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AKBP: Arbeitskreis Beschleunigerphysik

AKBP 2: Electron Sources and Cathodes

AKBP 2.4: Talk

Monday, March 18, 2024, 12:30–12:45, E 020

Quantum efficiency scan setup for the activation chamber of Photo-CATCH* — •Julian Schulze, Joachim Enders, Markus Engart, Maximilian Herbert, Maximilian Meier, and Victor Winter — Institut für Kernphysik, Fachbereich Physik, Technische Universität Darmstadt, Darmstadt, Germany

GaAs photocathodes are used to generate spin-polarized electron beams for a variety of applications. The quantum efficiency (QE) of a photocathode is defined as the ratio of extracted electrons to incident photons. GaAs cathodes are activated to negative electron affinity (NEA) by applying a thin layer of an alkali metal (esp. Cs) and an oxidant (eg. O2). The activation layer may be inhomogeneous and/or deteriorate during operation due to interaction with residual-gas atoms or ion back-bombardment. The QE thus is position-dependent. A map of the QE can be measured by raster scanning the cathode surface with a laser to find the region with maximum QE which is best suited for beam extraction. A QE scan setup based on a piezoelectric mirror mount and a position sensitive feedback detector has been designed and installed. This contribution presents the design and characterization of the QE scan setup as well as results of the first performed QE scans at the activation chamber of Photo-CATCH.

*Work supported by DFG (GRK 2128 AccelencE, project number 264883531)

Keywords: GaAs; Photocathodes; Electron Source; Quantum efficiency scan