Spin polarization by strong field ionization

Fig. 1 Spin polarization measured as a function of the electron energy. The blue curve is a theoretical prediction, while the red points with error bars show the experimental results. The measurement was carried out for Xe atoms.

This situation has now changed with the joint experimental and theoretical work of Alexander Hartung et al., Inspired by the earlier theoretical prediction of I. Barth and O. Smirnova (Phys. Rev. A 88, 013401, 2013). Using gas from Xe atoms, the authors present the first experimental evidence of electron spin polarization generated by strong field ionization. The measured spin polarization, see Figure 1, reached values ​​up to 30% high, reversing their sign with the electron energy. This work opens up the new dimension of spin in the field of strong field physics. It paves the way for the generation of sub-femtosecond, spin-polarized electron pulses with numerous applications, ranging from the study of magnetic properties of matter on ultrafast time scales to the testing of chiral molecular systems with sub-femtosecond time and sub-angstrom spatial resolution. The publication also shows that spin polarization during laser-driven electron recombination with the parent ion is important when such a collision is induced by an elliptical laser field. Since the electron is completely controlled by the laser field during the laser-driven electron collision with the parent ion, the dynamics can now be studied not only with attoseconds of temporal and angstrom spatial resolution, but also with spin sensitivity. This would allow investigating chiral molecules with sub-femtosecond time resolution and sub-angstrom spatial resolution. Finally, the spin polarization of the liberated electron is tightly bound to the generation of the parent ion in an initial spin-polarized state. Spin-orbit coupling then leads to internal annular electron and spin currents.