Experimental demonstration of dynamic spatiotemporal structured beams that simultaneously exhibit two orbital angular momenta by combining multiple frequency lines, each carrying multiple Laguerre-Gaussian modes

In general, there are different, relatively independent forms of orbital angular momenta at a given propagation distance, which might exhibit different dynamic spatial characteristics. One type involves a beam with a helical phase-front that rotates around its own beam center, such as a Laguerre-Gaussian (LG) beam with an azimuthal index not equal to zero. The other one is a Gaussian-like beam dot that revolves around a central axis. Here, we experimentally demonstrate the generation of a dynamic spatiotemporal (ST) structured beam that simultaneously exhibits both rotation and revolution at a given propagation distance. Nine Kerr frequency comb lines are coherently combined, each carrying a designed superposition of multiple LG modes containing one unique l value and multiple p values. Experimental results showthat the mode purity of the reconstructed revolving and rotating LG(30) beam is similar to 89% when both the beam waist and revolving radius (R) are 0.4 mm. Moreover, we explore the effects of the number of frequency comb lines and the R value on the mode purity of the generated ST beam. Consequently, we find that a higher mode purity can be achieved by involving more frequency comb lines or reducing the R. (C) 2022 Optica Publishing Group