Temporal analysis of fractional revivals of molecular observables following impulsive alignment
Résumé
Laser-induced impulsive alignment of symmetric linear molecules leads to time-dependent observables which are analyzed in terms of their spectral components. Signals appear as sums over positive integers ℓ of periodic components A2ℓ(t) with periods τ2ℓ=(2ℓcB0)−1, where B0 is the rotational constant in wave number units. Within each period τ2ℓ, four fractional revivals at times nτ2ℓ/4 (n=0,1,2,3) exhibit constant successive phase shifts (−1)ℓ+pπ/2 depending on the even-odd parity (p=0,1) of the initial rotational states. This analysis gives a comprehensive account of the so-called high-order revivals usually discussed in terms of fractional revivals within the period τ2 of the average value ⟨cos2ϑ⟩(t) of cos2(ϑ), where ϑ is the angle between the molecular axis and the alignment direction. These considerations are illustrated by experiments and numerical calculations of laser-induced impulsive alignment and tunnel ionization of CO2 molecules for which calculated ionization yields of fixed-in-space molecules are available.