Non-local Quantum Electrodynamics. II. Possibility of correlated   2n-photon absorption in gases leading to VERY High frequency spontaneous   emission and Very high order Harmonic Generation
  In a recent work [Mod. Phys. Lett A13, p-1265 (1998)] we expounded a non-local Quantum Electrodynamics (QED) which predicted a linear two-photon absorption by an atom placed in a laser field of appropriate intensity and frequency. In this paper we extend our earlier work to show that the theory allows for linear 2n-photon absorption by gaseous matter where, under suitable conditions, n may literally run upto thousands. The consequences of this extension of the theory are outlined and predictions are made which may be verified in laboratories. 
Krishna Rai Dastidar and T. K. Rai Dastidar (India Association for the   Cultivation of Science)