Strong-field ionization of atoms by circularly polarized femtosecond laser pulses produces a donut-shaped electron momentum distribution. Within the dipole approximation this distribution is symmetric with respect to the polarization plane. The magnetic component of the light field is known to shift this distribution forward. Here, we show that this magnetic nondipole effect is not the only nondipole effect in strong-field ionization. We find that an electric nondipole effect arises that is due to the position dependence of the electric field and which can be understood in analogy to the Doppler effect. This electric nondipole effect manifests as an increase of the radius of the donut-shaped photoelectron momentum distribution for forward-directed momenta and as a decrease of this radius for backwards-directed electrons. We present experimental data showing this fingerprint of the electric nondipole effect and compare our findings with a classical model and quantum calculations.
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http://dx.doi.org/10.1103/PhysRevLett.126.053202 | DOI Listing |
The electric dipole approximation is commonly adopted in the theoretical investigation of light-atom/molecule interaction, wherein the magnetic component of the driving electromagnetic field is neglected. Our study highlights the significant role of the magnetic field effect in the recollision dynamics of nonsequential double ionization (NSDI) driven by a mid-infrared laser. Due to the magnetic component of the laser field, in the multiple-returning events, the tunneling electron with a large initial momentum along the laser magnetic field direction at some specific tunneling time is inefficient for NSDI.
View Article and Find Full Text PDFPhys Rev Lett
February 2021
Institut für Kernphysik, Goethe-Universität, Max-von-Laue-Straße 1, 60438 Frankfurt, Germany.
Strong-field ionization of atoms by circularly polarized femtosecond laser pulses produces a donut-shaped electron momentum distribution. Within the dipole approximation this distribution is symmetric with respect to the polarization plane. The magnetic component of the light field is known to shift this distribution forward.
View Article and Find Full Text PDFJ Chem Theory Comput
October 2019
Department of Theoretical Chemistry and Biology , KTH Royal Institute of Technology, 10691 Stockholm , Sweden.
A methodology implemented to compute photoionization cross sections beyond the electric dipole approximation using Gaussian type orbitals for the initial state and plane waves for the final state is applied to molecules of various sizes. The molecular photoionization cross sections computed for valence molecular orbitals as a function of photon energy present oscillations due to the wave-like nature of both the outgoing photoelectron and of the incoming photon. These oscillations are damped by rotational and vibrational averaging or by performing a k-point summation for the solid state case.
View Article and Find Full Text PDFPhys Rev Lett
May 2007
Department of Physics and Astronomy, Eastern Michigan University, Ypsilanti, Michigan 48197, USA.
Nondipolar contribution to optical scattering in liquids and nanoparticle suspensions has been discerned for the first time from the dominant electric dipole scattering by assigning the observed polarization and azimuthal angular distribution of scattered polarized light to pure magnetic dipole and/or electric quadrupole radiation and ruling out other (the impurity of laser polarization, multiple scattering, optical activity, and optical anisotropy) explanations. The observed scattering has potential use in the optical study of nanoparticles.
View Article and Find Full Text PDFUltramicroscopy
February 2007
Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan 106, ROC.
Finite-difference time-domain (FDTD) technique simulations are performed to study the near-field resonance properties of a silver conical nano-tip with a rounded end. Varying the tip geometry, we have computed the electric field distribution, as well as the electric field enhancement factor in the immediate vicinity of the tip apex. The aim of this study is to find optimal geometric parameters of the conical tip, such as its angle and length, in order to maximize the electric field enhancement factor.
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