Molecular photoelectron spectrum in ultrashort laser fields: Autler-Townes splitting under rotational and aligned effects

Abstract

The molecular dynamics of Autler-Townes (AT) splitting in a multiphoton resonance ionization spectrum is numerically simulated using the time-dependent wave packet method for a rotating ${\mathrm{Na}}_{2}$ molecule with a linearly polarized laser pulse. Employing the Fourier grid method and Legendre polynomials as basis functions, the initial wave packet is directly propagated using the split operator method. Wave packet dynamics simulations demonstrate that the AT splitting results from rapid Rabi oscillations induced by an ultrashort intense laser pulse in rovibrational coherent states that belong to different electronic terms. But Rabi oscillations will be damped because of the effects of rotation and alignment of the molecule in laser fields. The AT splitting in a photoelectron spectrum could be observed for a well-aligned molecule with sufficiently rapid Rabi oscillations. Only an adequately short laser pulse can induce AT splitting in a photoelectron spectrum. The effect of initial rotational temperature on the molecular dynamics is also studied.