Rotation of the spectral anomaly ("spectral eyes") of a propagating femtosecond polychromatic Bessel-Gauss beam around the phase singularity. Spectral maps were obtained by scanning the planes with a fiber delivering the signal to the grating spectrometer. The movie shows a complete rotation of the first spectral moment (centers of gravity) by 360° in axial steps of 10 µm (FOV: 162 µm x 181 µm, in close proximity to the singularity). The rotation continues over several cycles of rotation at a nearly constant rate and slows down in the region of spectral phase compensation
