Matters Arising: On physical nature of the optical deDroglie-Mackinnon wave packets. ARISING FROM Layton A. Hall and Ayman F. Abouraddy Nature Physics https://doi.org/10.1038/s41567-022-01876-6 (2023)

Hall and Abouraddy [1] have reported first experimental observation of optical de Broglie-Mackinnon wave packets, which is a seminal achievement in the study of so-called non-diffracting optical pulses. These wave packets propagate in free space without spreading with subluminal relativistic velocities, i.e., with speeds slower but close to the velocity of light in vacuum. The experiments in [1] became possible thanks to the application of quite a witty method. Unfortunately, the explanation of the physical nature of the wave packets and their graphical and mathematical descriptions in the theoretical part of [1] suffer from some ambiguities that need to be clarified.