Mollow Sidebands

We have shown that sidebands of the usual odd harmonics occur in high harmonic spectra of open shell molecules at equilibrium geometries. The sidebands are due to a driving laser induced one-photon coupling (Rabi flopping) between one of the inner valence orbitals and the HOMO, a mechanism analogous to Mollow triplets known from quantum optics. The phenomenon is found and illustrated for parallel as well as perpendicular transitions, di-, tri- and polyatomic molecules (see Figure).

Y. Xia and A. Jaron-Becker, Opt. Express 24, 4689 (2016)

Multielectron Contributions in HHG

High harmonic generation (HHG) is an important spectroscopic tool to study the response of molecules to intense laser fields. Usually, in these studies the single-active-electron approximation is applied, in which the dynamics of electrons from different orbitals are considered independently from each other. However, using time-dependent density functional theory we have shown that multielectron effects play an important role for the interpretation of recent experimental data for the ellipticity of higher-order harmonics from nitrogen molecules. In particular, our results contain essential contributions from the HOMO, the HOMO-1 and the HOMO-2 orbitals over the whole HHG spectrum (see Figure).

Y. Xia and A. Jaron-Becker, Opt. Lett. 39, 1463 (2014)