We present the first circularly polarized harmonics in the soft X-ray region and the physics underlying it. This source enables the first X-ray magnetic circular dichroism measurements in rare earth elements on tabletop.

The tuning of odd and even high-order harmonics along the resonances of laser-produced plasmas using an optical parametric amplifier of white-light continuum radiation (1250–1400 nm)and its second harmonic is reported. We demonstrate the enhancement of tunable harmonics in the regions of 27, 38, and 47 nm using tin, antimony, and chromium plasmas and discuss the theoretical model of this phenomenon.

Strong-field ionization in two-color circularly polarized fields is studied, where both experimental measurements and theoretical analyses suggest that the production of high-energy electrons from electron-ion rescattering is optimized in counterrotating fields, and when the ponderomotive energies of the two laser fields are equal.

We show that the electrons, produced in strong-bicircular-field-induced above-threshold ionization of inert-gas atoms, have a large spin asymmetry if the ions exhibit fine-structure splitting. For a bicircular field, which consists of two coplanar counterrotating circularly polarized fields of frequencies $\ensuremath{\omega}$ and $2\ensuremath{\omega}$, the spin-asymmetry parameter changes rapidly with the electron energy. Since the electron--parent-ion rescattering in a counterrotating bicircular field is characterized on the attosecond time scale, this spin asymmetry may introduce the spin degree of freedom into attoscience. We show that the high-energy backward and low-energy forward scattered electrons, which are produced on the scale of a fraction of the laser cycle, exhibit spin asymmetry.

Nonlinear quantum-mechanical phenomena in strong laser fields, such as high-order harmonic generation (HHG) and above-threshold ionization (ATI) are significantly modified if the applied laser field is bichromatic and/or elliptically polarized. Numerical results obtained within the strong-field approximation are presented for two special cases. We show results for HHG by plasma ablation in a bichromatic linearly polarized laser field. We also consider the ATI process in bicircular field which consists of two coplanar counter-rotating circularly polarized fields.

The dynamics of the interaction between intense laser field and one-electron molecule H2+ is investigated by solving three-dimensional time-dependent Schrodinger equation (3D TDSE) in the Born-Oppenheimer approximation. It is assumed that the laser field is polarized along the internuclear axis. The wave function is expanded in finite series using B-spline functions and spherical harmonics in prolate spheroidal coordinates. The results for the high-order harmonic generation and above-threshold ionization are presented.

We investigate high-order above-threshold ionization (HATI) of krypton atoms by a bicircular laser field, which consists of two coplanar co- or counter-rotating circularly polarized fields of frequencies rw and sw. We show that the photoelectron spectra in the HATI process, presented in the momentum plane, exhibit the same discrete rotational symmetry as the driving field. We also analyze HATI spectra for various combinations of the intensities of two field components for co- and counter-rotating fields. We find that the appearance of high-energy plateau for the counter-rotating case is vary sensitive to the laser intensity ratio, while the plateau is always absent for the co-rotating bicircular field.

We present the first circularly polarized soft X-ray harmonics to photon energies >160eV. Bright phase matched beams are used to characterize important materials with intrinsic perpendicular magnetic anisotropy on tabletop for the first time

We investigate laser-assisted electron-ion recombination (LAR), high-order harmonic generation (HHG) and above-threshold ionization (ATI) of argon atoms by a bicircular laser field, which consists of two coplanar counter-rotating circularly polarized fields of frequencies rω and sω. The energy of soft x rays generated in the LAR process is analyzed as a function of the incident electron angle and numerical results of direct recombination of electrons with Ar+ ions are presented. We also present the results of HHG by a bicircular field and confirm the selection rules derived earlier for inert-gas atoms in a p ground state. We show that the photoelectron spectra in the ATI process, presented in the momentum plane, as well as the LAR spectra exhibit the same discrete rotational symmetry as the applied field.

A recently developed unified description of low-order above-threshold ionization (Becker et al 2014 J. Phys. B: At. Mol. Opt. Phys. 47 204022; 2015 J. Phys. B: At. Mol. Opt. Phys. 48 151001) is revisited and extended. By considering the rescattering electron energies and angles at the classical cutoffs and the contributions of particular quantum-orbit solutions, it is shown that summing both the backward- and the forward-scattering contributions, within the low-frequency approximation, it is possible to reproduce the observed features of the ATI spectra both for low and high energies and both on and off the laser-polarization axis in the momentum plane.