Enhancement of vacuum birefringence with pump laser of flying focus

Vacuum birefringence is one of the most fascinating properties of quantum electrodynamics. In laser-induced vacuum polarization signatures, the interaction length is usually limited by the pump laser's Rayleigh length and temporal length. Here, we show that a flying focus pump with focus velocity -c can overcome the short interaction length of the tightly focused pump laser, providing high intensity and long interaction length at the same time, which may lead to the experimental detection of vacuum birefringence.