UC San Diego

The linear Breit-Wheeler process ($\gamma\gamma\longrightarrow e^{-} e^{+}$) is one of the fundamental processes of quantum electrodynamics with many important astrophysical applications. However, almost a century has passed since it was theoretically proposed in 1934, and there is still no experimental observation of the linear Breit-Wheeler process using real photons. To produce linear Breit-Wheeler pairs, the collision of dense and energetic photons is required due to the small cross section and high photon energy threshold of this process, which is challenging to be achieved in laboratory conditions. On the other hand, the rapid development of laser technology has allowed the state-of-the-art laser facilities to produce laser pulses with intensities above $10^{22}\Wcmsqd$. Such high-intensity, multi-PW, and multi-beam laser facilities open up brand new opportunities for the experimental realization of the linear Breit-Wheeler pair creation.

This dissertation presents two schemes for producing the linear Breit-Wheeler pairs using currently available laser pulses, with the assistance of numerical tools we developed.We show that utilizing collective plasma effects beneficial for the linear Breit-Wheeler pair creation, one can achieve pair yields that was previously thought to be unattainable at current laser intensities. Compared to the pair yields reported in previous studies, the pair yields in the systems we propose are approximately two to three orders of magnitudes larger. We further show that by interacting with the strong fields in the laser-plasma system, a large proportion of the produced positrons can be accelerated to form collimated energetic positron beams in hundreds-of-MeV to GeV level. Our studies not only propose possible schemes for the first experimental observation of the linear Breit-Wheeler process in laboratory, but have also emphasized the existence of the previously overlooked linear Breit-Wheeler process in high-intensity laser-plasma interaction systems. The self-organized formation of collimated positron beams may also serve as a potential mechanism for energetic positron source.