We examine the size dependence of gradient and nongradient contributions to the optically induced force on single, isolated nanometer-sized silver particles in water under plane-wave illumination. Using a recently developed method based on discrete-dipole approximation (DDA), we find that all contributions scale linearly with volume in this regime. This dependence can be rationalized by using semiempirical considerations based on the Mie–Debye theory. We also comment on a common approach to determining conservative and nonconservative force contributions on a single particle in an externally applied field. Our analysis suggests that the Mie–Debye theory cross sections cannot be used to evaluate conservative and nonconservative contributions to the force. Finally, we comment on aspects of the relationship between DDA and continuum-based treatments of optical force phenomena and find that inclusion of multiple scattering effects are essential to an understanding of the size dependence of the forces on mesoscopic particles.
© 2006 Optical Society of America
Optics at Surfaces
Original Manuscript: August 10, 2006
Manuscript Accepted: August 23, 2006
Vance Wong and Mark A. Ratner, "Size dependence of gradient and nongradient optical forces in silver nanoparticles," J. Opt. Soc. Am. B 24, 106-112 (2007)