Back-to-back emission of the electrons in double photoionization of helium

TL;DR

This paper analyzes high-energy double photoionization of helium, confirming the quasifree mechanism through experimental data, revealing back-to-back electron emission, and highlighting the role of quadrupole interactions in electron dynamics.

Contribution

It provides the first experimental confirmation of the quasifree mechanism in double photoionization, emphasizing the significance of quadrupole terms in electron emission patterns.

Findings

Experimental evidence of back-to-back electron emission.

Confirmation of the quasifree mechanism in helium ionization.

Identification of quadrupole interaction effects.

Abstract

We calculate the double differential distributions and distributions in recoil momenta for the high energy non-relativistic double photoionization of helium. We show that the results of recent experiments is the pioneering experimental manifestation of the quasifree mechanism for the double photoionization, predicted long ago in our papers. This mechanism provides a surplus in distribution over the recoil momenta at small values of the latter, corresponding to nearly "back-to-back" emission of the electrons. Also in agreement with previous analysis the surplus is due to the quadrupole terms of the photon-electron interaction. We present the characteristic angular distribution for the "back-to-back" electron emission. The confirmation of the quasifree mechanism opens a new area of exiting experiments, which are expected to increase our understanding of the electron dynamics and of the bound states structure. The results of this Letter along with the recent experiments open a new field for studies of two-electron ionization not only by photons but by other projectiles, e.g. by fast electrons or heavy ions.