Volkov solution for an electron in the two wave fields
  It is considered the Dirac equation with two different four-potentials of the plane electromagnetic waves. We derive the equation for the wave function which is generalized form of the Volkov equation. We find the solutions of the Dirac equation for two orthogonal waves. We determine the modified Compton formula for the scattering of two photons on an electron. 
Miroslav Pardy