Optical second-order skyrmionic hopfion

Due to their topological stability and spatial confinement, particle-like field configurations have gained significant interest in many areas of physics. Only recently, the first skyrmionic hopfion was proposed in light, but its higher-order analog in optics has stayed a theoretical construct so far, and direct experimental observations also prove difficult in non-optical systems. Here we overcome this challenge by the experimental realization and analysis of a second-order skyrmionic hopfion in the polarization and phase texture of a paraxial light field in three-dimensional space. Thereby, we exemplify advanced control of observed parameters in a localized space, pioneering further experimental studies on higher-order hopfions in optics and beyond.