Dielectric spheres as scatterers and/or antennas with anomalous radiation properties: Scattering and optical forces

The optical force on a small particle, immersed in an arbitrary nondissipative medium, with both electric and magnetic response to an impinging electromagnetic wave, is composed of three parts: two due to the induced electric and magnetic dipoles separately, ad one due to the interference between both. This leads to expressions for the gradient force, radiation pressure and curl components. In particular, for the magnetic force I tentatively introduce the concept of curl of the spin angular momentum density of the magnetic field. The force due to the interference between both dipoles is relevant in connection with the asymmetry of the angular distribution of scattered intensity emitted by the particle. At specific wavelengths, this distribution may be zero in the backward direction and almost zero in the forward direction. The result is that radiation pressure forces are a factor of 3 higher in the zero forward condition.