https://doi.org/10.1140/epjb/e2016-70064-0
Regular Article
Tailored pump-probe transient spectroscopy with time-dependent density-functional theory: controlling absorption spectra
1 Nano-Bio Spectroscopy Group and ETSF, Universidad del País Vasco, CFM CSIC-UPV/EHU, 20018 San Sebastián, Spain
2 ARAID Foundation – Institute for Biocomputation and Physics of Complex Systems, University of Zaragoza Mariano Esquillor Gómez s/n, 50018 Zaragoza, Spain
3 Max Planck Institute for the Structure and Dynamics of Matter and Center for Free-Electron Laser Science, Luruper Chaussee 149, 22761 Hamburg, Germany
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e-mail: umberto.degiovannini@ehu.es
Received: 28 January 2016
Received in final form: 31 March 2016
Published online: 18 May 2016
Recent advances in laser technology allow us to follow electronic motion at its natural time-scale with ultra-fast time resolution, leading the way towards attosecond physics experiments of extreme precision. In this work, we assess the use of tailored pumps in order to enhance (or reduce) some given features of the probe absorption (for example, absorption in the visible range of otherwise transparent samples). This type of manipulation of the system response could be helpful for its full characterization, since it would allow us to visualize transitions that are dark when using unshaped pulses. In order to investigate these possibilities, we perform first a theoretical analysis of the non-equilibrium response function in this context, aided by one simple numerical model of the hydrogen atom. Then, we proceed to investigate the feasibility of using time-dependent density-functional theory as a means to implement, theoretically, this absorption-optimization idea, for more complex atoms or molecules. We conclude that the proposed idea could in principle be brought to the laboratory: tailored pump pulses can excite systems into light-absorbing states. However, we also highlight the severe numerical and theoretical difficulties posed by the problem: large-scale non-equilibrium quantum dynamics are cumbersome, even with TDDFT, and the shortcomings of state-of-the-art TDDFT functionals may still be serious for these out-of-equilibrium situations.
Key words: Computational Methods
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2016