Power-tunable rotational dynamics of asymmetric vortex dipoles for material characterization

This study investigates the orbital angular momentum (OAM) and propagation dynamics of asymmetric vortex dipoles. The asymmetric spatial distribution of vortices carrying opposite topological charges yields a net OAM, inducing rotational motion during both linear and nonlinear propagation. Under linear conditions, the angular velocity of rotation correlates directly with the degree of asymmetry; vortex cores positioned farther from the dipole center exhibit greater angular velocities than those nearer the center. Diffraction limits the net rotation angle to less than 90 degrees in linear propagation. In contrast, during nonlinear propagation, the rotational dynamics depend not only on the asymmetry but also critically on the optical power. Modulating the input power enables precise control over the rotation trajectory, angle, and angular velocity, presenting a viable approach for optical field manipulation. Furthermore, this work proposes a method to experimentally quantify the nonlocal response of nonlinear materials by measuring the rotation angle of asymmetric vortex dipoles.