Laser-induced synchrotron self-absorption probed with detailed simulations

Electrons on the surface of a plasma can be irradiated so strongly that they emit gamma rays as synchrotron radiation, like the process in some strongly magnetized astrophysical environments. Such magnetized and dense regions are a major area of study in plasma physics, and scientists are actively working to better understand the interactions of energetic electrons and photons in those areas.

Simulations of the photon emission and electron-positron pair creation have been conducted for an irradiated plasma, but not for the corresponding absorption process. For the first time, Blackburn et al. simulate photons absorbed by the relativistic electrons that emitted them — what is known as synchrotron self-absorption in astrophysics.

This process is commonly observed in space, from supernovae to gamma-ray burst afterglows to black hole X-ray binary systems and could soon be seen in upcoming high-powered laser facilities. In typical environments, the subsequent gamma ray absorption is much weaker than the emission. But in dense environments, the gamma rays can be scattered or reemitted, instead of just being absorbed. The simulations help show the details of such interactions, which occur on femtosecond timescales.

The authors used particle-in-cell simulations to study the gamma rays’ interactions in dense environments, including interplays between the quantum electrodynamics process of spontaneous photon emission, and the particle-particle processes of absorption and stimulated emission. The authors consider the work a first step using an ideal situation.

“The situation in a real experiment is much more complex, and that’s something that still needs to be investigated,” said author Tom Blackburn.

Source: “Self-absorption of synchrotron radiation in a laser-irradiated plasma,” by T. G. Blackburn, A. J. MacLeod, A. Ilderton, B. King, S. Tang, and M. Marklund, Physics of Plasmas (2021). The article can be accessed at https://doi.org/10.1063/5.0044766 .