Addendum: Mapping electron dynamics in highly transient EUV photon-induced plasmas: a novel diagnostic approach using multi-mode microwave cavity resonance spectroscopy (2018 J PHYS D APPL PHYS 52 034004)

A new approach for an in-line beam monitor for ionizing radiation was introduced in a recent publication (Beckers, J., et al. "Mapping electron dynamics in highly transient EUV photon-induced plasmas: a novel diagnostic approach using multi-mode microwave cavity resonance spectroscopy." Journal of Physics D: Applied Physics 52.3 (2018): 034004.). Due to the recent detection and investigation of an additional third decay regime of the afterglow of an extreme ultraviolet photon-induced plasma described in a later article (Platier, B., et al. "Transition of ambipolar-to-free diffusion in the decay of an extreme ultraviolet photon-induced low-pressure argon plasma." Applied Physics Letters 116.10 (2020), 103703.) there is an additional reason for a minimum number of photons for this approach to work. Near or below this threshold, we explain that the response time of the diagnostic method is a limiting factor. Further, a second limit for the number of photons within a pulse is formalized related to the trapping of highly energetic free electrons.