  A comment on the paper by S. M. Mahajan and F. A. Asenjo "Interacting quantum
and classical waves: Resonant and non-resonant energy transfer to electrons
immersed in an intense electromagnetic wave" [Phys. Plasmas 29, 022107 (2022)]
where the authors use a model based on the Klein-Gordon equation to discuss
particle energization by a transverse electromagnetic wave in a plasma. It is
shown that the results of the paper are easily obtained in a classical
approach, so that no quantum effect has to be invoked. Moreover, some mistakes
and misinterpretations in the paper have been corrected. The (un)suitability of
the proposed mechanism to account for generation of extremely energetic
particles in both laboratory and astrophysical scenarios is also discussed.
