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arXiv · 2505.14390

Comparison between Jacobi-Anger and saddle point methods to treat Above-threshold ionization

Danish Furekh Dar·Stephan Fritzsche
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Abstract

We present a detailed comparison of theoretical approaches for modeling strong-field ionization by few-cycle laser pulses. The dipole approximation is shown to accurately capture interference structures in photoelectron spectra, while non-dipole effects introduce significant momentum shifts along the propagation direction. Two complementary analytical methods are used: the Jacobi-Anger expansion provides complete spectral decomposition of transition amplitudes, whereas the saddle-point method efficiently identifies dominant ionization pathways. Through this comparative study within the strong-field approximation framework, we establish validity conditions and practical advantages for each approach. Our results provide guidelines for selecting theoretical methods for advancing the interpretation of strong-field processes. These findings provide a roadmap for interpreting strong-field ionization spectra and momentum distributions, highlighting where non-dipole effects and method choice critically alter predictions.

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Danish Furekh Dar, Stephan Fritzsche. 2025-05-20. Comparison between Jacobi-Anger and saddle point methods to treat Above-threshold ionization. https://doi.org/10.1088/1361-6455%2Fae187b

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