Abstract
We have applied a tomographic imaging method to recreate the full three-dimensional distribution of photoelectrons produced in a strong-field photodetachment process. The method is general and can be applied to any laser polarization. This stands in contrast to traditional imaging inversion methods, such as Abel inversion, which require prior knowledge of the symmetries of the electron distribution and are therefore limited to experiments using linear or circular polarization. Our method is also useful in a situation where linear polarization is used, since it compensates for detector inhomogeneities by spreading the information on a larger detector surface. In addition, it facilitates a method to detect polarization defects. Measurements were made for photodetachment of ${\mathrm{Ag}}^{\ensuremath{-}}$ at laser wavelengths of 1310 and 2055 nm, and were found to agree well with simulations in the strong field approximation. The data in the 1310 nm case revealed an unexpected asymmetry in the plane in which the laser polarization axis is rotated. Using a quasistationary quasienergy state model, a residual elliptical polarization of $\ensuremath{\varepsilon}=0.21\ifmmode\pm\else\textpm\fi{}0.01$ consistently explains the observed asymmetry. We conclude that the method described in this paper has the potential to be applied in experiments where a more complete characterization of electron emission distributions is required.
Highlights
Electron imaging has become an ubiquitous tool to record the momentum and angular distribution of electrons emitted in photoionization and photodetachment processes [1]
Our results show an unexpected feature in an asymmetry of the photoelectron distribution in the polarization plane of the laser field
We have implemented a tomographic imaging method to recreate the full three-dimensional distribution of photoelectrons produced in a strong-field photodetachment process
Summary
Electron imaging has become an ubiquitous tool to record the momentum and angular distribution of electrons emitted in photoionization and photodetachment processes [1]. On the other hand, a cylindrically symmetric spatial distribution appears around the laser propagation axis. In both cases, a position-sensitive detector located in a plane parallel to these selected axes can be used to record an image of charged particle impacts which is twofold symmetric, with one symmetry axis along the selected axis of projection and one along an axis perpendicular to it. When electron emission is preferentially parallel to the laser polarization (such as is generally the case in strong electromagnetic fields), conventional inversion routines produce distortions since single-image inversion causes an accumulation of inversion errors along the axis of symmetry. In a traditional photoelectron imaging experiment, this asymmetry would not be visible, which shows that the sensitivity of the tomographic method makes it useful in cases where standard imaging methods are normally employed
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