Mapping the direction of electron ionization to phase delay between VUV and IR laser pulses

Abstract

We theoretically demonstrate a one-to-one mapping between the direction of electron ionization and the phase delay between a linearly polarized vacuum ultraviolet (VUV) and a circular infrared (IR) laser pulse. To achieve this, we use an ultrashort VUV pulse that defines the moment in time and space when an above-threshold electron is released in the IR pulse. The electron can then be accelerated to high velocities escaping in a direction completely determined by the phase delay between the two pulses. The dipole matrix element to transition from an initial bound state of the N 2 molecule, considered in this work, to the continuum is obtained using quantum-mechanical techniques that involve computing accurate continuum molecular states. Following release of the electron in the IR pulse, we evolve classical trajectories, neglecting the Coulomb potential and accounting for quantum interference, to compute the distribution of the direction and magnitude of the final electron momentum. The concept we theoretically develop can be implemented to produce nanoscale ring currents that generate large magnetic fields.

Streaking single-electron ionization in open-shell molecules driven by X-ray pulses

“…where Y lm is a spherical harmonic and P lm is the radial part of the wavefunction. To obtain the continuum wavefunction, we solve a system of Hartree-Fock (HF) equations [5,17]. Note that we fully account for the Coulomb potential.…”

“…For details on the computation of a( p f ), see Ref. [5]. We compute a( p f ) classically using the quantum expression we obtain for D M .…”

“…As mentioned above, we obtain the continuum wavefunction by solving a system of HF equations [5,17,32] given by…”

“…These streaking experiments are typically performed in the low IR intensity limit. However, it has been demonstrated that at higher IR intensities, the properties of the IR field dominate the final momentum distribution and the IR field controls the electron motion [5]. Recently, there has been substantial effort to extend the streaking methodology to X-ray free electron laser (XFEL) sources, which provide a source of high intensity X-ray pulses, for the purpose of characterizing the temporal structure of the X-ray pulse [6][7][8].…”