Non-Sequential Double Ionization of Ne in Intense Laser Pulses: A Coincidence Experiment

The dynamics of Neon double ionization by 25 fs, 1.0 PW/cm2 laser pulses at 795 nm has been studied in a many particle coincidence experiment. The momentum vectors of all ejected atomic fragments (electrons and ions) have been measured using combined electron and recoil-ion momentum spectroscopy. Electron emission spectra for double and single ionization will be discussed. In both processes the mean electron energies differ considerably and high energetic electrons with energies of more than 120 eV have been observed for double ionization. The experimental results are in qualitative agreement with the rescattering model

Separation of Recollision Mechanisms in Nonsequential Strong Field Double Ionization of Ar: The Role of Excitation Tunneling

Vector momentum distributions of two electrons created in double ionization of Ar by 25 fs, 0.25PW/cm2 laser pulses at 795 nm have been measured using a “reaction microscope.” At this intensity, where nonsequential ionization dominates, distinct correlation patterns are observed in the two-electron momentum distributions. A kinematical analysis of these spectra within the classical “recollision model” revealed an (e,2e)-like process and excitation with subsequent tunneling of the second electron as two different ionization mechanisms. This allows a qualitative separation of the two mechanisms demonstrating that excitation-tunneling is the dominant contribution to the total double ionization yield

Laserspektroskopische Untersuchungen an hochangeregten Rydberg Zustaenden des atomaren und molekularen Wasserstoffs

Rottke H. Laserspektroskopische Untersuchungen an hochangeregten Rydberg Zustaenden des atomaren und molekularen Wasserstoffs. Bielefeld; 1986

Wenn Licht Atome in Stücke reißt

Mit gepulsten Lasern lassen sich heute für wenige Femtosekunden Lichtintensitäten von mehr als 1018 W/cm2 erzeugen. Dabei werden elektrische Feldstärken von 1010 V/cm erreicht, vergleichbar mit den Feldern, die Elektronen in Atomen binden. Wie verhalten sich Atome unter solch extremen Bedingungen? Während auf der einen Seite Wechselwirkungen von extremen Laserfeldern mit Materie schon heute viele Anwendungen haben, etwa in der Medizin oder der Materialbearbeitung, sind auf der anderen Seite immer noch viele der fundamentalen Fragen dieser Wechselwirkung ungeklärt. Insbesondere stellt sich eines der ältesten Probleme der Quantenmechanik, das Mehrteilchenproblem, von Neuem: wie verhalten sich Mehrelektronensysteme in starken Feldern? Aufschluss darüber erlauben neue Experimente, die erstmals die Impulse von Ionen und Elektronen aus der Mehrfachionisation von Atomen in Laserfeldern sichtbar machen

Probing electron and hole co-localization by resonant four-wave mixing in the extreme-ultraviolet

The extension of nonlinear spectroscopic techniques into the x-ray domain is in its infancy but holds the promise to provide unique insight into the dynamics of charges in photoexcited processes, which are of fundamental as well as applied interest. We report on the observation of a third order nonlinear process in lithium fluoride at a free-electron laser. Exploring the yield of four wave mixing (FWM) in resonance with transitions to strongly localized core exciton states vs. delocalized Bloch states, we find resonant FWM to be a sensitive probe for the degree of charge localization: substantial sum- and difference-frequency generation is observed exclusively when in a one- or three-photon resonance with a LiF core exciton, with a dipole forbidden transition affecting details of the nonlinear response. Our reflection-geometry-based approach to detect FWM signals enables the study of a wide variety of condensed matter sample systems, provides atomic selectivity via resonant transitions and can be easily scaled to shorter wavelengths at free electron x-ray lasers

Probing electron and hole co-localization by resonant four-wave mixing in the extreme-ultraviolet

The extension of nonlinear spectroscopic techniques into the x-ray domain is in its infancy but holds the promise to provide unique insight into the dynamics of charges in photoexcited processes, which are of fundamental as well as applied interest. We report on the observation of a third order nonlinear process in lithium fluoride at a free-electron laser. Exploring the yield of four wave mixing (FWM) in resonance with transitions to strongly localized core exciton states vs. delocalized Bloch states, we find resonant FWM to be a sensitive probe for the degree of charge localization: substantial sum- and difference-frequency generation is observed exclusively when in a one- or three-photon resonance with a LiF core exciton, with a dipole forbidden transition affecting details of the nonlinear response. Our reflection-geometry-based approach to detect FWM signals enables the study of a wide variety of condensed matter sample systems, provides atomic selectivity via resonant transitions and can be easily scaled to shorter wavelengths at free electron x-ray lasers