Vortices in multiphoton pair production revisited

Vortices in multiphoton pair production are revisited by two counter-rotating fields with time delay for different cycles in pulse. Novel findings include that for subcycle fields, the remarkable vortex structure in the momentum spectrum can be still caused by a large time delay compared to the previous study for supercycle case where it is easier to be generated by a small time delay. And also there exist a range of critical polarization values for the vortices appearance corresponding to the different cycle number. The relative phase difference between two fields causes not only severe symmetry breaking of the momentum spectra pattern and vortex, but also a significant change for the shape and the number of vortex spiral. Upon the number density, it is found a more sensitive to the cycle number, in particularly, it is enhanced by more than one order of magnitude for small cycle pulse, while it is increased about few times when the time delay is small. These results provide an abundant theoretical testbed for the possible experimental observation on the multiphoton pair production in future. Meanwhile, it is applicable to regard the particles momentum signatures as a new probing to the laser field information with it from the vacuum.Comment: 29 pages, 12 figures, 2 table

Schwinger pair production rate and time for some space-dependent fields via worldline instantons formalism

Schwinger pair production rate and time in some space-dependent fields are studied analytically by using the worldline instantons formalism. The instanton path, action, production rate, vacuum-decay time and tunneling time are obtained, which depend on the Keldysh parameter significantly. It is found that under a given field the instanton paths with different Keldysh parameter are exactly in the same plane. Moreover, the normalized instanton actions are all bounded within the region from $$\pi$$ to $$2\pi$$. We also find the relationship between vacuum-decay time and tunneling time. Graphic abstract: Schwinger pair production rate and time in some space-dependent fields are studied analytically by using the worldline instantons formalism. The instanton path, action, production rate, vacuum-decay time and tunneling time are obtained, which depend on the Keldysh parameter significantly. It is found that under a given field the instanton paths with different Keldysh parameter are exactly in the same plane. Moreover, the normalized instanton actions are all bounded within the region from $$\pi$$ to $$2\pi$$. We also find the relationship between vacuum-decay time and tunneling time