E V Gryzlova

Coherent control with a short-wavelength free-electron laser

Researchers demonstrate correlation of two colours (63.0 and 31.5 nm wavelengths) in a free-electron laser and control photoelectron angular distribution by adjusting phase with 3 attosecond resolution.

Angular distributions and angular correlations in sequential two-photon double ionization of atoms

A general expression for the angular correlation function of the two emitted photoelectrons in sequential two-photon double ionization of atoms is derived and discussed. The expression can be used in the analysis of angle-resolved coincidence experiments. The angular distributions of the emitted electrons as measured in non-coincidence experiments are also discussed. As an example, the cross sections, angular distributions of photoelectrons and angular correlation functions for the sequential two-photon double ionization of Ne and Ar atoms have been calculated within the MCHF and MCDF approaches. The results are compared with recent experiments performed at the free-electron laser (FLASH) facility.

Photoelectron spectroscopy of sequential three-photon double ionization of Ar irradiated by EUV free-electron laser pulses

We have investigated the ionization of the Ar atom by 51 nm extreme-ultraviolet light pulses at the free-electron laser facility, SPring-8 Compact SASE Source test accelerator, in Japan. The angle-resolved photoelectron spectra contain lines due to sequential three-photon double ionization with the second ionization step proceeding via the resonantly enhanced two-photon absorption. The relative intensities of the corresponding photoelectron peaks and their angular dependence are explained in the framework of a three-step model of the process.

Sequential two-photon double ionization of Kr atoms

Sequential two-photon double ionization of Kr atoms is theoretically considered. The angular distribution of emitted electrons is calculated with the dipole amplitudes evaluated within the multiconfigurational Hartree–Fock and Dirac–Fock approaches. The difference in angular distributions for two-photon and single-photon ionization is discussed.

Sequential two-photon double ionization of the 4d shell in xenon

The sequential two-photon double ionization of 4d electrons of xenon in intense free-electron laser (FEL) radiation is theoretically investigated for photon energies of 70–200 eV. At these energies, which are available at the free-electron laser FLASH, the 4d photoionization dominates over the ionization of the valence shells, showing a giant resonance. The 4d vacancy produced by the first photon strongly couples to the (Auger) autoionization continuum with a lifetime of only ~6 fs and thus the Auger decay competes with the second photoionization in a typical FEL pulse. The photoelectron angular distributions and angular correlation between emitted electrons are investigated as associated with the peculiar 4d character of the photoionization and Auger decay.

Angular correlations between two electrons emitted in the sequential two-photon double ionization of atoms

Angular correlations between two emitted photoelectrons in the sequential two-photon double ionization (TPDI) of atoms are theoretically considered. The general expression for the angular correlation function is analysed and some particular geometries of possible experiments are discussed. The concept of true angular correlations is introduced in contrast to the angular dependence of the two-electron emission from two uncorrelated ionization events. The case of a pure LS coupling description of the TPDI is considered in detail and compared with the general case. As an example, calculations of the angular correlation functions are performed and discussed for sequential TPDI from the 4p valence shell of krypton.

Non-dipole effects in the angular distribution of photoelectrons in sequential two-photon atomic double ionization

Motivated by the recent achievements of experiments using x-ray free electron lasers, we have developed a theory for the angular distributions of photoelectrons in sequential two-photon double ionization (2PDI) of atoms beyond the dipole approximation. Expressions for the angular distributions are obtained taking into account the full multipole expansion of radiation in electric and magnetic moments. The formalism is further specified for the first-order corrections to the dipole approximation. As an illustrative example, the sequential 2PDI of the 2p shell in atomic neon is studied. The numerical calculations predict distinct non-dipole effects observable in experiments at present x-ray free electron lasers.

Effects of fullerene confining potential on the ionization of the hydrogen atom by a strong femtosecond VUV pulse

Ionization of atoms trapped inside a fullerene cage by femtosecond VUV pulses is studied beyond the perturbative regime. When solving the time-dependent Schrodinger equation, the cage surrounding the hydrogen atom is modelled by a spherical square-well potential with the parameters corresponding to the fullerenes C60 and C36. The influence of the cage on the yields and angular distributions of electrons in the main and first ATI lines is revealed for ionization from the ground 1s and metastable 2s states.

New possibilities of X-ray nanocrystallography of biological macromolecules based on X-ray free-electron lasers

X-ray serial nanocrystallography is a new technique for determining the three-dimensional structure of biological macromolecules from data on the diffraction of ultrashort pulses generated by X-ray free-electron lasers. The maximum achievable resolution for a set of experimental data as a function of the sample sizes and parameters of the equipment is estimated based on simulations of the diffraction process with allowance for changes in the electronic structure of the atoms of the sample under the influence of X-rays. Estimates show that nanocrystallography greatly enhances the possibilities of X-ray analysis, reducing the requirements for the minimum permitted size of the crystals and enabling to explore poorly crystallizable molecular objects, such as many membrane proteins and complexes of macromolecules.

Sequential two-photon double ionization of noble gases by circularly polarized XUV radiation

Photoelectron angular distributions (PADs) and angular correlations between two emitted electrons in sequential two-photon double ionization (2PDI) of atoms by circularly polarized radiation are studied theoretically. In particular, the sequential 2PDI of the valence shell in noble gas atoms (neon, argon, krypton) is analyzed, accounting for the first-order corrections to the dipole approximation. Due to different selection rules in ionization transitions, the circular polarization of photons causes some new features of the cross sections, PADs and angular correlation functions in comparison with the case of linearly polarized photons.