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Following positive laboratory-scale experiments, we investigated the ability to trigger real-scale lightning using ionized filaments generated by ultrashort laser pulses in the atmosphere. Under thunderstorm conditions, we observed electric events synchronized with the laser pulses.

We report the first observation of the high vibronic levels of the ${\mathrm{Na}}_{3}$ ground state, performed by stimulated emission spectroscopy. The highest cross sections of the process, which uses the ${C}^{2}$E'' state as an intermediate state, are obtained for combinations of symmetric stretch and bending modes. These experimental results are of primary importance for the understanding of energy-level structures in systems exhibiting strong vibronic coupling.

Die Methode der 2-Photonen-Ionisierung wurde erfolgreich an Alkali-Aggregaten zur massenselektiven optischen Spektroskopie eingesetzt. Die dabei erzielte Nachweiswahrscheinlichkeit ist konventionellen Ionisierungsmethoden weit uberlegen. Die Spektren ermoglichen Aussagen uber Geometrie und Temperatur der untersuchten Partikel. Die Methode erscheint daher sehr geeignet, zerstaubte Neutralteilchen zu analysieren.

Inner-shell autoionization spectra obtained with synchrotron radiation are reported for mercury clusters ${\mathrm{Hg}}_{n}$, $n\ensuremath{\le}40$. For the small clusters $n\ensuremath{\le}12$ the spectral behavior as a function of size is interpreted in terms of an excitonic model. For larger cluster sizes a gradual deviation from van der Waals bonding is observed. The asymmetry occuring in the line profiles reflects the progressive construction of the $\mathrm{sp}$ conduction band.