Abstract

Radiation force induced by a laser beam has been widely utilized to trap or to manipulate the particles of micrometer and nanometer scale over the past 30 years. Various experimental instruments, e.g. optical tweezers and optical stretcher, have been developed to meet the requirements of non-intrusive detection and control of the micro-objects, e.g. droplets, cells, and DNA strands. Regarding the theoretical aspect, the Lorenz-Mie theory has been extended to deal with the case of non-plane wave illumination and the force exerted on a sphere by a focused laser beam has been analytically predicted. Such a theory, referred as generalized Lorenz-Mie theory (GLMT) has the potential to be further extended to some regularly shaped particles when the incident beam is expanded in the coordinates mirroring the geometry of these particles, as exemplified by our previous work on scattering, net force and torque prediction for a spheroid. Recently, our progress on predicting the stress profile on the surface of a spheroid has been made. The results predicted by GLMT are verified by geometrical optics which has a more straightforward physical interpretation of the mechanical effect of light. On the basis of GLMT , influences of particle’s non-sphericity and layer-structure, as well as incident beam shape on the stress profile can be known.