Zhang, X., Li, L., Zhu, X. H., Liu, K., Liu, X., Wang, D., Lan, P., Barth, I., Lu, P.
Subpetahertz helicity-modulated high-order harmonic radiation
Physical Review A 98, (2),pp 023418/1-9 (2018)
We demonstrate a scheme to produce coherent extreme ultraviolet and soft x-ray radiation with subpetahertz
temporal helicity modulation, based on the high harmonic generation from current-carrying orbitals driven by
intense linearly polarized laser fields. It is found that the electronic angular momentum of the orbitals oscillates
periodically in femtosecond scale in the driving field. This so-far undescribed phenomenon is qualitatively
interpreted and attributed to the laser-induced energy shift of orbitals. Consequently, the polarization of the
harmonic radiation switches periodically in the temporal domain between left and right elliptical polarizations,
and the frequency of the helicity modulation reaches subpetahertz. By varying the intensity of the laser field, the
modulation frequency can be continuously controlled. This light source will serve as a potential tool to detect
and manipulate the ultrafast dynamics in magnetic materials and chiral media.
TH-2018-30