We present a set-up for time-resolved X-ray diffraction based on a short pulse, laser-driven plasma X-ray source. The employed modular design provides high flexibility to adapt the set-up to the specific requirements (e.g. X-ray optics, sample environment) of particular applications. The configuration discussed here has been optimized towards high angular/momentum resolution and uses K α -radiation (4.51 keV) from a Ti wire-target in combination with a toroidally bent crystal for collection, monochromatization and focusing of the emitted radiation. 2 × 10 5 Ti-K α1 photons per pulse with 10 −4 relative bandwidth are delivered to the sample at 10 Hz repetition rate. This allows for high dynamic range (10 4 ) measurements of transient changes of the rocking curves of materials as for example induced by laser-triggered strain waves. PACS numbers: 78.47.J-, 61.05.C, 63.30.dd a) Klaus.Sokolowski-Tinten@uni-due.de

The operation of quantum dots (QDs) at highest possible temperatures is desirable for many applications. Capacitance-voltage spectroscopy (C(V )-spectroscopy) measurements are an established instrument to analyse the electronic structure and energy levels of self-assembled QDs. We perform C(V ) in the dark and C(V ) under the influence of non-resonant illumination, probing exciton states up to + X 4 on InAs QDs embedded in a GaAs matrix for temperatures ranging from 2.5 to 120 K. While a small shift in the charging spectra resonance is observed for the two spin degenerate electron s-state charging voltages with increasing temperature, a huge shift is visible for the electron-hole excitonic states resonance voltages. The s 2 -peak moves to slightly higher, the s 1 -peak to slightly lower charging voltages. In contrast, the excitonic states are surprisingly charged at much lower voltages upon increasing temperature. We derive a rate-model allowing to attribute and value different contributions to these shifts. Resonant tunnelling, state degeneracy and hole generation rate in combination with the Fermi distribution function turn out to be of great importance for the observed effects. The differences in the shifting behaviour is connected to different equilibria schemes for the peaks-s-peaks arise when tunnelling-in-and out-rates become equal, while excitonic peaks occur, when electron tunnelling-in-and hole-generation rates are balanced.

The transient acoustic response of a free-standing, polycrystalline thin Au film upon femtosecond optical excitation has been studied by time-resolved Debye-Scherrer X-ray diffraction using ultrashort Cu K α X-ray pulses from a laser-driven plasma X-ray source.The temporal strain evolution has been determined from the transient shifts of multiple Bragg diffraction peaks. The experimental data are in good agreement with the results of calculations based on the two-temperature model and an acoustic model assuming uni-axial strain propagation in the laser-excited thin film.

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