Decomposition of optical force into gradient and scattering parts*

Based on either mathematics or physics, it is natural to split the optical forces acting on small particles into the conservative gradient force and the nonconservative scattering force. While the former can trap small particles at a potential energy minimum, the latter can push or even pull small particles, thus transporting them.
Nevertheless, although its importance in understanding optical micromanipulation is recognized, these forces are only calculated for particles small or large compare to the light wavelength. Their true profiles for Mie sized particles, which are the most commonly encountered particles in real experiment, were not available. The difficulty lies in the complicated mathematics.
Here, we report several algorithms we developed to calculate the decomposed force for spherical particle with arbitrary size and composition and present some interesting results calculated by these algorithms [1-4].
[1] J. Du et. al., Sci. Rep. 7, 18042, (2017).
[2] Y. Jiang et. al., arXiv:1604.05138.
[3] H. Zheng et. al., Comput. Phys. Commun. 237, 188 (2019).
[4] Y. Jiang et. al., accepted by ACS Photonics, 10.1021/acsphotonics.9b00746