Bonn 2025 – scientific programme

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MO: Fachverband Molekülphysik

MO 9: Poster – Novel Approaches

MO 9.2: Poster

Tuesday, March 11, 2025, 14:00–16:00, Tent

Optimized Velocity Map Imaging Spectrometer for Deep-UV Measurements — •Fabian Westmeier, Nicolas Ladda, Jochen Mikosch, Thomas Baumert, and Arne Senftleben — Institute of Physics and CINSaT, University of Kassel, 34132 Kassel, Germany

Velocity Map Imaging spectroscopy [1] is a powerful method for investigating photoionization processes, by projecting the photoelectron angular distribution onto a position-sensitive detector. We present a spectrometer that is used to study the dynamics of chiral molecules via time-resolved photoelectron circular dichroism [2] with deep-UV photons. Such experiments often experience a high level of background signals due to photoelectrons generated at the spectrometer electrodes from scattered photons. Here we present our successful approaches to reduce this background. We achieved the biggest improvement by using thin electrodes, which minimize the surface area exposed to scattered light. A large hole in the repeller plate combined with an additional high-voltage electrode underneath results in the photoelectrons emitted from the repeller plate being captured by the electrode above. Furthermore, we designed light baffles exhibiting high UV absorption [3], which confine the opening angle for scattered light. To minimize overall scattering, we used thin single-crystal calcium fluoride (CaF2) windows.

[1]: A. T. J. B. Eppink, D. H. Parker, Rev. Sci. Instrum. 68, 3477-3484 (1997)

[2]: C. Lux et al., Angew. Chem. Int. Ed. 51, 5001-5005 (2012)

[3]: O. J. Clarkin, Dissertation, Queen's University, Canada (2012)

Keywords: Velocity Map Imaging; Background Signal Reduction; UV Light