Self-Referencing Spatiotemporal Characterization of Femtosecond Optical-Vortex Beams

Concurrently, a frequency-resolved optical gating (FROG) measurement using a type-II beta-barium borate (BBO) crystal is integrated to measure the temporal profile of the pulse at a selected sampling point with a high signal-to-noise ratio. Through a single scan of the interferometer arm, the tilted shearing-interference signal and the FROG trace are simultaneously recorded. From these measurements, the spectral phase over the pulse's spatial profile and the temporal envelope are subsequently retrieved, enabling the complete 3D reconstruction of the light field.

In our experiments, we successfully achieved self-referenced spatiotemporal reconstruction of ultrafast optical-vortex pulses with topological charges of |l| = 1, 2, and 3. The experimentally retrieved structures of these ultrafast optical-vortex beams exhibit striking agreement with theoretical simulations based on the Collins formula. This self-referencing technique provides a robust tool for characterizing spatially structured ultrafast pulses and holds significant potential for light-matter interaction studies.