@misc{9251761,
  abstract     = {{This Master’s thesis explores the reconstruction of photoelectron angular distributions using spherical harmonic decomposition with a view of characterize the polarization state of the ionizing light field. Photoelectron angular distributions describe the measured angular distribution of emitted electrons, which follows from the probability of detecting an electron at different angles. These distributions contain information about the polarization properties of the ionizing field.

Three different reconstruction approaches are investigated. Firstly, a direct fitting method is explored, where a coherent sum of spherical harmonics is directly fitted to the angular distribution. Secondly, a projective method is investigated, where the distribution is first projected onto an orthogonal basis of spherical harmonics before being fitted. Finally, a machine learning approach based on a convolutional neural network with a physics-informed decoder is considered. The performance of each method is examined by investigating the reconstruction performance for several angular distributions corresponding to different polarization states, decreasing signal intensities, and varying noise levels. Both additive white Gaussian noise and Poisson noise are used in order to evaluate the methods under experimental-like conditions.

The results show that all three methods are able to accurately reconstruct the parameters describing the polarization state for both high-intensity and moderate-noise distributions. The direct fitting method gives the highest accuracy for varying signal intensity, while the projective method is most robust against Poisson noise. The machine learning method achieves comparable reconstruction performance to the two other methods, and provides more consistent predictions for different distributions, whereas the numerical optimization-based methods show a stronger dependence on the specific polarization state. A limitation observed for all methods is the difficulty in accurately reconstructing polarization states where one of the spherical harmonic coefficients used to describe the angular distribution approach zero.

Overall, the findings give insight into the potentials and limitations of the different reconstruction methods and their performance under different conditions. Possible improvements of the current methods, as well as future applications to more complex systems, are also discussed.}},
  author       = {{Randsalu, Nora}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Characterizing Photoelectron Momentum Distributions: Comparing Spherical Harmonic Reconstruction Methods}},
  year         = {{2026}},
}