Comment on: 'Interacting quantum and classical waves: Resonant and non-resonant energy transfer to electrons immersed in an intense electromagnetic wave' [Phys. Plasmas 29, 022107 (2022)]

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.
Comment: 2 pages. 2nd version reports an extended discussion and criticism