See Itzykson, C.; Zuber, J.-B. (1985). Quantum Field Theory. McGraw-Hill. pp. 73–74. ISBN0-07-032071-3. Eq. 2.87 is identical to eq. 2.86, except that it features j instead of l.
Varró, Sándor (2014). "A new class of exact solutions of the Klein–Gordon equation of a charged particle interacting with an electromagnetic plane wave in a medium". Laser Physics Letters. 11: 016001. arXiv:1306.0097. doi:10.1088/1612-2011/11/1/016001.
Varró, Sándor (2014). "A new class of exact solutions of the Klein–Gordon equation of a charged particle interacting with an electromagnetic plane wave in a medium". Laser Physics Letters. 11: 016001. arXiv:1306.0097. doi:10.1088/1612-2011/11/1/016001.