Leveraging similarity in laser–microchannel interaction from high to ultra-high intensity*

Similarity arguments and scaling relations are frequently-sought tools for the design of future ultra-relativistic laser-plasma experiments. While certain phenomena, such as non-perturbative quantum electrodynamics, are only accessible at ultra-high intensity, other aspects of ultra-relativistic laser-plasma interaction can be reproduced at lower intensity. In the context of relativistically transparent laser-microchannel interaction, we demonstrate that an appropriate scaling of spatial and temporal parameters produces qualitatively similar behavior between high and ultra-high intensity. This result enables past, modestly-relativistic experiments to inform future experimental design. In particular, similarity arguments motivate the exploration of the ultra-intense long-pulse regime, in which ion motion plays an important and often beneficial role in the production of energetic electrons and photons.