Spatiotemporal structure of hard x-rays in particle-in-cell codes

The spatiotemporal structure of x-rays is important in a range of scenarios, from astrophysics, where it provides unique insights on the origin of energetic radiation in extreme conditions, to microscopy, where it can be important to design light sources to probe new properties of matter. Strong radiation bursts are usually associated with the motion of many individual electrons, where collective plasma effects can be important. The radiation emission from these processes are challenging to model analytically. Thus, numerical approaches are routinely used to describe radiation emission in plasmas. Typical radiation emission diagnostics can capture spectral properties of the emitted light. Instead, in this work, we describe a new radiation diagnostic that captures the spatiotemporal properties of radiation. The algorithm is ideal to describe the radiation from many particles and has been fully integrated with the particle-in-cell code OSIRIS. It has built-in spatial and temporal coherence effects, and can be readily applied to any radiation emission configuration where quantum effects can be neglected. We show that this new tool recovers the theoretical spectra of radiation emission and we use it to compute the spatiotemporal profile of betatron radiation in plasma accelerators.