Effects of polarization and high harmonics of two-color fields on dynamically assisted pair production

Abstract: Electron-positron pair production in dynamically assisted two-color electric fields is investigated for various polarizations. Momentum spectrum and number density of the created pairs are examined carefully, in particular, the effects of polarization and high harmonics of two-color fields are exhibited. For only single strong field, the interference effects of momentum spectrum would vanish when polarization is high, however, for the dynamical assisted two-color fields, the interference effects would be more and more remarkable with polarization. The multiple peaks of momentum spectrum in elliptic or/and circular polarization are observed and explained. It is found that there exists a strong nonlinear dependence of the number density on the high harmonics of two-color fields, for example, the number density can be enhanced significantly over $7-8$ orders when appropriate high harmonics is present. Another interesting finding is that the polarization effect on number density is gradually weaken as the high harmonics increases, however, a weak nonlinearity relation appears again if the high harmonics exceeds a single-photon threshold.