates a single bunch with constant length along the whole trapping time. This mode of operation can be used for Fourier mass spectrometry. A second mode, where the Coulomb interaction enhances the correlation between the ion position and momentum, enables phase space manipulation of the stored ion beam.

Photodissociation of H2+ by intense chirped pulses – beyond the effect of pulse duration and peak power

H2+ photodissociation, induced by intense short laser pulses, was measured by a full 3D imaging system. We have conducted a series of experiments, in which we systematically changed the linear chirp, using a pulse shaper, and observed the kinetic energy release spectra(KER). Distinct differences in the KER spectra are observed both in peak positions and angular distribution for laser pulses with similar duration and intensity but opposite chirp sign.

Near-Threshold High-Order Harmonic Spectroscopy with Aligned Molecules

We study HHG close to the ionization threshold and identify two distinct contributions to the emitted harmonic signals. The observed near-threshold emission is shown to occur outside the realm of the standard strong field approximation.

Below-Threshold High-Order Harmonics Probed with Aligned Molecules

We present a new approach to probe the High-Harmonic Generation process. We use aligned molecules to study below-threshold harmonics and identify two distinct contributions to the emitted harmonics.