Seminarium Optyczne

In addition to their oscillatory behavior, waves possess dynamical properties, such as energy, momentum, and angular momentum. The momentum of waves is associated with their propagation direction, i.e. the phase gradient. The circulation of the wave momentum density gives rise to orbital angular momentum (AM). Additionally, for waves described by vector fields, local rotation of the wavefield produces spin AM (or simply, spin). These dynamical wave properties become particularly significant in structured (i.e. inhomogeneous) wavefields. I will provide an introduction and overview of the momentum and AM properties for various classical waves: electromagnetic, sound, and water-surface waves. A unified field-theory approach, based on Noether’s theorem, offers a general framework to describe these diverse physical systems, encompassing longitudinal, transverse, and mixed waves with different dispersion characteristics. I will also discuss observable manifestations of the wave momentum and AM in terms of radiation forces and torques on small particles, which provide clear physical interpretations of the derived quantities.