A time-dependent generalized Floquet calculation of the laser-induced lineshape in attosecond transient absorption spectra
Xu-Han 旭涵 Wang 王, Di Zhao, P. Li
Abstract We introduce a time-dependent generalized Floquet (TDGF) approach to calculate attosecond transient absorption spectra of helium atoms subjected to the combination of an attosecond extreme ultraviolet (XUV) pulse and a delayed few-cycle infrared (IR) laser pulse. This TDGF approach provides a Floquet understanding of the laser-induced change of resonant absorption lineshape. It is analytically demonstrated that the phase shift of the time-dependent dipole moment that results in the lineshape changes consists of two components, the adiabatic laser-induced phase (LIP) due to the IR-induced Stark shifts of adiabatic Floquet states and the non-adiabatic phase correction due to the non-adiabatic IR-induced coupling between adiabatic Floquet states. Comparisons of the spectral lineshape calculated based on the TDGF approach with the results obtained with the LIP model [ Phys. Rev. A 88 033409 (2013)] and the rotating-wave approximation (RWA) are presented for several typical cases, demonstrating that TDGF universally and accurately captures IR-induced lineshape changes. It is suggested that the LIP model works as long as the generalized adiabatic theorem [ PRX Quantum 2 030302 (2021)] holds, and the RWA works when the higher-order IR-coupling effect in the formation of adiabatic Floquet states is neglectable.
Chinese Physics B•Sep 17, 2025•2 citations