Momentum spirals in multiphoton pair production revisited

Abstract

Spirals in multiphoton pair production are revisited by two counterrotating fields with time delay for different cycles in pulse. Novel findings include that for subcycle fields; the remarkable spiral structure in the momentum spectrum can be still caused by a large time delay compared to the previous study for the supercycle case where it is easier to be generated by a small time delay. Also there exist a range of critical polarization values for the spirals' appearance corresponding to the different cycle numbers. The relative phase difference between two fields causes not only severe symmetry breaking of the momentum spectra pattern and spiral but also a significant change for the shape and the number of spiral arms. The number density is found to be more sensitive to the cycle number; in particular, it is enhanced by more than one order of magnitude for a small cycle pulse, while it is increased a few times when the time delay is small. These results provide an abundant theoretical testbed for the possible experimental observation of the multiphoton pair production in the future. Meanwhile, it is applicable to use the particles' momentum signatures as a new way to probe the laser field information.