Probing and controlling the dynamics in diatomic molecules with intense ultrashort laser and
XUV pulses
Uwe Thumm
Department of Physics, Kansas State University, Manhattan, KS 66506, USA
Swift ionization of diatomic molecules in short intense pulses of electromagnetic radiation generates
molecular ions that either dissociate immediately or remain in bound excited states. These excited
states can be represented based on adiabatic molecular potential surfaces that support the rovibrational nuclear motion in the molecular ion. Both, the dissociative and bound nuclear motion can be
destructively imaged (with a time resolution of a few femtoseconds) using a second, delayed, pulse, by
recording nuclear kinetic-energy-release (KER) spectra as a function of the time delay between the two
pulses. I will discuss various aspects of such pump-probe studies, starting with the dissociative
ionization of the simplest molecule, H2, and illustrate how the ro-vibrational dynamics in H2+ can be
controlled [1] and revealed in measurable delay-dependent KER spectra. In particular, I will show how
quantum-beat spectroscopy, i.e., the harmonic time-series analysis of delay-dependent KER spectra,
allows the reconstruction of (external-field-dressed!) molecular potential curves and holds promise for
the full reconstruction of vibrational nuclear wave packets (up to an overall phase) [2-4].
In the second part of this talk I will move on to heavier diatomic molecules, where ionization by an ultrashort pump pulse tends to populate several intermediate excited electronic states of the molecular ion.
By comparing characteristic features of simulated KER spectra (vibrational periods, wave packet revivals,
quantum beats, etc.) that result from the nuclear motion on individual adiabatic potential curves of the
molecular ion with measured KER spectra, we developed a scheme for identifying intermediate ionic
states that are relevant for the dissociation process. I will review numerical examples for this simulationaided interpretation of measured KER spectra for N2, O2, and CO molecules for pump-probe experiments
with both IR laser [4-6] and Free-Electron-Laser XUV pulses [7]. I plan to conclude with a brief discussion
of the dissociation dynamics of noble gas dimers in two-color infrared intense laser fields for which our
calculations predict a striking “delay gap” in the KER spectra. This gap originates in a frustrated
dissociation mechanism and was recently measured for Ar2 [8]. Comparing pump-probe-pulse-delay
dependent KER spectra for noble gas dimers of increasing mass, reveals increasingly prominent i) finestructure effects in and ii) classical aspects of the nuclear vibrational motion [9].
[1] T. Niederhausen, U. Thumm, and F. Martin, in, J. Phys. B: At. Mol. Opt. Phys. 45, 105602 (2012). [2] B.
Feuerstein, T. Ergler, A. Rudenko, K. Zrost, C.D. Schröder, R. Moshammer, J. Ullrich, T. Niederhausen, and U.
Thumm, Phys. Rev. Lett. 99, 153002 (2007). [3] U. Thumm, T. Niederhausen, and B. Feuerstein, Phys. Rev. A 77,
063401 (2008). [4] M. Magrakvelidze, A. Kramer, K. Bartschat, and U. Thumm, J. Phys. B: At. 47, 124003 (2014). [5]
S. De, M. Magrakvelidze, I. Bocharova, D. Ray, W. Cao, I. Znakovskaya, H. Li, Z. Wang, G. Laurent, U. Thumm, M. F.
Kling, I. V. Litvinyuk, I. Ben-Itzhak, and C. L. Cocke, Phys. Rev. A 84, 043410 (2011). [6] M. Magrakvelidze, C.M.
Aikens, and U. Thumm, Phys. Rev. A 86, 023402 (2012). [7] Magrakvelidze, O. Herrwerth, Y.H. Jiang, A. Rudenko,
M. Kurka, L. Foucar, K.U. Kühnel, M. Kübel, Nora G. Johnson, C.D. Schröter, S. Düsterer, R. Treusch, M. Lezius, C.L.
Cocke, I. Ben-Itzhak, R. Moshammer, J. Ullrich, M. F. Kling, and U. Thumm, Phys. Rev. A 86, 013415 (2012). [8] J.
Wu, M. Magrakvelidze, A. Vredenborg, L. Ph. H. Schmidt, T. Jahnke, A. Czasch, R. Dörner, and U. Thumm, Phys. Rev.
Lett. 110, 033004 (2013). [9] M. Magrakvelidze and U. Thumm, Phys. Rev. A 88, 013413 (2013).