A new theoretical approach to high order harmonic generation

Summary form only given. A mechanism underlying high order harmonic generation (HHG) is presented here. The theoretical predictions compared with experimental results are also discussed. Drawing from the nonperturbative QED scattering theory formalism recently developed for multiphoton ionization (MPI) and above threshold ionization (ATI), the transition matrix describing the interactions of an atom with a quantized optical field through quantum Volkov states is derived. The expression includes the transition from the intermediate Volkov states, and while our derivation maintains conservation of momentum and energy of electron-photon system, it gives out harmonic generation features