Vortices in multiphoton pair production by two-color rotating laser fields

Vortex patterns in multiphoton pair creation by two-color elliptically polarized fields are investigated using the real-time Dirac-Heisenberg-Wigner formalism. For two-color circularly polarized fields with same or opposite helicities, we uncover both the vortices constituted of an even number of spirals and the ones with an odd number of spirals. The former corresponds to multiphoton pair creation by absorbing an odd (or even) number of photons from each rotating field, while the latter corresponds to multiphoton pair creation by absorbing an odd number of photons from one field and an even number of photons from the other one. This result is in agreement with qualitative theoretical analysis. For two-color elliptically polarized fields, vortex patterns are very sensitive to the ellipticity and a large ellipticity is required to detect vortices. This study provide a theoretical reference to observe multiphoton pair creation experimentally in future.