Organic molecular crystals (OMCs) are introduced as a novel target class for high-harmonic generation (HHG). In OMCs, neighboring molecules experience a weak van-der-Waals coupling, considerably smaller than covalent or ionic bonds in previous solid-state targets. However, this finite coupling leads to “solid like” features, e.g. a delocalization of electronic states over neighboring molecules. The perfect inherent alignment of all molecules makes OMCs an ideal target class for HH spectroscopy. With mid-IR pulses HHG from Pentacene crystals is demonstrated without imposing physical damage. For all harmonic orders it is found that the generation process is driven by collective intermolecular effects and not by the response of non-interacting aligned molecules. In contrast, in the more weakly coupled Tetracene, at least low order harmonic generation reflects also the symmetry of single molecular transitions.
Doctoral Seminar: Falk-Erik Wiechmann
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