Exact Keldysh theory of strongfield ionization: Residue method versus saddlepoint approximation
Abstract
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 strongfield ionization of atomic systems within Keldysh theory. This should avoid the necessity of applying the method of steepest descent (saddlepoint approximation). Comparing the results of both approaches for atomic hydrogen a difference by a factor of 2 was found for the 1s and an even more drastic deviation for the 2s state. Thus it was concluded that the use of the saddlepoint approximation is problematic. In this work the deviations are explained and it is shown that the previous conclusion is based on an unjustified neglect of an important contribution occurring in the application of the residue theorem. Furthermore, the applicability of the method of steepest descent for the ionization of Rydberg states is discussed and an improvement of the standard result is suggested that successfully removes the otherwise drastic failure for large principal quantum numbers.
 Authors:
 AG Moderne Optik, Institut fuer Physik, HumboldtUniversitaet zu Berlin, Hausvogteiplatz 57, D10117 Berlin (Germany)
 Publication Date:
 OSTI Identifier:
 20982351
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Physical Review. A; Journal Volume: 75; Journal Issue: 3; Other Information: DOI: 10.1103/PhysRevA.75.033403; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 74 ATOMIC AND MOLECULAR PHYSICS; APPROXIMATIONS; ATOMS; FAILURES; HYDROGEN; PHOTOIONIZATION; PHOTONATOM COLLISIONS; QUANTUM NUMBERS; RESIDUES; RYDBERG STATES; SADDLEPOINT METHOD; TRANSITION AMPLITUDES
Citation Formats
Vanne, Yulian V., and Saenz, Alejandro. Exact Keldysh theory of strongfield ionization: Residue method versus saddlepoint approximation. United States: N. p., 2007.
Web. doi:10.1103/PHYSREVA.75.033403.
Vanne, Yulian V., & Saenz, Alejandro. Exact Keldysh theory of strongfield ionization: Residue method versus saddlepoint approximation. United States. doi:10.1103/PHYSREVA.75.033403.
Vanne, Yulian V., and Saenz, Alejandro. Thu .
"Exact Keldysh theory of strongfield ionization: Residue method versus saddlepoint approximation". United States.
doi:10.1103/PHYSREVA.75.033403.
@article{osti_20982351,
title = {Exact Keldysh theory of strongfield ionization: Residue method versus saddlepoint approximation},
author = {Vanne, Yulian V. and Saenz, Alejandro},
abstractNote = {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 strongfield ionization of atomic systems within Keldysh theory. This should avoid the necessity of applying the method of steepest descent (saddlepoint approximation). Comparing the results of both approaches for atomic hydrogen a difference by a factor of 2 was found for the 1s and an even more drastic deviation for the 2s state. Thus it was concluded that the use of the saddlepoint approximation is problematic. In this work the deviations are explained and it is shown that the previous conclusion is based on an unjustified neglect of an important contribution occurring in the application of the residue theorem. Furthermore, the applicability of the method of steepest descent for the ionization of Rydberg states is discussed and an improvement of the standard result is suggested that successfully removes the otherwise drastic failure for large principal quantum numbers.},
doi = {10.1103/PHYSREVA.75.033403},
journal = {Physical Review. A},
number = 3,
volume = 75,
place = {United States},
year = {Thu Mar 15 00:00:00 EDT 2007},
month = {Thu Mar 15 00:00:00 EDT 2007}
}

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