High harmonic generation (HHG) is an extremely nonlinear effect generating coherent
broadband radiation and pulse durations reaching attosecond timescales. Conventional …

In this review, we will focus on recent progress on the investigations of nondipole effects in
few-electron atoms and molecules interacting with light fields. We first briefly survey several …

Quantum optics with X-rays has long been a somewhat exotic activity, but it is now rapidly
becoming relevant as precision x-ray optics and novel X-ray light sources, and high-intensity …

A theory of above-threshold ionization of atoms by a strong laser field is formulated. Two
versions of the strong-field approximation (SFA) are considered, the direct SFA and the …

S-matrix theory of high-order harmonic generation (HHG) is generalized to multielectron
atoms. In the multielectron case the harmonic power is expressed via a coherent sum of the …

Time-resolved investigations of ultrafast electronic and molecular dynamics were not
possible until recently. The typical time scale of these processes is in the picosecond to …

Stimulated by the recent demonstration of the first bright source of circularly polarized high
harmonics, we examine the attosecond pulse trains generated by a group of such …

We resolve an open question about the origin of the giant enhancement in the high-
harmonic generation spectrum of atomic xenon around 100 eV. By solving the many-body …

The nonlinear Breit-Wheeler process is studied in the presence of strong and short laser
pulses. We show that for a relativistically intense plane-wave laser field many features of the …

We present a theory of high-order harmonic generation by a bichromatic elliptically
polarized laser field which consists of two coplanar components having the frequencies …