Regensburg 2025 – scientific programme

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O: Fachverband Oberflächenphysik

O 11: Electronic Structure of Surfaces: Spectroscopy, Surface States I

O 11.1: Talk

Monday, March 17, 2025, 15:00–15:15, H4

Optimizing the photon detection in inverse photoemission — •Jan Willermann, Fabian Schöttke, and Markus Donath — Physikalisches Institut, Universität Münster, Münster, Germany

The detection of vacuum-ultraviolet photons (ℏ ω = 9.9 eV) in inverse-photoemission experiments is usually carried out with gas-filled counting tubes. Commonly, iodine/argon gas fillings were used for Geiger-Müller type photon detection. Recently, the gas filling was replaced by acetone to increase stability and the operation was changed to proportional mode [1]. While doing this, the counting tube geometry must not necessarily be changed. We carried out systematic measurements to understand the photon detection process in acetone-filled counting tubes and optimize the geometry accordingly. In the range of optimal gas pressures, we found that the photon mean free path in acetone is in scale of a few millimeters instead of a few centimeters as in iodine/argon. Furthermore, we observed that the electron mean free path in proportional-type counting tubes is also reduced to few millimeters. In comparison, the mean free path of electrons in Geiger-Müller-type counting tubes is in the range of the radius of the counting tube. As a consequence, the position of the cathode wire close to the entrance window becomes a critical parameter for the detection efficiency.

[1] C. Thiede et al., Meas. Sci. Technol. 29, 065901 (2018).

Keywords: inverse photoemission; photon detection