We pursue development of new laser sources/technology, –some based in part on femtosecond frequency combs– and then employ of them in innovative and new spectroscopic studies on condensed matter systems. We have demonstrated a high repetition rate (>50 MHz) femtosecond source with photon energies reaching 40 eV and energy resolutions of 25 meV suitable for time-resolved photoemission spectroscopy. Current laser work is focussed on scaling to lower repetition rates (1-10 MHz) and expanding spectral coverage of a synchronized pump source to the mid infrared.

Working with Andrea Damascelli’s group, we are employing our XUV frequency comb source and accompanying laser-based ultrafast sources for time-resolved, angle resolved photoemission spectroscopy (tr-ARPES) of condensed matter systems exhibiting correlated electron behavoir and other quantum effects. At present, the choices for high photon energy sources for lab-based studies of ARPES and tr-APRES are non-ideal: XUV lamps with their fixed photon energies or laser-based sources with low (< 6 eV) photon energies. Through development and optimization of our XUV frequency comb source ultrafast source we have fulfilled a hitherto missing lab-based tool enabling us to study the time dynamics of electronic excitations of solids over a portion of momentum space larger than the first Brillouin zone. More specifically, the additional capability from the ultrafast time resolution will allow disentangling the elementary excitations responsible for strongly-correlated electron behavior using a source located within our laboratories.

In a second thrust and in collaboration with Prof. Sarah Burke’s laboratory we have very recently begun a research effort on improving the charge transfer (and hence efficiency) of organic photovoltaics (PV) by studying the coupled spatial-temporal dynamics of PV interfaces at the molecular level. Employing scanning probe microscopy (SPM) in tandem with time-resolved, angle-resolve photoemission spectroscopy (tr-ARPES) we seek to optimize PV’s conversion efficiencies by tracking (at the nanoscale) electronic and vibrational coupling in metal organic PV molecules and maximizing charge transfer at surface interfaces. Through these efforts we seek to record (simultaneously in both in the spatial and temporal domains) reaction pathways and associated quantum coherences through vibrational and electronic states following photoexcitation with goals of uncovering the mechanisms (and thus improving) energy transport in PVs.

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