The kinetic subsystem of light and its role in optical manipulation

Abstract

Optical manipulation has allowed for an increase in understanding across scientific fields including biology, chemistry, and atomic physics. Unfortunately, there is still significant debate as to how the dynamics of opticalmatter systems should be modeled. The reason for this is the myriad of formulations for the electromagnetic momentum and force density. While significant advances have been made in recent years to interpret the different formulations of electrodynamics, there remains some confusion. Most formulations include contributions from both matter and field. They may be interpreted as providing the canonical, total, or wave momentum, stress, and force. Examples include the well-known Gordon and Minkowski momenta. Conversely, it is widely accepted that the Abraham momentum of light corresponds to the kinetic subsystem. Changes in the kinetic momentum thus should provide center of mass-energy translations of matter providing a route to deriving equations of motion in optical manipulation experiments. In this paper, the idea of a kinetic formulation of electrodynamics is discussed. Consideration will be given to the three viewpoints which are most commonly argued. First, the kinetic subsystem should be postulated as a fundamental tenant of electrodynamics. Second, the kinetic subsystem of electrodynamics should not be postulated, but rather deduced by experimental and theoretical considerations. Third, a kinetic subsystem of electrodynamics cannot be uniquely defined in matter because the fields inside matter cannot be uniquely measured. Finally, it will be argued that identification of the kinetic subsystem of a particular optical manipulation experiment is not necessary nor preferred in most cases.