Diffractive imaging of a rotational wavepacket in nonlinear molecules

Abstract Imaging laser-induced rotational dynamics is an important and active field due to its applications in capturing reactions in the molecular frame and in molecular imaging. Ultrafast electron diffraction has been a powerful tool to study the dynamics of rotational wavepackets, however, studies have been limited to linear molecules due to the challenges in retrieving the probability density from the diffraction signal for nonlinear molecules. Here we show that we can directly retrieve the time-dependent rotational probability density of symmetric top molecules that were impulsively aligned by a femtosecond laser pulse. The evolving molecular alignment is probed using ultrafast electron diffraction, and the rotational wavepacket is extracted from the angle-resolved pair distribution functions. The experimental results are in good agreement with numerical simulations of the Schrodinger equation using the experimental conditions.