Universal relationships between optical force/torque and orbital versus spin momentum/angular momentum of light (1511.08546v3)

Abstract: We establish universal relationships between optical force/torque on a general particle and different parts of linear and angular momentum (AM) of generic monochromatic optical field. It is rigorously proved that the optical force comes about by the transfer of orbital (canonical) optical momentum from light to matter, while the other part of optical momentum, known as spin momentum, does not generate optical force on matter but, instead, stays conserved even when the translational invariance is broken by putting particles into the optical fields. On the other hand, based on a generic multipole theory of optical torque, we demonstrate that the optical torque stems from the transfer of the total optical AM, including both orbital and spin AM, clarifying in generic case the long-standing confusion about whether the orbital AM can induce a spinning torque on a general particle in generic optical fields.