An Alignment Microscope for Imaging Rotational Wavepacket Dynamics

We introduce a new method for encoding polarization-angle-dependent molecular alignment signals directly into the transverse spatial profile of a femtosecond laser beam. The approach employs a pump-probe setup in a common-path geometry. A radial–azimuthal polarization converter placed in the probe beam produces a doughnut-shaped beam whose local polarization varies continuously with azimuthal angle, thereby encoding the full range of linear polarization orientations from 0 to 2π within a single transverse beam profile. Consequently, the angular dependence of the molecular response can be recorded simultaneously rather than reconstructed through sequential measurements at different polarization angles. By varying only the pump–probe delay, this spatial encoding enables single-shot acquisition of the complete angular response at each delay and real-time visualization of the evolving molecular alignment pattern as the delay stage is scanned. This technique has enabled the experimental realization of an alignment microscope.