Momentum Vortices on Pairs Production by Two Counter-Rotating Fields

The momentum signatures of created pairs in the multiphoton regime in strong fields are investigated and obvious vortex patterns that are constituted of the quasi-Archimedian spirals are found when considering two opposite-handedness circularly polarized fields. Distinguished from the familiar Ramsey interference fringes with the concentric rings under two identical-handedness fields, however, the finding vortices are associated to the interference between the pair production amplitudes of these two opposite-handedness fields. Moreover, the sensitive dependence of vortex patterns on the relative carrier envelope phase, the time delay, and the handedness between two fields imply also a new way to detect the applied laser field characteristics.