Darmstadt 2008 – wissenschaftliches Programm

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A: Fachverband Atomphysik

A 27: Posters: Electron scattering and recombination

A 27.6: Poster

Donnerstag, 13. März 2008, 16:30–18:30, Poster C3

A Photoemission Electron Source Based on GaAs Semiconductor Crystal Used in a Reaction Microscope — •Vladimir Borovik, Steffen Lüdemann, Toshiyasu Ichioka, Claus Dieter Schröter, Alexander Dorn, and Joachim Ullrich — Max-Planck Institute of Nuclear Physics, Saupfercheckweg 1, D-69117 Heidelberg, Germany

The dynamics of fundamental few-body quantum systems can be investigated by observing single and multiple ionization of atoms and molecules in the near-threshold region. We employ recoil-ion and electron momentum spectroscopy which allows us to measure the momentum vectors of several ions and electrons created in such reactions. For electron-impact ionization, the momentum resolution critically depends on the incident electron beam quality. For our experiments an electron source with a narrow energy distribution at small energies of the beam is required. Recent measurements were limited by the characteristics of the thermocathode electron source used (see, e.g., [1]). We have built a new pulsed photoemission electron source based on a GaAs semiconductor crystal activated to a state of negative electron affinity. Since the electron beam is produced by irradiating the crystal surface with a picosecond laser beam, its time structure is essentially defined by the characteristics of the laser. The current status of the photoelectron source and main technical issues related to its implementation in the collision experiments using the so-called reaction microscope [2] will be discussed. [1] M. Durr et al., Phys. Rev. Lett. 96, 243202 (2006). [2] J. Ullrich et al., Rep. Prog. Phys. 66, 1463 (2003).