The combination of high-order harmonic generation (HHG) with resonant XUV excitation of a core electron into the transient valence vacancy that is created in the course of the HHG process is investigated theoretically. In this setup, the first electron performs a HHG three-step process, whereas the second electron Rabi flops between the core and the valence vacancy. The modified HHG spectrum due to recombination with the valence and the core is determined and analyzed for krypton on the 3d→4p resonance in the ion. We assume an 800 nm laser with an intensity of about 10(14) W/cm2 and XUV radiation from the Free Electron Laser in Hamburg (FLASH) with an intensity in the range 10(13)-10(16)W cm2. Our prediction opens perspectives for nonlinear XUV physics, attosecond x rays, and HHG-based spectroscopy involving core orbitals.
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"energies by the former resonance energy with respect to the first plateau ( Buth et al . , 2011 ) . The presence of originally two bound electrons is thereby crucial for the effect . Plateau extension in the presence of two electrons has already been noticed in Koval et al . ( 2007 ) , however , with a low probability of the secondary plateau . In Buth et al . ( 2011 ) , the intensity of the secondary plateau is tunable via the FEL intensity . A schematic of the proposed scheme is shown in Fig . 11 . The atoms are irradiated by both an intense optical laser field and the resonant x - ray field from an FEL . As soon as the valence electron Fig . 11 . ( Color online ) Schematic of the HHG scenario as "
[Show abstract][Hide abstract] ABSTRACT: In the past two decades high-harmonic generation (HHG) has become a key
process in ultra-fast science due to the extremely short time-structure of the
underlying electron dynamics being imprinted in the emitted harmonic light
bursts. After discussing the fundamental physical picture of HHG including
continuum--continuum transitions, we describe the experimental progress
rendering HHG to the unique source of attosecond pulses. The development of
bright photon sources with zeptosecond pulse duration and keV photon energy is
underway. In this article we describe several approaches pointed toward this
aim and beyond. As the main barriers for multi-keV HHG, phase-matching and
relativistic drift are discussed. Routes to overcome these problems are pointed
out as well as schemes to control the HHG process via alterations of the
driving fields. Finally, we report on how the investigation of fundamental
physical processes benefits from the continuous development of HHG sources.
Full-text · Article · Jan 2012 · Advances in Atomic, Molecular, and Optical Physics
"For both presented schemes, we fnd substantial HHG yield for the recombination of the continuum electron with the core hole. Our prediction ofers novel prospects for nonlinear x-ray physics, attosecond x rays, and timeresolved chemical dynamics  . "
[Show abstract][Hide abstract] ABSTRACT: X-ray science is undergoing one of its greatest revolutions to date with the construction of intense x-ray free electron lasers (FELs) in Menlo Park, California, USA (LCLS), Hamburg, Germany (European XFEL), and Harima Science Garden City, Japan (SACLA). These are vast, several-hundred-million dollar machines that provide x-ray pulses that are many million times brighter than current sources. Similarly groundbreaking are the emerging attosecond light sources based on intense, pulsed optical lasers; they are relatively inexpensive laboratory-size instruments. These two emerging radiation sources enable radically new research and have unnumbered potential applications in materials science, chemistry, biology, and physics. Our work aims at bringing the capabilities of HHG-based attosecond sources to FELs [1,2]. First, we theoretically combine high-order harmonic generation (HHG) with resonant x-ray excitation of a core electron into the transient valence vacancy that is created in the course of the HHG process: the frst electron performs a HHG three-step process whereas, the second electron Rabi fops between the core and the transient valence vacancy [Fig. 1]. The modifed HHG spectrum due to recombination with the valence and the core is determined and analyzed —for krypton  on the 3d → 4p resonance [Fig. 2] and for neon  on the 1s → 2p—in the respective cations in the light of an optical laser and an FEL. Second, we examine HHG where tunnel ionization (frst step) is replaced by direct x-ray ionization of core electron of neon. We use the boosted HHG radiation to predict single attosecond pulses in the kiloelectronvolt regime. For both presented schemes, we fnd substantial HHG yield for the recombination of the continuum electron with the core hole. Our prediction ofers novel prospects for nonlinear x-ray physics, attosecond x rays, and time-resolved chemical dynamics [1,2].
[Show abstract][Hide abstract] ABSTRACT: A theoretical model is developed describing high-order harmonic generation
(HHG) from a gas of multiply-charged ions driven by a laser field of
relativistic intensity. Macroscopic propagation of harmonics is investigated in
a relativistic HHG setup where the relativistic drift is suppressed by means of
x-ray field assistance of the driving laser field. The possibility of
phase-matched emission of the harmonics is shown. The laser field geometry is
optimized to maximize the HHG yield with the corresponding phase-matching
schemes. Crucial issues determining the macroscopic HHG yield are discussed in
Full-text · Article · Nov 2011 · Physical Review A