Publications

2025

1. 

   Photoionization dynamics in intense few-cycle twisted laser pulses

   Danish Furekh Dar, Anne Weber, Shreyas Ramakrishna, and Stephan Fritzsche

   Phys. Rev. A, May 2025

   DOI

2. 

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

   Danish Furekh Dar and Stephan Fritzsche

   Journal of Physics B: Atomic, Molecular and Optical Physics, Nov 2025

   Abs DOI

   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.

2024

1. 

   Nonlinear interference and electron dynamics: Probing photoelectron momentum distributions in strong-field ionization

   Danish Furekh Dar and Stephan Fritzsche

   Phys. Rev. A, Apr 2024

   DOI

2023

1. 

   Nondipole strong-field approximation for above-threshold ionization in a few-cycle pulse

   Danish Furekh Dar, Björn Minneker, and Stephan Fritzsche

   Phys. Rev. A, May 2023

   DOI
2. Pulse Cycle Dependent Nondipole Effects in Above-Threshold Ionization

   Danish Furekh Dar and Stephan Fritzsche

   Atoms, May 2023

   Abs DOI

   In this study, we employ strong field approximation (SFA) to investigate the influence of the number of pulse cycles on above-threshold ionization within the framework of nondipole theory. The SFA enables the analysis of the ionization process under the dominance of the electric field, compared to other factors such as the binding potential of an atom. Nondipole effects, including higher-order multipole fields, can significantly impact ionization dynamics. However, the interaction between nondipole effects and pulse cycles remains unclear. Therefore, we investigate the pulse cycle dependence of ionization and examine peak shifts in Kr and Ar atoms. Our findings have implications for comprehensively understanding the effects of electromagnetic fields on electron behavior. The insights gained from this study provide valuable guidance for future research in strong field ionization.

2021

1. Radiative transition properties of singly charged magnesium, calcium, strontium and barium ions

   Mandeep Kaur, Danish Furekh Dar, B.K. Sahoo, and Bindiya Arora

   Atomic Data and Nuclear Data Tables, May 2021

   Abs DOI

   Accurate values of electric dipole (E1) amplitudes along with their uncertainties for a number of transitions among low-lying states of Mg+, Ca+, Sr+, and Ba+ are listed by carrying out calculations using a relativistic all-order many-body method. By combining experimental wavelengths with these amplitudes, we quote transition probabilities, oscillator strengths and lifetimes of many short-lived excited states of the above ions. The uncertainties in these radiative properties are also quoted. We also give electric quadrupole (E2) and magnetic dipole (M1) amplitudes of the metastable states of the Ca+, Sr+, and Ba+ ions by performing similar calculations. Using these calculated E1, E2 and M1 matrix elements, we have estimated the transition probabilities, oscillator strengths and lifetimes of a number of allowed and metastable states. These quantities are further compared with the values available from the other theoretical studies and experimental data in the literature. The present data will be useful for the astrophysical observations, laboratory analysis and simulations of spectral properties in the above considered alkaline-earth metal ions.