Photoproduction of electron–positron pairs by the strong-field Breit–Wheeler process in an intense laser field is studied. The laser field is assumed to consist of two consecutive short pulses, with a variable time delay in between. By numerical calculations within the framework of scalar quantum electrodynamics, we demonstrate that the time delay exerts a strong impact on the pair-creation probability. For the case when both pulses are identical, the effect is traced back to the relative quantum phase of the interfering S-matrix amplitudes and explained within a simplified analytical model. Conversely, when the two laser pulses differ from each other, the pair-creation probability depends not only on the time delay but, in general, also on the temporal order of the pulses.
Jansen, M. J. A., & Müller, C. (2017). Strong-field Breit–Wheeler pair production in two consecutive laser pulses with variable time delay. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 766, 71–76. https://doi.org/10.1016/j.physletb.2016.12.056