Fig. 1. (a) A vortex beam illuminates on the surface of a rotating object vertically; (b) Pointing vector distribution of vortex beam

Fig. 2. (a) A vortex beam illuminates on the surface of a rotating object at general incidence; (b) Coordinate systems of the vortex beam and beam spot on the object surface

Fig. 3. Simulated distribution of rotational Doppler frequency shift at general incidence of vortex beam

Fig. 4. (a) Experiment setup of RDE; (b) Digital hologram of superimposed LG vortex; (c) Simulated intensity pattern; (d) Experimental intensity pattern; (e) Experimental intensity pattern of reflected beam

Fig. 5. Experimental frequency spectrum of RDE at coaxial incidence of vortex beam

Fig. 6. Experimental frequency spectrum of RDE at general incidence of vortex beam