Fig. 2: Temporal evolution of the alignment of indole for the parallel alignment geometry (α = 0°).

a The solid lines show the measured 2D degree of alignment \({ < {\cos }^{2}\,{\theta }_{{{\mbox{2D}}}} > }_{{{{{X}}}}^{+}}^{\exp }\) for different fragments X⁺ and the dashed lines indicate values of the 2D degree of alignment obtained without alignment laser. Statistical error bars, representing the standard error, are shown for selected delays. The grey area shows the intensity profile of the alignment laser pulse. Also shown are the three expectation values \( < {\cos }^{2}{\theta }_{X{x}_{I}} > \), \( < {\cos }^{2}{\theta }_{Y{y}_{I}} > \) and \( < {\cos }^{2}{\theta }_{Z{z}_{I}} > \), with θ_Ij being the angles formed between the three main polarizability axes j ∈ (x_I, y_I, z_I) of indole and the three lab-frame axes I ∈ (X, Y, Z), and their computed values for the actual 3D alignment of indole. b The alignment revival structure of H⁺ fragments for longer times is shown in red, with the line thickness corresponding to the experimental standard error of the measurements. The dotted green line shows the fitted simulation for the H⁺ fragment. c Simulated 3D degree of alignment, characterized through the single-scalar metric \( < {\cos }^{2}\delta > \), see text/SI for details. Note the peak after truncation reaching \( < {\cos }^{2}\delta > =0.89\) at t = 3.3 ps.