Berlin 2001 – wissenschaftliches Programm

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A: Atomphysik

A 5: Posters Tuesday (Photoionisation, Multi Photon Processes)

A 5.33: Poster

Dienstag, 3. April 2001, 12:30–15:00, AT3

Collective Effects in Resonant Multiphoton Ionisation of Atomic Deuterium — •B J Shortt¹, F Giammanco², P J M van der Burgt¹, and R W O’Neill¹ — ¹Dept. of Experimental Physics, National University of Ireland, Maynooth, Ireland — ²Dipartimento di Fisica, Universita di Pisa, Pisa, Italy

A transient laser plasma is formed by 3-photon ionisation of deuterium with an excimer-pumped dye laser (pulsewidth 13 ns, wavelength 243 nm, maximum intensity 300 MW/cm2). Inside a vacuum chamber the laser beam is crossed with a deuterium beam produced by an RF discharge source. The photoionisation is resonant with the metastable 2s state. An extraction electric field accelerates the ions towards a detector, and quenches the metastable atoms. The emitted Lyman-alpha photons are also detected.

At high laser intensities collective effects due to the mutual interaction of the photo-electrons and the ions affect the time- evolution of the plasma. The resonant multiphoton ionisation is influenced by the Stark mixing of the 2s and 2p states in the collective field. Measurements of the ion and photon yields as a function of laser intensity and wavelength will be presented.