We show that the electrons, produced in strong-bicircular-field-induced above-threshold ionization of inert-gas atoms, have a large spin asymmetry if the ions exhibit fine-structure splitting. For a bicircular field, which consists of two coplanar counterrotating circularly polarized fields of frequencies $\omega$ and $2\omega$, the spin-asymmetry parameter changes rapidly with the electron energy. Since the electron–parent-ion rescattering in a counterrotating bicircular field is characterized on the attosecond time scale, this spin asymmetry may introduce the spin degree of freedom into attoscience. We show that the high-energy backward and low-energy forward scattered electrons, which are produced on the scale of a fraction of the laser cycle, exhibit spin asymmetry.

• Received 5 January 2016

DOI:https://doi.org/10.1103/PhysRevA.93.051402