An electron of helium atom under a high-intensity laser field
  We scrutinize the behavior of eigenvalues of an electron of Helium atom as it interacts with electric field directed along $z$-axis and exposed to linearly polarized intense laser field radiation. In order to achieve this, we freeze one electron of the helium atom at its ionic ground state and the motion of the second electron in the ion core is treated via a more general case of screened Coulomb potential model. Using the Kramers-Henneberger (KH) unitary transformation, which is semiclassical counterpart of the Block-Nordsieck transformation in the quantized field formalism, the squared vector potential that appears in the equation of motion is eliminated and the resultant equation is expressed in KH frame. Within this frame, the resulting potential and the corresponding wave function have been expanded in Fourier series and using Ehlotzkys approximation, we obtain a laser-dressed potential to simulate intense laser field. By fitting the more general case of screened Coulomb potential model into the laser-dressed potential, and then expanding it in Taylor series up to $\mathcal{O}(r^4,\alpha_0^9)$, we obtain the solution (eigenvalues and wave function) of an electron of Helium atom under the influence of external electric field and high-intensity laser field, within the framework of perturbation theory formalism. We found that the variation in frequency of laser radiation has no effect on the eigenvalues of an electron of helium for a particular electric field intensity directed along $z$-axis. Also, for a very strong external electric field and an infinitesimal screening parameter, the system is strongly bound. This work has potential application in the areas of atomic and molecular processes in external fields including interactions with strong fields and short pulses. 
Babatunde James Falaye, Guo-Hua Sun, Adenike Grace Adepoju, Muhammed   S. Liman, K. J. Oyewumi and Shi-Hai Dong
physics.atom-ph physics.plasm-ph quant-ph