# Partial-wave analysis of multiphoton ionization of sodium by femtosecond laser pulses of 800 nm wavelength in over-the-barrier ionization regime

## TL;DR

This study performs a detailed partial-wave analysis of sodium multiphoton ionization by 800 nm femtosecond laser pulses, revealing how different ionization channels contribute to photoelectron spectra and how pulse parameters can control these contributions.

## Contribution

It introduces a numerical partial-wave analysis method for multiphoton ionization spectra, linking spectral peaks to specific ionization channels and symmetries, and suggests control over ionization pathways via pulse parameters.

## Key findings

- Spectra agree with experimental results.
- Different ionization channels contribute to spectral peaks.
- Pulse parameters can influence ionization channel contributions.

## Abstract

Multiphoton ionization of sodium by laser pulses of 800 nm wavelength and 57 fs duration is studied in the range of laser peak intensities belonging to over-the-barrier ionization regime. Photoelectron momentum distributions (PMD) and the energy spectra are determined numerically by solving the time dependent Schr\"odinger equation. The calculated spectra agree well with the spectra obtained experimentally by Hart et al. [Phys. Rev. A 93, 063426 (2016)]. The contributions of photoelectrons with different values of the orbital quantum number in the PMD are determined by expanding the photoelectron wave function in terms of partial waves. Partial wave analysis of the spectral peaks related to Freeman resonances has shown that each peak has photoelectron contributions from different ionization channels which are characterized by different photoelectron energies and different symmetries of released photoelectron wave-packets. These findings are justified by calculating the populations of excited states during the pulse. Our analysis indicates that the contribution of specific ionization channels in the total photoelectron yield might be selectively increased by varying to some extent the values of pulse parameters used here.