Signatures of transient electron localisation in high-order harmonic generation

ABSTRACT

We identify and explain signatures of ongoing single-electron nonadiabatic dynamics in the high-order harmonic generation (HHG) spectrum of H⁺ ₂. We establish the necessary laser parameter criteria for the modulation of the highest energy section of the HHG spectrum by suppressed ionisation due to transient electron localisation. This minimum is also shown to enable the emergence of an unusually complex interference structure at the highest energies of the spectrum caused by the breaking of inversion symmetry during sequential recombination events of the electron wavepacket. By inspecting the time-domain structure of the emitted radiation, we identify the role of transient electron localisation in modulating the amplitudes of individual peaks within the attosecond pulse train. Finally, an analysis of the phase mismatch accumulated within this highly structured region of HHG is performed, showing qualitative differences in coherence lengths present in different regions of the spectrum.

Keywords:

• High-order harmonic generation
• strong-field effects
• nonadiabatic electron dynamics

Acknowledgments

The authors acknowledge Carlos Hernandez-Garcia for discussions.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

M. R. Miller was supported by the National Science Foundation Graduate Research Fellowship [grant number DGE 1144083], the US Department of Energy Office of Basic Energy Science, Chemical Sciences, Geosciences and Biosciences Division, Atomic, Molecular and Optical Sciences Program [award number DE-FG02-09ER16103] and the US National Science Foundation [grant number PHY-1125844]. A. Jaroń-Becker was supported by the US National Science Foundation [grant number PHY-1125844] and the Air Force Office of Scientific Research [award number FA9550-16-1-0121]. A. Becker was supported by the US Department of Energy Office of Basic Energy Science, Chemical Sciences, Geosciences and Biosciences Division, Atomic, Molecular and Optical Sciences Program [award number DE-FG02-09ER16103] . This work utilised the Janus supercomputer, which is supported by the US National Science Foundation grant number CNS-0821794 and operated by the University of Colorado Boulder.