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.
Platier, B., van de Wetering, F. M. J. H., van Ninhuijs, M., Brussaard, G. J. H. S., Banine, V. Y., Luiten, O. J. J., & Beckers, J. (Accepted/In press). 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). Journal of Physics D: Applied Physics. https://doi.org/10.1088/1361-6463/ab8f53