Multiple Absorption and Emission of Photons in Strong Laser Fields: The Electrodynamics-Based Path Through the Hartemann-Kerman’s Radiation Intensity Equation

From the well-known Hartemann-Kerman[1] (HK in short) equation we derived an expression with similarity to the Quantum Electrodynamics (QED) amplitude having a Dirac-Delta function’s argument that can be interpreted as the multiple absorption and emission of single photons from a mathematical mechanism that uses the expansion in Bessel’s functions. Although the HK equation is conceived in a scenario purely classical the fact that the it yields a kind of momentum conservation, it can be sustained under the hypothesis that quantization in a classical framework can be restored uniquely in the cases where the laser field is superintense. Therefore, classical electrodynamics can also explain among others phenomena nonlinear Compton scattering as first studied by Hartemann and Kerman.