Carrier-envelope phase and pulse-shape effects on vacuum pair production in asymmetric electric fields with bell-shaped envelopes

We investigate the combined effects of carrier-envelope phase and laser pulse shape on electron-positron pair production in the presence of an external time-dependent asymmetric electric field by solving the quantum Vlasov equation. We analyze how the pulse asymmetry, the envelope type (Gaussian, Lorentzian, and Sauter), and the carrier-envelope phase jointly influence the momentum distribution and the total number of produced pairs per unit volume. Our results show that pair production exhibits extreme sensitivity to both the degree of the temporal asymmetry and the steepness of the envelope on either side of the pulse. These effects are qualitatively explained through a turning-point analysis for the nonanalytic electric field using a regularization scheme. We observe that multiphoton pair production dominates the Schwinger mechanism in the case of a long falling-pulse asymmetry. For a short falling pulse with a flat-topped profile, pair production is further facilitated. We demonstrate that the density of produced pairs can be enhanced by two to three orders of magnitude by choosing certain field parameters.