The spin and orbital angular momentum carried by electromagnetic pulses open new perspectives to control nonlinear processes in light–matter interactions, with a wealth of potential applications. In this work, we use time-dependent density functional theory (TDDFT) to study the nonlinear optical response of a free-electron plasmonic nanowire to an intense, circularly polarized electromagnetic pulse. In contrast to the well-studied case of the linear polarization, we find that the nth harmonic optical response to circularly polarized light is determined by the multipole moment of order n of the induced nonlinear charge density that rotates around the nanowire axis at the fundamental frequency. As a consequence, the frequency conversion in the far field is suppressed, whereas electric near fields at all harmonic frequencies are induced in the proximity of the nanowire surface. These near fields are circularly polarized with handedness opposite to that of the incident pulse, thus producing an inversion of the spin angular momentum. An analytical approach based on general symmetry constraints nicely explains our numerical findings and allows for generalization of the TDDFT results. This work thus offers new insights into nonlinear optical processes in nanoscale plasmonic nanostructures that allow for the manipulation of the angular momentum of light at harmonic frequencies.

It is well known that a magnetic monopole-electric charge system carries an angular momentum in its electromagnetic fields. Here we show that in the Dirac string formulation of magnetic charge the monopole-electric charge system also carries a momentum in its electromagnetic fields. This overlooked field momentum arises from the Coulomb electric field of the electric charge and the solenoidal magnetic field of the Dirac string. This implies that the monopole-charge system must either: (i) carry a ``hidden momentum"in the string, indicating that the string is real, or (ii) that the monopole-charge system violates the center-of-energy theorem. The overall conclusion is that the Dirac monopole with a {\it regulated} Dirac string is not a true monopole, and is not even a good effective description for topological monopoles ({\it e.g.} the 't Hooft-Polyakov monopole outside the core).

Radiative Reactions and Coherence Modeling in the High Altitude Electromagnetic Pulse A high altitude nuclear electromagnetic pulse (EMP) with a peak field intensity of 5 x 10^4 V/m carries momentum that results in a retarding force on the average Compton electron (radiating coherently to produce the waveform) with magnitude near that of the geomagnetic force responsible for the coherent radiation. The retarding force results from a self field effect. The Compton electron interaction with the self generated magnetic field due to the other electrons accounts for the momentum density in the propagating wave; interaction with the self generated electric field accounts for the energy flux density in the propagating wave. Coherent addition of radiation is also quantitatively modeled. Published as: Phys.Rev.A37:1969-1977,1988 DOI: 10.1103/PhysRevA.37.1969 arXiv categories: physics.gen-ph physics.class-ph

We find exact, simple solutions to the Proca version of Maxwell's equations with magnetic sources. Several properties of these solutions differ from the usual case of magnetic charge with a massless photon: (i) the string singularities of the usual 3-vector potentials become real singularities in the magnetic fields; (ii) the different 3-vector potentials become gauge inequivalent and physically distinct solutions; (iii) the magnetic field depends on $r$ and $\theta$ and thus is no longer rotationally symmetric; (iv) a combined system of electric and magnetic charge carries a field angular momentum even when the electric and magnetic charges are located at the same place i.e. for dyons); (v) for these dyons one recovers the standard Dirac condition despite the photon being massive. We discuss the reason for this. We conclude by proposing that the string singularity in the magnetic field of an {\it isolated} magnetic charge suggests a confinement mechanism for magnetic charge, similar to the flux tube confinement of quarks in QCD.

Structured light beams with engineered topological properties offer a powerful means to control spin angular momentum (SAM) and optical chirality, key quantities shaped by spin-orbit interaction (SOI) in light. Such effects are commonly associated with non-paraxial focusing or light-matter interfaces. Here, we demonstrate that higher-order Poincaré modes carrying a tunable Pancharatnam topological charge ℓ_p enable deterministic control of SOI entirely in free space and within the paraxial regime. We show that modulation of ℓ_p drives a measurable radial separation of circular polarization components - a free-space optical Hall effect arising from propagation-induced mechanisms alone. The effect originates from differential Gouy-phase evolution and radial divergence between the two circular components of an initially spin-balanced vector beam. This identifies ℓ_p as a single, tunable parameter linking Pancharatnam topology to paraxial spin-orbit coupling, establishing a simple and material-independent route to generate and control optical chirality and SAM. This approach provides new opportunities for tunable optical manipulation, chiral sensing, and high-dimensional photonic information processing.