(a) Typical pump-probe scheme, here in germanium as example. A VIS-NIR pulse photoexcites the semiconductor, initiating valence to conduction band transitions. A time-delayed broadband XUV pulse probes the transient state of the material by promoting a core-level electron to unoccupied states. (b) Broadband attosecond pulse spectra are shown that can be produced across a wide spectral range, giving core-level access to dynamics in various materials. The energy separations allow probing different atomic species separately in semiconductor compounds. (c) Time-resolved XUV absorption spectroscopy allows measuring carrier populations, electronic effects such as Coulomb screening, lattice expansions (phonons) as well as many-body effects (e.g. carrier-carrier scattering), that each result in distinct spectroscopic signatures around the chosen absorption edge (exemplary differential XUV absorbances in germanium are indicated).
S. K. Cushing, M. Zürch, P. M. Kraus, L. M. Carneiro, A. Lee, H.-T. Chang, C. J. Kaplan, S. R. Leone. Hot phonon and carrier relaxation in Si(100) determined by transient extreme ultraviolet spectroscopy, Structural Dynamics 5, 054302 (2018).
C. J. Kaplan, P. M. Kraus, A. D. Ross, M. Zürch, S. K. Cushing, M. F. Jager, H.-T. Chang, E. M. Gullikson, D. M. Neumark, S. R. Leone. Femtosecond Tracking of Carrier Relaxation in Germanium with Extreme Ultraviolet Transient Reflectivity, Physical Review B 97, 205202 (2018).
P. M. Kraus, M. Zürch, S. K. Cushing, D. M. Neumark, S. R. Leone. The Ultrafast X-ray Spectrocopic Revolution in Chemical Dynamics, Nature Reviews Chemistry 2, 82-94 (2018).
M. Zürch, H.-T. Chang, P. M. Kraus, S. K. Cushing, L. J. Borja, A. Gandman, J. S. Prell, D. Prendergast, C. D. Premmaraju, D. M. Neumark, and S. R. Leone. Carrier Thermalization and Trapping in Silicon-Germanium Alloy Probed by Attosecond XUV Transient Absorption Spectroscopy, Structural Dynamics 4 (4), 044029 (2017).
M. Zürch, H.-T. Chang, L. J. Borja, P. M. Kraus, S. Cushing, A. Gandman, C. J. Kaplan, M. H. Oh, J. S. Prell, D. Prendergast, C. D. Premmaraju, D. M. Neumark, and S. R. Leone. Direct and Simultaneous Observation of Ultrafast Electron and Hole Dynamics in Germanium, Nature Communications 8:15734, 1-11 (2017).