299 / 2023-04-26 08:29:27

Superradiance and temporal coherence in plasma accelerators: New pathways towards FEL brightnesses in plasma

Coherent light sources, such as free electron lasers, provide bright beams for biology, chemistry, physics and advanced technological applications. As their brightness increases, these sources are also becoming progressively larger, with the longest being several km long (e.g. LCLS). Plasma accelerators, instead, are much more compact, and can play a key role in bringing these sources to smaller laboratories. Reaching this goal requires orders of magnitude increase on the brightness delivered by plasma accelerator based light sources. In turn, a radical enhancement of beam brightness in plasma accelerator light sources depends directly on the onset of temporal coherence and superradiance. 



Here, we propose a new radiation emission mechanism that may bring temporal coherence and superradiance to plasma accelerator based light sources. The mechanism is suitable for experimental demonstrations in current plasma accelerator laboratories. Instead of focusing on single particle motions, we investigate the radiation produced by an ensemble of light emitting particles exhibiting collective, matter-wave effects. Such collective motions, which can be as simple as a plasma wave, are pervasive in plasmas and plasma based accelerators. We find that the trajectory of the centroid of such collective perturbation (which we denote as a quasi-particle) determines key radiation aspects, such as temporal coherence, just as if it were a single particle undergoing a similar trajectory. We apply this concept to obtain superradiant emission using relativististic electron bunches [1], and in plasma accelerator based-light sources, in order to generate broadband and narrow bandwidth superradiant and temporally coherent radiation in the XUV/soft-xray region [2]. We demonstrate our findings with theory and particle-in-cell simulations complemented by the Radiation Diagnostic for Osiris (RaDiO) [3].