Photoemission spectroscopy is central to understanding the inner workings of condensed matter, from simple metals and semiconductors to complex materials such as Mott insulators and superconductors. Most state-of-the-art knowledge about such solids stems from spectroscopic investigations, and use of subfemtosecond light pulses can provide a time-domain perspective. For example, attosecond (10 seconds) metrology allows electron wave packet creation, transport and scattering to be followed on atomic length scales and on attosecond timescales. However, previous studies could not disclose the duration of these processes, because the arrival time of the photons was not known with attosecond precision. Here we show that this main source of ambiguity can be overcome by introducing the atomic chronoscope method, which references all measured timings to the moment of light-pulse arrival and therefore provides absolute timing of the processes under scrutiny. Our proof-of-principle experiment reveals that photoemission from the tungsten conduction band can proceed faster than previously anticipated. By contrast, the duration of electron emanation from core states is correctly described by semiclassical modelling. These findings highlight the necessity of treating the origin, initial excitation and transport of electrons in advanced modelling of the attosecond response of solids, and our absolute data provide a benchmark. Starting from a robustly characterized surface, we then extend attosecond spectroscopy towards isolating the emission properties of atomic adsorbates on surfaces and demonstrate that these act as photoemitters with instantaneous response. We also find that the tungsten core-electron timing remains unchanged by the adsorption of less than one monolayer of dielectric atoms, providing a starting point for the exploration of excitation and charge migration in technologically and biologically relevant adsorbate systems.
We present an optical parametric chirped pulse amplifier (OPCPA) delivering CEP-stable ultrashort pulses with 7 fs, high energies of more than 1.8 mJ and high average output power exceeding 10 W at a repetition rate of 6 kHz. The system is pumped by a picosecond regenerative thin-disk amplifier and exhibits an excellent long-term stability. In a proof-of-principle experiment, high harmonic generation is demonstrated in neon up to the 61 order.
Based on visible and mid-infrared transient absorption studies, probing the inter-and intraband dynamics, respectively, of magnesium phthalocyanine (MgPc) organic semiconductors, we were able to develop a model to describe the dynamics and the resulting optical response. We demonstrate how the model could offer insights into the dynamics of more complicated systems such as amorphous MgPc samples obtained by established preparation methods. In particular, we show a clear dimensionality difference of the exciton dissipation mechanism between crystalline and amorphous MgPc, which we resolve in the intraband dynamics, and how this result can also be deduced from the interband dynamics through the implementation of the developed model.
Non-covalent intermolecular hybridization in a 2D molecular self-assembly gives rise to a narrow electronic energy band, a promising prospect for organic nanoelectronics.
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