Exact Keldysh theory of strong-field ionization: Residue method versus saddle-point approximation

  title={Exact Keldysh theory of strong-field ionization: Residue method versus saddle-point approximation},
  author={Yulian V. Vanne and Alejandro Saenz},
  journal={Physical Review A},
In recent articles [K. Mishima et al., Phys. Rev. A, 66, 033401 (2002); S. D. Chao, Phys. Rev. A, 72, 053414 (2005)] it was proposed to use the residue theorem for the exact calculation of the transition amplitude describing strong-field ionization of atomic systems within Keldysh theory. This should avoid the necessity of applying the method of steepest descent (saddle-point approximation). Comparing the results of both approaches for atomic hydrogen a difference by a factor of 2 was found for… 
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